Main components of a computerMultimedia devicesOther peripheral .pdf

Main components of a computer
Multimedia devices
Other peripheral devices
1) computer
2) monitor
3) hard disk/ hard drive
4) keyboard
5) mouse / trackball /
touch pad
1) CD-ROM / DVD drive
2) video card
3) soundcard
4) speakers
5) headphones / headset
6) microphone
1) printer
2) scanner
3) CD- burner (CD- recorder,
CD-R/CD-RW drive)
4) modem
5) USB flash drive
6) webcam
7) digital camera
8) digital voice recorder
9) camcorder
Floppy disk working mechanism
Floppy disks work in a similar manner to cassette tapes and the magnetic strip on a credit card.
The floppy disk is constructed of stur plastic that is embedded with a thin iron oxide coating on
both sides. The head of the floppy disk drive easily manipulates the magnetic coating on the disk
to store information. Information is recorded on circular tracks and triangular sections. A special
head in the drive erases the area to be written before recording occurs. This head is wider than
the head used for recording and reading information to ensure recorded information is not
contaminated from previous information recorded nearby.

When reading the disk, the head moves to the appropriate track and sector quickly without
touching the disk. This is an improvement over older cassette tape storage that required a rewind
or fast forward movement to retrieve information. Floppy disks contain a safety slide on the side
of the case. If the slide is moved to create an opening, the drive will not record on the disk.
Introduction
A peripheral is a piece of computer hardware that is added to a computer in order to expand its
abilities. The term peripheral is used to describe those devices that are optional in nature, as
opposed to hardware that is either demanded or always required in principle. There are all
different kinds of peripherals you can add your computer. The main disctinction among
peripherals is the way they are connected to your computer. They can be connected internally or
externally.
Buses
A bus is a subsystem that transfers data between computer components inside a computer or
between computers. Unlike a point-to-point connection, a bus can logically connect several
peripherals over the same set of wires. Each bus defines its set of connectors to physically plug
devices, cards or cables together. There are two types of buses: internal and external. Internal
buses are connections to various internal components. External buses are connections to various
external components. There are different kinds of slots that internal and external devices can
connect to.
Internal
Types of Slots
There are many different kinds of internal buses, but only a handful of popular ones. Different
computers come with different kinds and number of slots. It is important to know what kind and
number of slots you have on your computer before you go out and by a card that matches up to a
slot you don’t have.
PCI
PCI (Peripheral Component Interconnect) is common in modern PCs. This kind of bus is being
succeeded by PCI Express. Typical PCI cards used in PCs include: network cards, sound cards,
modems, extra ports such as USB or serial, TV tuner cards and disk controllers. Video cards
have outgrown the capabilities of PCI because of their higher bandwidth requirements.
PCI Express
PCI Express was introduced by Intel in 2004. It was designed to replace the general-purpose PCI
expansion bus and the AGP graphics card interface. PCI express is not a bus but instead a point-
to-point conection of serial links called lanes. PCI Express cards have faster bandwidth then PCI
cards which make them more ideal for high-end video cards.
PCMCIA

PCMCIA (also referred to as PC Card) is the type of bus used for laptop computers. The name
PCMCIA comes from the group who developed the standard: Personal Computer Memory Card
International Association. PCMCIA was originally designed for computer memory expansion,
but the existence of a usable general standard for notbeook peripherals led to many kinds of
devices being made available in this form. Typical devices include network cards, modems, and
hard disks.
AGP
AGP (Accelerated Graphics Port) is a high-speed point-to-point channel for attaching a graphics
card to a computer’s motherboard, primarily to assist in the acceleration of 3D computer
graphics. AGP has been replaced over the past couple years by PCI Express. AGP cards and
motherboards are still available to buy, but they are becoming less common.
Types Of Cards
Video Card
A video card (also known as graphics card) is an expansion card whose function is to generate
and output images to a display. Some video cards offer added functions, such as video capture,
TV tuner adapter, ability to connect multiple monitors, and others. Most video cards all share
similar components. They include a graphics processing unit (GPU) which is a dedicated
microprocessor optimized for 3D graphics rendering. It also includes a video BIOS that contains
the basic program that governs the video card’s operations and provides the instructions that
allow the computer and software to interface with the card. If the video card is integrated in the
motherboard, it may use the computer RAM memory. If it is not it will have its own video
memory called Video RAM. This kind of memory can range from 128MB to 2GB. A video card
also has a RAMDAC (Random Access Memory Digital-to-Analog Converter) which takes
responsibility for turning the digital signals produced by the computer processor into an analog
signal which can be understood by the computer display. Lastly, they all have outputs such as an
HD-15 connector (standard monitor cable), DVI connector, S-Video, composite video or
component video.
Sound Card
A sound card is an expansion card that facilitates the input and output of audio signals to/from a
computer under control of computer programs. Typical uses for sound cards include providing
the audio component for multimedia applications such as music composition, editing video or
audio, presentation/education, and entertainment. Many computers have sound capabilities built
in,, while others require additional expansion cards to provide for audio capability.
Network Card
A network card is an expansion card that allows computers to communicate over a computer
network. It allows users to connect to each other either by using cables or wirelessly. Although

other network technologies exist, Ethernet has achieved near-ubiquity for a while now. Every
Ethernet network card has a unique 48-bit serial number called a MAC address, which is stored
in ROM carried on the card. You can learn more about networking in the introduction to
networking lesson.
external
Types of Connections
USB
USB (Universal Serial Bus) is a serial bus standard to interface devices. USB was designed to
allow many peripherals to be connected using a single standardized interface socket and to
improve the plug-and-play capabilities by allowing devices to be connected and disconnected
without rebooting the computer. Other convient features include providing power to low-
consumption devices without the need for an external power supply and allowing many devices
to be used without requiring manufacturer specific, individual device drivers to be installed. USB
is by far the dominating bus for connecting external devices to your computer.
Firewire
Firewire (technically known as IEEE 1394 and also known as i.LINK for Sony) is a serial bus
interface standard for high-speed communications and isochronous real-time data transfer,
frequently used in a personal computer. Firewire has replaced Parallel ports in many
applications. It has been adopted as the High Definition Audio-Video Network Alliance (HANA)
standard connection interface for A/V (audio/visual) component communication and control.
Almost all modern digital camcorders have included this connection.
PS/2
The PS/2 connector is used for connecting some keyboards and mice to a PC compatible
computer system. The keyboard and mouse interfaces are electrically similar with the main
difference being that open collector outputs are required on both ends of the keyboard interface
to allow bidirectional communication. If a PS/2 mouse is connected to a PS/2 keyboard port, the
mouse may not be recognized by the computer depending on configuration.
Devices
Removable Storage
The same kinds of CD and DVD drives that could come built-in on your computer can also be
attached externally. You might only have a CD-ROM drive built-in to your computer but you
need a CD writer to burn CDs. You can buy an external CD writer that connects to your USB
port and acts the same way as if it was built-in to your computer. The same is true for DVD
writers, Blu-ray drives, and floppy drives. Flash drives have become very popular forms of
removable storage especially as the price of flash drives decreases and the possible size for them
increases. Flash drives are usually USB ones either in the form USB sticks or very small,

portable devices. USB flash drives are small, fast, removable, rewritable, and long-lasting.
Storage capacities range from 64MB to 32GB or more. A flash drive does not have any
mechanically driven parts so as opposed to a hard drive which makes it more durable and smaller
usually.
Non-removable Storage
Non-removable storage can be a hard drive that is connected externally. External hard drives
have become very popular for backups, shared drives among many computers, and simply
expaning the amount of hard drive space you have from your internal hard drive. External hard
drives come in many shapes and sizes like flash drives do. An external hard drive is usually
connected by USB but you can also have a networked hardrive which will connect to your
network which allows all computers on that network to access that hard drive.
Input
Input devices are absolutely crucial to computers. The most common input devices are mice and
keyboards which barely every computer has. A new popular pointing device that may eventually
replace the mouse is touch screen which you can get on some tablet notebooks. Other popular
input devices include microphones, webcams, and fingerprint readers which can also be built in
to modern laptops and desktops. A scanner is another popular input device that might be built-in
to your printer.
Output
There are lots of different kinds of output devices that you can get for your computer. The
absolute most common external output device is a monitor. Other very popular output devices
are printers and speakers. There are lots of different kinds of printers and different sizes of
speakers for your computer. Monitors are connected usually through the HD-15 connector on
your video card. Printers are usually connected through a USB port. Speakers have their own
audio out port built-in to the sound card.
Types of Storage Devices
Physical components or materials on which data is stored are called storage media.Hardware
components that read/write to storage media are called storage devices.
Two main categories of storage technology used today are magnetic storage and optical storage.
Primary magnetic storage
o Diskettes
o Hard disks (both fixed and removable)
o High capacity floppy disks
o Disk cartridges
o Magnetic tape
Primary optical storage

o Compact Disk Read Only Memory (CD ROM)
o Digital Video Disk Read Only Memory (DVD ROM)
o CD Recordable (CD R)
o CD Rewritable (CD RW)
o Photo CD
Magnetic Storage Devices
Purpose of storage devices à to hold data even when the computer is turned off sothe data can be
used whenever needed. Storage involves writing data to the medium and reading from the
medium. Writing data à recording the data on the surface of the disk where it is stored for later
use. Reading data à retrieving data from thesurface and transferring it into the computers
memory for use.
Diskette drives, hard drives and tape drive all use the same type of medium à use similar
techniques for reading/writing data. Surfaces of diskettes and magnetic tape
are all coated with a magnetically sensitive material such as iron oxide.
The principle use to store data is that of polarisation – all the ions in the magnetic
material align themselves in one direction. Just as a transistor can represent binary
“on” or “off”, the orientation of the magnetic field can be used to represent data. A
magnet has one important advantage over a transistor à it can maintain it’s state
without a continual supply of electricity.
Surfaces of disks are coated with millions of tiny iron particles so data can be stored
on them. Each particle acts as a magnet, taking on a magnetic field when subjected to
an electromagnet. The read/write heads of a disk drive contain electromagnets, which
generate magnetic fields in the iron on the storage medium as the head passes over the
disk. The read/write heads store a string of 1s and 0s by alternating the direction of
the current in the electromagnet.
To read data the process is reversed. The read/write heads pass over the disk while no
current is flowing through the electromagnet. The storage medium has a charge and
the electromagnet does not à storage medium changes the magnet in the head which
causes a small current to flow through the head in one direction or the other
depending on the polarity of the field. The disk drive senses direction of flow and
data is sent from the head into memory.
Magnetic Disks
Diskette drives and hard disk drives are the most commonly used storage devices in
PCs. Both fall into the magnetic storage category because they record data as
magnetic fields.
Fundamental differences and similarities between the two:

· A diskette contains a single flat piece of plastic (the disk) coated with iron
oxide enclosed in vinyl or plastic cover. A hard disk contains one or more
rigid metal platters coated with iron oxide permanently enclosed in a hard disk
drive.
· Diskettes are small and portable (they can be removed from diskette drives).
Hard disks are usually built into the computer and are not portable (unless the
computer is). Exceptions are removable hard disks and external hard drives
which can be detached from the system.
· Floppy disks store only 1.44 MB although special floppy disks offer higher
capacity. New hard disks can store several thousand times as much data as a
diskette.
· Hard drives are much faster than diskettes, their disks spin faster and they
locate data on the disks surface in much less time.
Almost all PCs sold today come with a hard disk and one disk drive. Some computers
also feature a third built in magnetic device – a device that uses high capacity floppy
disks.
How data is organised on a magnetic disk
Before the computer can use a diskette to store data, the disks surface must be
magnetically mapped so that the computer can go directly to a specific point without
searching through all the data. This process of mapping a disk is called formatting or
initialising. When you purchase a new disk, they should be formatted for either PC or
Mac.
It may be helpful to reformat disks from time to time as this deletes all the data on
disk. During the formatting you process you can also determine whether the disk has
any faulty spots and you can copy important system files onto the disk.
Hard disks must also be formatted so that the computer can locate data on them.
When you buy a computer, the hard disk has already been formatted correctly and
probably contains some programs and data. You can format your hard disk if
necessary but the process is different to that for a diskette.
Modern diskettes store data on both sides of the disk (numbered side 0 and side 1) and
each side has its own read/write head. When formatting a disk, the disk creates a set
of magnetic concentric circles called tracks, on each side of the disk. The number of
tracks required depends on the type of disk. Most high -density diskettes have 80
tracks on each side. A hard disk may have several hundred tracks on each side of
each platter. Each track is a separate circle. These are numbered from the outermost
circle to the innermost, starting with zero.

Each track on a disk is also split into smaller parts. Imagine slicing a disk as you
would a pie. Each slice cuts across all the tracks resulting in short segments or
sectors. A sector can contain up to 512 bytes. All the sectors are numbered in one
long sequence so the computer can access each small area on the disk with a unique
number. This scheme simplifies a 2 dimensional set of co-ordinates into a single
numeric address.
If the diskette has 80 tracks on each side and each track contains 18 sectors à 1440
sectors per side à 2880 sectors per disk. This configuration is true regardless of the
length of the track. The diskettes outermost track is longer than the innermost one but
each track is still divided into the same number of sectors. Regardless of physical size
all the sectors hold the same number of bytes i.e. the shortest, innermost sectors hold
the same amount of data as the longest outermost ones.
A disks allocation of sectors per track is somewhat wasteful because the outer longer
tracks could theoretically hold more data than the shorter inner ones. For this reason
hard disks allocate more sectors to the longer tracks on the disks surface. As you
move towards the disks centre, each subsequent track has fewer sectors. This
arrangement takes advantage of the hard disks potential capacity and enables a typical
hard disk to store data more efficiently than a floppy disk. Because many hard disks
allocate sectors in this manner, their sectors per track specification are often given as
an average. Such hard disks are described as having an average of x sectors per track.
Because files are not usually a size that is an even multiple of 512 bytes, some sectors
contain unused space after the end of the file. In addition the Windows OS allocates a
group of sectors called a cluster to each file stored on a disk. Cluster sizes vary on
the size and type of disk, but can range from 4 à 64 sectors. A small file that
contains only 50 bytes will only use a portion of the first sector of a cluster leaving
the remainder of the sector and cluster allocated but unused.
The different capacities of disks are generally a function of the number of sides,
tracks and sectors per track. Floppy disks have only a few standard types and formats
but hard disks come in a variety of sizes so their capacities vary greatly.
A sector is the smallest unit with which any disk drive can work. Each bit and byte
within a sector can have different values but the drive can read or write only whole
sectors at a time. If the computer needs to change just 1 byte out of 512 it must
rewrite the whole sector.
How the OS finds data on a disk
A computer's Operating system can locate data on a disk because each track and
sector is labelled, and the location of all data is kept in a special log on the disk. The

labelling of tracks and sectors is called performing a logical format (also called low
level format or soft format). A commonly used logical format by windows creates 4
disk areas
1. Master boot record (MBR)
2. File – allocation table (FAT)
3. Root folder or directory
4. Data Area
Master boot record is a program that runs when you first start the computer. It
determines whether the disk has the basic components necessary to run the operating
system correctly. If the program determines that the correct files are present and disk
has a valid format, it transfers control to one of the OS programs that continues the
system start up (known as booting). Boot record also describes characteristics such
as number of bytes per sector and number of sectors per track.
FAT is a log that records the location of each file and the status of each sector. When
you write to a disk, the OS checks the FAT for an open area, stores the data and then
identifies the file and its location in the FAT. The FAT solves a common filing
problem, what happens when you load a file; increase its size by adding to it and then
save it again? The OS checks the FAT for free areas and places pointers that in it that
links together the nonadjacent parts of the file. In other words it splits the file by
allocating new space for the overflow, the pointers in FAT enable the OS to put the
file back together again.
When a file is saved in this way it becomes fragmented. Fragmented files cause side
effects such as taking longer to save and load.
Users do not see the information in FAT but often use the information. A folder (also
called a directory) is a tool for organising files on a disk. Folders can contain files or
other files so it is possible to set up hierarchical systems of folders on your computer.
The top folder on any disk is called the root folder (or root directory). When you
use the OS to view the contents of a folder, the OS lists specific information about
each file in the folder such as name, size, date of creation or last modification and so
on.
The part of the disk that remains free after the boot sector, FAT and root folder have
been created is called the data area, because that is where the data is stored!
Diskettes (Floppy Disks)
The diskette drive includes a motor that rotates the disk on a spindle and the
read/write heads that can move to any spot on the surface of the disk as it spins. This
allows the heads to access data randomly rather than sequentially – the heads can skip

from one spot to another without having to scan through all the data in between.
Diskettes spin at approx. 300 revolutions per minute. The longest it can take to
position a point on the diskettes under the read/write heads is the amount of time for
one revolution – 0.2 second. The farthest the heads have to move is from the centre
of the diskette to the outside edge (or vice versa). The heads can do this in less time –
about 0.17 seconds.
Because both operations occur at the same time (spinning the disk and moving the
heads over the surface), the maximum time to position the heads over a given location
on the diskette – known as maximum access time – remains the greater of the two
times, 0.2 second.
The maximum access time for diskettes can be even longer, however, because they do
not spin when they are not being used. It can take about 0.5 second to rotate the disk
from a dead stop.
Most common uses for disks
· Moving files between computers not connected by a network or
communication hardware – one of the easiest ways to move data from one
computer to another is to copy it onto diskette and use the diskette in another
computer.
· Loading new programs onto a system – Large programs are usually delivered
by CD-ROM but many programs are still sold on diskette. You install it by
copying the contents of the disks onto the hard drive and then running a small
program, which installs the files automatically.
· Backing up data or programs – Primary copy of data or programs are stored
on the hard drive, Backing up is the process of creating a duplicate copy for
safekeeping. To protect against data loss it is wise to back up a hard disk.
Due to the limited storage capacity diskettes are used to back up small data
files rather than programs or entire hard disks.
Types of Diskettes
1980’s à most PCs used 5.25-inch diskettes.
Now à almost completely replaced by the 3.5-inch.
The size refers to the diameter of the disk and is not an indication of capacity.
The 5.25 type is encased in a flexible vinyl envelope with an oval cutout that allows
read/write heads access to the disk. The 3.5 type is encased in a hard plastic shell
with a sliding shutter. On insertion into the drive the shutter slides back to expose the
surface to the read/write heads.
Diskette capacities

Both types have evolved from lower to higher densities. The density is a measure of
the capacity of the surface of the disk, the higher the density à the more closely the
iron oxide particles are packed à the more data a disk can store.
Early versions of disks were double density (DD). As diskette media improved à
storage capacity improved. DD diskettes have been replaced by high density (HD)
ones providing significantly more storage.
Diameter Sectors/ Bytes/ Total
(inches) Type Tracks track Sectors sector bytes
5.5 DD 40 9 720 512 360k
5.5 HD 80 15 2400 512 1200k
3.5 HD 80 9 1440 512 720k
3.5 HD 80 18 2880 512 1440k
3.5 HD 80 36 5760 512 2880k
Macs never used 5.25 diskettes.
DD Mac disk holds 800k not 720k.
The Extra density disk holds more data than a regular 1.44 MB disk but needs a
special hard drive.
Hard Disks
Hard disk is still the most common storage device for all computers. Like diskettes
hard drives store data in tracks divided into sectors. Physically however they look
quite different to diskettes.
Includes one or more metal platters mounted on a central spindle, like a stack of rigid
diskettes. Each platter is covered with a metal coating and the entire unit is contained
in a sealed chamber. The hard disk and drive are a single unit which includes the hard
disk, the motor that spins the platters and a set of read/write heads. Because you
cannot remove the disk from the drive the terms hard disk and hard drive are used
interchangeably.
Hard drives have become the primary storage devices for PCs because they are
convenient and cost effective. They outperform diskettes in both speed and capacity.
Hard disks offer capacities from several hundred MB and more. Most entry level PCs
now come with hard disks of at least 6.8MB.
Two important physical differences between hard disks and diskettes account for the
differences in performance.
1. Hard disks are sealed in a chamber
2. Hard disk consists of a rigid metal platter (usually aluminium) rather than
flexible Mylar.

Hard disk spin between 3600 rpm and 7200 rpm compared to a diskette 300 rpm. The
speed at which the disk spins is a major factor in overall performance. The rigidity of
the disk and the high-speed rotation allows more data to be recorded on the surface.
Waving a magnet past an electric coil causes a current to flow. The faster you wave
the magnet and the closer the magnet is to the coil, the larger the current generated in
the coil. The disk that spins faster can use smaller magnetic charge to make current
flow to the read/write head. The drives heads can also use a lower density current to
record data on the disk.
Not only do hard disks pack the data closer together they also hold more data because
they usually include multiple platters stacked one on top of each other. This
configuration means that the disk has more than 2 sides, in addition to side 0 and 1
there are sides 2, 3, 4, and so on. Larger capacity disks may use 12 platters but both
side of every platter are not always used.
The number of sides that the disk uses is specified by the number of read/write heads.
A particular disk may have 6 disks platters (12 sides) but only 11 heads à one side is
not used to store data. Unused side is often the bottom one.
The term cylinder is often used to refer to the same track across all the disks. Track 0
(outermost track) on every disk is cylinder 0.
Hard disk generally store 512 bytes of data in a sector, but can have more sectors per
track – 54, 63 or even more sectors per track are not uncommon.
Computation of a hard disks capacity is identical to that for other disks but the
numbers are larger. Breakdown of capacity for a 50 GB hard disk, assuming 11
platters, 264,528 tracks, 369 sectors per track:
12024 cylinders x 22 heads (sides)
= 264528 tracks
264528 tracks x 369 avg. sectors/track
= 97,610,823 sectors
97610823 sectors x 512 bytes
=49,976,754,984 bytes
(Approx)
If the actual numbers of sectors per track were taken into account instead of an
average, the calculation would be more difficult and the resulting number of bytes
would be higher.
In spite of capacity and speed advantages there is one major drawback à to achieve
optimum performance the read/write heads must be extremely close to the surface of
the disk without actually touching it. The read/write heads fly so close to the disk that

a human hair, a dust particle or even a fingerprint would bridge the gap and cause the
head to crash. A head crash – in which the head touches the disk – can destroy the
data stored in the area of the crash. A severe head crash can destroy the read/write
head.
Removable high capacity magnetic disks
· High capacity floppy disks
Disks with the same dimensions as 3.3-inch floppy diskette or slightly larger
have a much greater capacity than a standard diskette. Popular high capacity
floppy disks include
1. A HiFD - (high capacity floppy drive) made by Sony Electronics Inc.
Looks like a normal 3.5-inch disk but can store up to 20 MB. This
drive can read and format double density and high-density floppy disks
in addition to HiFD disks.
2. SuperDisk – made by Imation, same dimensions as standard 3.5-inch
but formatted to hold 120 MB. Drives are compatible with highdensity
3.5-inch diskettes.
3. Zip Disks – made by Iomega Corp. Available in 100 MB and 250 MB
capacities and require a special disk drive and utility software. Slightly
larger than normal and are not compatible with ordinary floppy.
· Hot-Swappable Hard Disks
At the high end of price and performance. Sometimes used on high-end
workstations or servers that require large amounts of storage. They allow the
user to remove (swap out) a hard disk and insert (swap in) another while the
computer is still on (hot). The removable disk contains the disk, drive and
read/write heads in a sealed box.
· Disk Cartridges
Most removable disks work like a diskette, a disk in a plastic case that is
inserted into or removed from the drive. The disk and case are called disk
cartridges. Do not offer the same storage as true hard disks, they hold more
data than diskettes and are faster and just as portable.
Tape Drives
Read and write data to the surface of a tape the same way as an audiocassette –
difference is that a computer tape drive writes digital data.
Best use of tape storage is for data that is not used often, such as backup copies of
your hard disk. Because a tape is a long strip of magnetic material, the tape drive has
to write the data to it serially – 1 byte after another. This is inherently slower than the

direct access provided by media such as disks. When you want to assess specific data
on a tape the drive has to scan through all he data that you don’t need to get to the
data that you want. Result à Slow access time. The access time varies depending on
the speed of the drive, length of tape and position on the tape to which the head wrote
the data in the first place.
Despite the long access time tape drives are well suited for certain purposes –
especially backing up a systems entire hard disk. Backing up using high capacity
disks or disk cartridges is usually expensive. Many people now use recordable CDs
to back up their system. This option is more expensive than tapes, and unless CDRW
are used the data cannot be overwritten. Capacities of tapes can be as high as 100
GB and more, tape offers an inexpensive way to store a lot of data on a single
cassette.
Special type of tape drive uses digital audiotape (DAT) to achieve high storage
capacities. DAT drives typically have multiple read and write heads built into a small
wheel or cylinder that spins near the tape at high speed. The tape moves past the
heads with a slower speed. The write heads on the spinning wheel each write the data
with opposite magnetic polarities on overlapping areas of the tape. Each read head
reads only one polarity or the other. The result is a high density per inch of tape.
Although DAT tapes are relatively inexpensive the drives can be expensive when
compared to standard tape drives.
Optical Storage Devices
The most popular alternative to magnetic storage systems are optical storage media.
The most widely used type of optical storage medium is the compact disk (CD),
which is used in CD-ROM, DVD-ROM, CDR, CDRW and PhotoCD systems.
Since the mid 1990s nearly all PCs have been sold with a built in CD-ROM drive.
Consumers are now buying more systems with DVD-ROM drives rather than
standard CD-ROM units. These devices fall into the optical storage category because
they store data on a reflective surface so that it can be read by a beam of laser light. A
laser uses concentrated, narrow beam of light, focused and directed with lenses,
prisms and mirrors. The tight focus of the laser beam is possible because all the light
is of the same wavelength.
CD-ROM
The familiar audio compact disk is a popular medium for storing music. In the
computer world, the medium is called compact disk read only memory (CD-ROM).
This uses the same technology used to produce music CDs.
The CD-ROM drive for music or data reads 0s and 1s from a spinning disk by

focusing a laser on the disks surface. Some areas of the disk reflect the laser light into
a sensor, other areas scatter the light. A spot that reflects the laser beam is interpreted
as a 1 and the absence of a reflection is interpreted as a 0.
Data is laid out on a CD-ROM disk in a long, continuous spiral that starts at the outer
edge and winds inwards towards the centre. Data is stored in the form of lands,
which are flat areas on the metals surface, and pits, which are depressions or hollows.
A land reflects the laser light into the sensor (a data bit of 1) and a pit scatters the light
(a data bit of 0).
On a full CD-ROM the spiral of data stretches almost 3 miles long. A standard CD
can store 650 MB of data or about 70 mins of audio.
CD-ROM Speeds
Compared to hard disk drives CD-ROM drives are quite slow, in part because the
laser reads pits and lands one bit at a time. Another reason is the rotational speed of
the disk. Like a track on a magnetic disk the track of an optical disk is split into
sectors. However the sectors are laid out quite differently than they are on magnetic
disks.
The sectors near the middle of the CD wrap farther around the disk than those near the
edge. For the drive to read each sector in the same amount of time it must spin the
disk faster when reading the sectors near the middle and slower when reading the
sectors near the edge. Changing the speed of rotation takes time – enough to seriously
impair the overall performance of the CD-ROM drive. The first CD-ROM drives read
data at 150 KBps and were known as single speed drives. This rate is much slower
than that of a typical hard drive which transfers data at rates of 5 – 15 MBps.
Presently CD-ROM drives read data 2 à 52 times faster than first models (300 à
7800 KBps).
Even with the changing speed of the disk reading data from an optical medium is a
relatively simple undertaking. Writing data however is another matter. The medium
is a foil disk that is physically pitted to reflect or scatter the laser beam. The disk is
then covered in a plastic coating and it is difficult to alter the surface of the disk after
it has been stamped.
CD-ROM Uses
The fact that you must use special technologies to write data to an optical disk does
not mean that this storage medium is not useful. In fact many applications rely on
huge volumes of data that rarely change. Because of the high precision and data
density possible with CD-ROM, a single CD typically can hold about 650 MB of data.
Software companies can distribute their products on CD-ROM. Because of the high

capacity and the fact that 1 CD much cheaper to produce than a set of diskettes, many
software publishers regard CDs as the distribution medium of choice.
DVD-ROM
Digital video (or versatile) disk read only memory, is a high-density medium capable
of storing a full-length movie on a single disk the size of a CD.
Achieves such high storage capacities by using both sides of the disk and special data
compression technologies. The latest generation of DVD-ROM use layers of data
tracks; the laser beam reads data from the first layer and then looks through it to read
data from the second layer.
Each side of a standard DVD-ROM can hold up to 4.7 GB. Dual layer DVD-ROM
can hold 17 GB of data.
CD-R, CD-RW, PhotoCD
CD-R allows you to create your own CD-ROM disks that can be read by any CDROM
drive. After the information has been written to the CD it cannot be changed.
Using CD-RW drives the user can write and overwrite data onto CDs. With a CDRW
data can be revised in the same manner as a floppy disk.
One popular form of recordable CD is PhotoCD, a standard developed by Kodak for
storing digitised photographic images on a CD. Many film-developing stores now
have PhotoCD drives that can store your photos and put them onto a CD.
Measuring Drive Performance
Average Access Time
For a storage device the average access time (or seek time ) is the amount of time the
device takes to position its read/write heads over any spot in the medium. This
measurement is an average because access times can vary greatly depending on the
distance between the heads original location and their destination.
For storage devices access times are measured in milliseconds (ms). For memory
devices access times are measured in nanoseconds (ns).
In a disk drive the access time depends on a combination of 2 factors.
1. Revolutions per minute (rpm).
2. Time taken to move the heads from one track to another.
Device Typical Access Time
Static RAM (SRAM) 5 – 15 ns
Dynamic RAM (DRAM) 50 – 70 ns
ROM 55 – 250 ns
Hard disk drives 6 – 12 ms
CD-ROM drives 80 – 800 ms

Tape Drives 10 – 500 s
File Compression
One solution to the storage problem is to compress data. File compression or data
compression is the technology for shrinking the size of a file, thereby freeing up
space for more data and programs to reside on the disk.
Entire hard disks, floppy disks, or individual files can be compressed as much as a 3:1
ratio. File compression is performed by software that uses mathematical algorithms
to squeeze the data into smaller chunks by removing information that is not vital to
the file or data. When the file is returned to its original size this data is reinserted so
that the original data is reproduced exactly as it was before compression.
A utility used to compress one or more files shrinks the selected files and stores them
inside a new file with its own name. The resulting file is called an archive file
because it stores the compressed data inside.
Data transfer rate
The speed at which a device can transfer data – how long it takes for one device to
transfer data to another device. Speeds are expressed as a rate, or as some amount of
data per unit time. When measuring a devices data transfer rate (throughput) the
time is measured in seconds, but units of data may be measured in bytes, KB, MB or
GB.
Speeds for hard disks are generally high, from around 15 MBps to 80 MBps and
higher. CD-ROMs and diskettes are the slowest storage devices.
Drive Interface Standards
An important factor in determining how quickly a drive can read or write data is the
type of controller that the drive uses. A disk controller connects the disk drive to the
computers bus enabling the drive to exchange data with other devices.
EIDE
Enhanced integrated drive electronics (EIDE) is an enhanced version of IDE. It is
a catch all term for drive interfaces based on this standard. Supports transfer rates of
33 MBps. The standard variants go by many different names including Fast IDE,
ATA, Fast ATA and more.
SCSI
Small computer system interface (SCSI) was originally developed as a way to
connect third party peripheral devices to mainframe computers. One way to think of
SCSI is as an extension to the computers bus. As such all interface circuitry needed
by the device has to be on the device itself. One benefit is to improve efficiency,
allows higher transfer rates than EIDE.

Multimedia devices
1) computer
2) monitor
4) keyboard
touch pad
2) video card
3) soundcard
4) speakers
6) microphone
1) printer
2) scanner
CD-R/CD-RW drive)
4) modem
5) USB flash drive
6) webcam
7) digital camera
9) camcorder
Solution
Multimedia devices
1) computer
2) monitor

4) keyboard
touch pad
2) video card
3) soundcard
4) speakers
6) microphone
1) printer
2) scanner
CD-R/CD-RW drive)
4) modem
5) USB flash drive
6) webcam
7) digital camera
9) camcorder
Floppy disk working mechanism
Floppy disks work in a similar manner to cassette tapes and the magnetic strip on a credit card.
The floppy disk is constructed of stur plastic that is embedded with a thin iron oxide coating on
both sides. The head of the floppy disk drive easily manipulates the magnetic coating on the disk
to store information. Information is recorded on circular tracks and triangular sections. A special
head in the drive erases the area to be written before recording occurs. This head is wider than
the head used for recording and reading information to ensure recorded information is not
contaminated from previous information recorded nearby.
When reading the disk, the head moves to the appropriate track and sector quickly without
touching the disk. This is an improvement over older cassette tape storage that required a rewind
or fast forward movement to retrieve information. Floppy disks contain a safety slide on the side
of the case. If the slide is moved to create an opening, the drive will not record on the disk.
Introduction
A peripheral is a piece of computer hardware that is added to a computer in order to expand its
abilities. The term peripheral is used to describe those devices that are optional in nature, as

opposed to hardware that is either demanded or always required in principle. There are all
different kinds of peripherals you can add your computer. The main disctinction among
peripherals is the way they are connected to your computer. They can be connected internally or
externally.
Buses
A bus is a subsystem that transfers data between computer components inside a computer or
between computers. Unlike a point-to-point connection, a bus can logically connect several
peripherals over the same set of wires. Each bus defines its set of connectors to physically plug
devices, cards or cables together. There are two types of buses: internal and external. Internal
buses are connections to various internal components. External buses are connections to various
external components. There are different kinds of slots that internal and external devices can
connect to.
Internal
Types of Slots
There are many different kinds of internal buses, but only a handful of popular ones. Different
computers come with different kinds and number of slots. It is important to know what kind and
number of slots you have on your computer before you go out and by a card that matches up to a
slot you don’t have.
PCI
PCI (Peripheral Component Interconnect) is common in modern PCs. This kind of bus is being
succeeded by PCI Express. Typical PCI cards used in PCs include: network cards, sound cards,
modems, extra ports such as USB or serial, TV tuner cards and disk controllers. Video cards
have outgrown the capabilities of PCI because of their higher bandwidth requirements.
PCI Express
PCI Express was introduced by Intel in 2004. It was designed to replace the general-purpose PCI
expansion bus and the AGP graphics card interface. PCI express is not a bus but instead a point-
to-point conection of serial links called lanes. PCI Express cards have faster bandwidth then PCI
cards which make them more ideal for high-end video cards.
PCMCIA
PCMCIA (also referred to as PC Card) is the type of bus used for laptop computers. The name
PCMCIA comes from the group who developed the standard: Personal Computer Memory Card
International Association. PCMCIA was originally designed for computer memory expansion,
but the existence of a usable general standard for notbeook peripherals led to many kinds of
devices being made available in this form. Typical devices include network cards, modems, and
hard disks.
AGP

AGP (Accelerated Graphics Port) is a high-speed point-to-point channel for attaching a graphics
card to a computer’s motherboard, primarily to assist in the acceleration of 3D computer
graphics. AGP has been replaced over the past couple years by PCI Express. AGP cards and
motherboards are still available to buy, but they are becoming less common.
Types Of Cards
Video Card
A video card (also known as graphics card) is an expansion card whose function is to generate
and output images to a display. Some video cards offer added functions, such as video capture,
TV tuner adapter, ability to connect multiple monitors, and others. Most video cards all share
similar components. They include a graphics processing unit (GPU) which is a dedicated
microprocessor optimized for 3D graphics rendering. It also includes a video BIOS that contains
the basic program that governs the video card’s operations and provides the instructions that
allow the computer and software to interface with the card. If the video card is integrated in the
motherboard, it may use the computer RAM memory. If it is not it will have its own video
memory called Video RAM. This kind of memory can range from 128MB to 2GB. A video card
also has a RAMDAC (Random Access Memory Digital-to-Analog Converter) which takes
responsibility for turning the digital signals produced by the computer processor into an analog
signal which can be understood by the computer display. Lastly, they all have outputs such as an
HD-15 connector (standard monitor cable), DVI connector, S-Video, composite video or
component video.
Sound Card
A sound card is an expansion card that facilitates the input and output of audio signals to/from a
computer under control of computer programs. Typical uses for sound cards include providing
the audio component for multimedia applications such as music composition, editing video or
audio, presentation/education, and entertainment. Many computers have sound capabilities built
in,, while others require additional expansion cards to provide for audio capability.
Network Card
A network card is an expansion card that allows computers to communicate over a computer
network. It allows users to connect to each other either by using cables or wirelessly. Although
other network technologies exist, Ethernet has achieved near-ubiquity for a while now. Every
Ethernet network card has a unique 48-bit serial number called a MAC address, which is stored
in ROM carried on the card. You can learn more about networking in the introduction to
networking lesson.
external
Types of Connections
USB

USB (Universal Serial Bus) is a serial bus standard to interface devices. USB was designed to
allow many peripherals to be connected using a single standardized interface socket and to
improve the plug-and-play capabilities by allowing devices to be connected and disconnected
without rebooting the computer. Other convient features include providing power to low-
consumption devices without the need for an external power supply and allowing many devices
to be used without requiring manufacturer specific, individual device drivers to be installed. USB
is by far the dominating bus for connecting external devices to your computer.
Firewire
Firewire (technically known as IEEE 1394 and also known as i.LINK for Sony) is a serial bus
interface standard for high-speed communications and isochronous real-time data transfer,
frequently used in a personal computer. Firewire has replaced Parallel ports in many
applications. It has been adopted as the High Definition Audio-Video Network Alliance (HANA)
standard connection interface for A/V (audio/visual) component communication and control.
Almost all modern digital camcorders have included this connection.
PS/2
The PS/2 connector is used for connecting some keyboards and mice to a PC compatible
computer system. The keyboard and mouse interfaces are electrically similar with the main
difference being that open collector outputs are required on both ends of the keyboard interface
to allow bidirectional communication. If a PS/2 mouse is connected to a PS/2 keyboard port, the
mouse may not be recognized by the computer depending on configuration.
Devices
Removable Storage
The same kinds of CD and DVD drives that could come built-in on your computer can also be
attached externally. You might only have a CD-ROM drive built-in to your computer but you
need a CD writer to burn CDs. You can buy an external CD writer that connects to your USB
port and acts the same way as if it was built-in to your computer. The same is true for DVD
writers, Blu-ray drives, and floppy drives. Flash drives have become very popular forms of
removable storage especially as the price of flash drives decreases and the possible size for them
increases. Flash drives are usually USB ones either in the form USB sticks or very small,
portable devices. USB flash drives are small, fast, removable, rewritable, and long-lasting.
Storage capacities range from 64MB to 32GB or more. A flash drive does not have any
mechanically driven parts so as opposed to a hard drive which makes it more durable and smaller
usually.
Non-removable Storage
Non-removable storage can be a hard drive that is connected externally. External hard drives
have become very popular for backups, shared drives among many computers, and simply

expaning the amount of hard drive space you have from your internal hard drive. External hard
drives come in many shapes and sizes like flash drives do. An external hard drive is usually
connected by USB but you can also have a networked hardrive which will connect to your
network which allows all computers on that network to access that hard drive.
Input
Input devices are absolutely crucial to computers. The most common input devices are mice and
keyboards which barely every computer has. A new popular pointing device that may eventually
replace the mouse is touch screen which you can get on some tablet notebooks. Other popular
input devices include microphones, webcams, and fingerprint readers which can also be built in
to modern laptops and desktops. A scanner is another popular input device that might be built-in
to your printer.
Output
There are lots of different kinds of output devices that you can get for your computer. The
absolute most common external output device is a monitor. Other very popular output devices
are printers and speakers. There are lots of different kinds of printers and different sizes of
speakers for your computer. Monitors are connected usually through the HD-15 connector on
your video card. Printers are usually connected through a USB port. Speakers have their own
audio out port built-in to the sound card.
Types of Storage Devices
Physical components or materials on which data is stored are called storage media.Hardware
components that read/write to storage media are called storage devices.
Two main categories of storage technology used today are magnetic storage and optical storage.
Primary magnetic storage
o Diskettes
o Hard disks (both fixed and removable)
o High capacity floppy disks
o Disk cartridges
o Magnetic tape
Primary optical storage
o Compact Disk Read Only Memory (CD ROM)
o Digital Video Disk Read Only Memory (DVD ROM)
o CD Recordable (CD R)
o CD Rewritable (CD RW)
o Photo CD
Magnetic Storage Devices
Purpose of storage devices à to hold data even when the computer is turned off sothe data can be

used whenever needed. Storage involves writing data to the medium and reading from the
medium. Writing data à recording the data on the surface of the disk where it is stored for later
use. Reading data à retrieving data from thesurface and transferring it into the computers
memory for use.
Diskette drives, hard drives and tape drive all use the same type of medium à use similar
techniques for reading/writing data. Surfaces of diskettes and magnetic tape
are all coated with a magnetically sensitive material such as iron oxide.
The principle use to store data is that of polarisation – all the ions in the magnetic
material align themselves in one direction. Just as a transistor can represent binary
“on” or “off”, the orientation of the magnetic field can be used to represent data. A
magnet has one important advantage over a transistor à it can maintain it’s state
without a continual supply of electricity.
Surfaces of disks are coated with millions of tiny iron particles so data can be stored
on them. Each particle acts as a magnet, taking on a magnetic field when subjected to
an electromagnet. The read/write heads of a disk drive contain electromagnets, which
generate magnetic fields in the iron on the storage medium as the head passes over the
disk. The read/write heads store a string of 1s and 0s by alternating the direction of
the current in the electromagnet.
To read data the process is reversed. The read/write heads pass over the disk while no
current is flowing through the electromagnet. The storage medium has a charge and
the electromagnet does not à storage medium changes the magnet in the head which
causes a small current to flow through the head in one direction or the other
depending on the polarity of the field. The disk drive senses direction of flow and
data is sent from the head into memory.
Magnetic Disks
Diskette drives and hard disk drives are the most commonly used storage devices in
PCs. Both fall into the magnetic storage category because they record data as
magnetic fields.
Fundamental differences and similarities between the two:
· A diskette contains a single flat piece of plastic (the disk) coated with iron
oxide enclosed in vinyl or plastic cover. A hard disk contains one or more
rigid metal platters coated with iron oxide permanently enclosed in a hard disk
drive.
· Diskettes are small and portable (they can be removed from diskette drives).
Hard disks are usually built into the computer and are not portable (unless the
computer is). Exceptions are removable hard disks and external hard drives

which can be detached from the system.
· Floppy disks store only 1.44 MB although special floppy disks offer higher
capacity. New hard disks can store several thousand times as much data as a
diskette.
· Hard drives are much faster than diskettes, their disks spin faster and they
locate data on the disks surface in much less time.
Almost all PCs sold today come with a hard disk and one disk drive. Some computers
also feature a third built in magnetic device – a device that uses high capacity floppy
disks.
How data is organised on a magnetic disk
Before the computer can use a diskette to store data, the disks surface must be
magnetically mapped so that the computer can go directly to a specific point without
searching through all the data. This process of mapping a disk is called formatting or
initialising. When you purchase a new disk, they should be formatted for either PC or
Mac.
It may be helpful to reformat disks from time to time as this deletes all the data on
disk. During the formatting you process you can also determine whether the disk has
any faulty spots and you can copy important system files onto the disk.
Hard disks must also be formatted so that the computer can locate data on them.
When you buy a computer, the hard disk has already been formatted correctly and
probably contains some programs and data. You can format your hard disk if
necessary but the process is different to that for a diskette.
Modern diskettes store data on both sides of the disk (numbered side 0 and side 1) and
each side has its own read/write head. When formatting a disk, the disk creates a set
of magnetic concentric circles called tracks, on each side of the disk. The number of
tracks required depends on the type of disk. Most high -density diskettes have 80
tracks on each side. A hard disk may have several hundred tracks on each side of
each platter. Each track is a separate circle. These are numbered from the outermost
circle to the innermost, starting with zero.
Each track on a disk is also split into smaller parts. Imagine slicing a disk as you
would a pie. Each slice cuts across all the tracks resulting in short segments or
sectors. A sector can contain up to 512 bytes. All the sectors are numbered in one
long sequence so the computer can access each small area on the disk with a unique
number. This scheme simplifies a 2 dimensional set of co-ordinates into a single
numeric address.
If the diskette has 80 tracks on each side and each track contains 18 sectors à 1440

sectors per side à 2880 sectors per disk. This configuration is true regardless of the
length of the track. The diskettes outermost track is longer than the innermost one but
each track is still divided into the same number of sectors. Regardless of physical size
all the sectors hold the same number of bytes i.e. the shortest, innermost sectors hold
the same amount of data as the longest outermost ones.
A disks allocation of sectors per track is somewhat wasteful because the outer longer
tracks could theoretically hold more data than the shorter inner ones. For this reason
hard disks allocate more sectors to the longer tracks on the disks surface. As you
move towards the disks centre, each subsequent track has fewer sectors. This
arrangement takes advantage of the hard disks potential capacity and enables a typical
hard disk to store data more efficiently than a floppy disk. Because many hard disks
allocate sectors in this manner, their sectors per track specification are often given as
an average. Such hard disks are described as having an average of x sectors per track.
Because files are not usually a size that is an even multiple of 512 bytes, some sectors
contain unused space after the end of the file. In addition the Windows OS allocates a
group of sectors called a cluster to each file stored on a disk. Cluster sizes vary on
the size and type of disk, but can range from 4 à 64 sectors. A small file that
contains only 50 bytes will only use a portion of the first sector of a cluster leaving
the remainder of the sector and cluster allocated but unused.
The different capacities of disks are generally a function of the number of sides,
tracks and sectors per track. Floppy disks have only a few standard types and formats
but hard disks come in a variety of sizes so their capacities vary greatly.
A sector is the smallest unit with which any disk drive can work. Each bit and byte
within a sector can have different values but the drive can read or write only whole
sectors at a time. If the computer needs to change just 1 byte out of 512 it must
rewrite the whole sector.
How the OS finds data on a disk
A computer's Operating system can locate data on a disk because each track and
sector is labelled, and the location of all data is kept in a special log on the disk. The
labelling of tracks and sectors is called performing a logical format (also called low
level format or soft format). A commonly used logical format by windows creates 4
disk areas
1. Master boot record (MBR)
2. File – allocation table (FAT)
3. Root folder or directory
4. Data Area

Master boot record is a program that runs when you first start the computer. It
determines whether the disk has the basic components necessary to run the operating
system correctly. If the program determines that the correct files are present and disk
has a valid format, it transfers control to one of the OS programs that continues the
system start up (known as booting). Boot record also describes characteristics such
as number of bytes per sector and number of sectors per track.
FAT is a log that records the location of each file and the status of each sector. When
you write to a disk, the OS checks the FAT for an open area, stores the data and then
identifies the file and its location in the FAT. The FAT solves a common filing
problem, what happens when you load a file; increase its size by adding to it and then
save it again? The OS checks the FAT for free areas and places pointers that in it that
links together the nonadjacent parts of the file. In other words it splits the file by
allocating new space for the overflow, the pointers in FAT enable the OS to put the
file back together again.
When a file is saved in this way it becomes fragmented. Fragmented files cause side
effects such as taking longer to save and load.
Users do not see the information in FAT but often use the information. A folder (also
called a directory) is a tool for organising files on a disk. Folders can contain files or
other files so it is possible to set up hierarchical systems of folders on your computer.
The top folder on any disk is called the root folder (or root directory). When you
use the OS to view the contents of a folder, the OS lists specific information about
each file in the folder such as name, size, date of creation or last modification and so
on.
The part of the disk that remains free after the boot sector, FAT and root folder have
been created is called the data area, because that is where the data is stored!
Diskettes (Floppy Disks)
The diskette drive includes a motor that rotates the disk on a spindle and the
read/write heads that can move to any spot on the surface of the disk as it spins. This
allows the heads to access data randomly rather than sequentially – the heads can skip
from one spot to another without having to scan through all the data in between.
Diskettes spin at approx. 300 revolutions per minute. The longest it can take to
position a point on the diskettes under the read/write heads is the amount of time for
one revolution – 0.2 second. The farthest the heads have to move is from the centre
of the diskette to the outside edge (or vice versa). The heads can do this in less time –
about 0.17 seconds.
Because both operations occur at the same time (spinning the disk and moving the

heads over the surface), the maximum time to position the heads over a given location
on the diskette – known as maximum access time – remains the greater of the two
times, 0.2 second.
The maximum access time for diskettes can be even longer, however, because they do
not spin when they are not being used. It can take about 0.5 second to rotate the disk
from a dead stop.
Most common uses for disks
· Moving files between computers not connected by a network or
communication hardware – one of the easiest ways to move data from one
computer to another is to copy it onto diskette and use the diskette in another
computer.
· Loading new programs onto a system – Large programs are usually delivered
by CD-ROM but many programs are still sold on diskette. You install it by
copying the contents of the disks onto the hard drive and then running a small
program, which installs the files automatically.
· Backing up data or programs – Primary copy of data or programs are stored
on the hard drive, Backing up is the process of creating a duplicate copy for
safekeeping. To protect against data loss it is wise to back up a hard disk.
Due to the limited storage capacity diskettes are used to back up small data
files rather than programs or entire hard disks.
Types of Diskettes
1980’s à most PCs used 5.25-inch diskettes.
Now à almost completely replaced by the 3.5-inch.
The size refers to the diameter of the disk and is not an indication of capacity.
The 5.25 type is encased in a flexible vinyl envelope with an oval cutout that allows
read/write heads access to the disk. The 3.5 type is encased in a hard plastic shell
with a sliding shutter. On insertion into the drive the shutter slides back to expose the
surface to the read/write heads.
Diskette capacities
Both types have evolved from lower to higher densities. The density is a measure of
the capacity of the surface of the disk, the higher the density à the more closely the
iron oxide particles are packed à the more data a disk can store.
Early versions of disks were double density (DD). As diskette media improved à
storage capacity improved. DD diskettes have been replaced by high density (HD)
ones providing significantly more storage.
Diameter Sectors/ Bytes/ Total

(inches) Type Tracks track Sectors sector bytes
5.5 DD 40 9 720 512 360k
5.5 HD 80 15 2400 512 1200k
3.5 HD 80 9 1440 512 720k
3.5 HD 80 18 2880 512 1440k
3.5 HD 80 36 5760 512 2880k
Macs never used 5.25 diskettes.
DD Mac disk holds 800k not 720k.
The Extra density disk holds more data than a regular 1.44 MB disk but needs a
special hard drive.
Hard Disks
Hard disk is still the most common storage device for all computers. Like diskettes
hard drives store data in tracks divided into sectors. Physically however they look
quite different to diskettes.
Includes one or more metal platters mounted on a central spindle, like a stack of rigid
diskettes. Each platter is covered with a metal coating and the entire unit is contained
in a sealed chamber. The hard disk and drive are a single unit which includes the hard
disk, the motor that spins the platters and a set of read/write heads. Because you
cannot remove the disk from the drive the terms hard disk and hard drive are used
interchangeably.
Hard drives have become the primary storage devices for PCs because they are
convenient and cost effective. They outperform diskettes in both speed and capacity.
Hard disks offer capacities from several hundred MB and more. Most entry level PCs
now come with hard disks of at least 6.8MB.
Two important physical differences between hard disks and diskettes account for the
differences in performance.
1. Hard disks are sealed in a chamber
2. Hard disk consists of a rigid metal platter (usually aluminium) rather than
flexible Mylar.
Hard disk spin between 3600 rpm and 7200 rpm compared to a diskette 300 rpm. The
speed at which the disk spins is a major factor in overall performance. The rigidity of
the disk and the high-speed rotation allows more data to be recorded on the surface.
Waving a magnet past an electric coil causes a current to flow. The faster you wave
the magnet and the closer the magnet is to the coil, the larger the current generated in
the coil. The disk that spins faster can use smaller magnetic charge to make current
flow to the read/write head. The drives heads can also use a lower density current to

record data on the disk.
Not only do hard disks pack the data closer together they also hold more data because
they usually include multiple platters stacked one on top of each other. This
configuration means that the disk has more than 2 sides, in addition to side 0 and 1
there are sides 2, 3, 4, and so on. Larger capacity disks may use 12 platters but both
side of every platter are not always used.
The number of sides that the disk uses is specified by the number of read/write heads.
A particular disk may have 6 disks platters (12 sides) but only 11 heads à one side is
not used to store data. Unused side is often the bottom one.
The term cylinder is often used to refer to the same track across all the disks. Track 0
(outermost track) on every disk is cylinder 0.
Hard disk generally store 512 bytes of data in a sector, but can have more sectors per
track – 54, 63 or even more sectors per track are not uncommon.
Computation of a hard disks capacity is identical to that for other disks but the
numbers are larger. Breakdown of capacity for a 50 GB hard disk, assuming 11
platters, 264,528 tracks, 369 sectors per track:
12024 cylinders x 22 heads (sides)
= 264528 tracks
264528 tracks x 369 avg. sectors/track
= 97,610,823 sectors
97610823 sectors x 512 bytes
=49,976,754,984 bytes
(Approx)
If the actual numbers of sectors per track were taken into account instead of an
average, the calculation would be more difficult and the resulting number of bytes
would be higher.
In spite of capacity and speed advantages there is one major drawback à to achieve
optimum performance the read/write heads must be extremely close to the surface of
the disk without actually touching it. The read/write heads fly so close to the disk that
a human hair, a dust particle or even a fingerprint would bridge the gap and cause the
head to crash. A head crash – in which the head touches the disk – can destroy the
data stored in the area of the crash. A severe head crash can destroy the read/write
head.
Removable high capacity magnetic disks
· High capacity floppy disks
Disks with the same dimensions as 3.3-inch floppy diskette or slightly larger

have a much greater capacity than a standard diskette. Popular high capacity
floppy disks include
1. A HiFD - (high capacity floppy drive) made by Sony Electronics Inc.
Looks like a normal 3.5-inch disk but can store up to 20 MB. This
drive can read and format double density and high-density floppy disks
in addition to HiFD disks.
2. SuperDisk – made by Imation, same dimensions as standard 3.5-inch
but formatted to hold 120 MB. Drives are compatible with highdensity
3.5-inch diskettes.
3. Zip Disks – made by Iomega Corp. Available in 100 MB and 250 MB
capacities and require a special disk drive and utility software. Slightly
larger than normal and are not compatible with ordinary floppy.
· Hot-Swappable Hard Disks
At the high end of price and performance. Sometimes used on high-end
workstations or servers that require large amounts of storage. They allow the
user to remove (swap out) a hard disk and insert (swap in) another while the
computer is still on (hot). The removable disk contains the disk, drive and
read/write heads in a sealed box.
· Disk Cartridges
Most removable disks work like a diskette, a disk in a plastic case that is
inserted into or removed from the drive. The disk and case are called disk
cartridges. Do not offer the same storage as true hard disks, they hold more
data than diskettes and are faster and just as portable.
Tape Drives
Read and write data to the surface of a tape the same way as an audiocassette –
difference is that a computer tape drive writes digital data.
Best use of tape storage is for data that is not used often, such as backup copies of
your hard disk. Because a tape is a long strip of magnetic material, the tape drive has
to write the data to it serially – 1 byte after another. This is inherently slower than the
direct access provided by media such as disks. When you want to assess specific data
on a tape the drive has to scan through all he data that you don’t need to get to the
data that you want. Result à Slow access time. The access time varies depending on
the speed of the drive, length of tape and position on the tape to which the head wrote
the data in the first place.
Despite the long access time tape drives are well suited for certain purposes –
especially backing up a systems entire hard disk. Backing up using high capacity

disks or disk cartridges is usually expensive. Many people now use recordable CDs
to back up their system. This option is more expensive than tapes, and unless CDRW
are used the data cannot be overwritten. Capacities of tapes can be as high as 100
GB and more, tape offers an inexpensive way to store a lot of data on a single
cassette.
Special type of tape drive uses digital audiotape (DAT) to achieve high storage
capacities. DAT drives typically have multiple read and write heads built into a small
wheel or cylinder that spins near the tape at high speed. The tape moves past the
heads with a slower speed. The write heads on the spinning wheel each write the data
with opposite magnetic polarities on overlapping areas of the tape. Each read head
reads only one polarity or the other. The result is a high density per inch of tape.
Although DAT tapes are relatively inexpensive the drives can be expensive when
compared to standard tape drives.
Optical Storage Devices
The most popular alternative to magnetic storage systems are optical storage media.
The most widely used type of optical storage medium is the compact disk (CD),
which is used in CD-ROM, DVD-ROM, CDR, CDRW and PhotoCD systems.
Since the mid 1990s nearly all PCs have been sold with a built in CD-ROM drive.
Consumers are now buying more systems with DVD-ROM drives rather than
standard CD-ROM units. These devices fall into the optical storage category because
they store data on a reflective surface so that it can be read by a beam of laser light. A
laser uses concentrated, narrow beam of light, focused and directed with lenses,
prisms and mirrors. The tight focus of the laser beam is possible because all the light
is of the same wavelength.
CD-ROM
The familiar audio compact disk is a popular medium for storing music. In the
computer world, the medium is called compact disk read only memory (CD-ROM).
This uses the same technology used to produce music CDs.
The CD-ROM drive for music or data reads 0s and 1s from a spinning disk by
focusing a laser on the disks surface. Some areas of the disk reflect the laser light into
a sensor, other areas scatter the light. A spot that reflects the laser beam is interpreted
as a 1 and the absence of a reflection is interpreted as a 0.
Data is laid out on a CD-ROM disk in a long, continuous spiral that starts at the outer
edge and winds inwards towards the centre. Data is stored in the form of lands,
which are flat areas on the metals surface, and pits, which are depressions or hollows.
A land reflects the laser light into the sensor (a data bit of 1) and a pit scatters the light

(a data bit of 0).
On a full CD-ROM the spiral of data stretches almost 3 miles long. A standard CD
can store 650 MB of data or about 70 mins of audio.
CD-ROM Speeds
Compared to hard disk drives CD-ROM drives are quite slow, in part because the
laser reads pits and lands one bit at a time. Another reason is the rotational speed of
the disk. Like a track on a magnetic disk the track of an optical disk is split into
sectors. However the sectors are laid out quite differently than they are on magnetic
disks.
The sectors near the middle of the CD wrap farther around the disk than those near the
edge. For the drive to read each sector in the same amount of time it must spin the
disk faster when reading the sectors near the middle and slower when reading the
sectors near the edge. Changing the speed of rotation takes time – enough to seriously
impair the overall performance of the CD-ROM drive. The first CD-ROM drives read
data at 150 KBps and were known as single speed drives. This rate is much slower
than that of a typical hard drive which transfers data at rates of 5 – 15 MBps.
Presently CD-ROM drives read data 2 à 52 times faster than first models (300 à
7800 KBps).
Even with the changing speed of the disk reading data from an optical medium is a
relatively simple undertaking. Writing data however is another matter. The medium
is a foil disk that is physically pitted to reflect or scatter the laser beam. The disk is
then covered in a plastic coating and it is difficult to alter the surface of the disk after
it has been stamped.
CD-ROM Uses
The fact that you must use special technologies to write data to an optical disk does
not mean that this storage medium is not useful. In fact many applications rely on
huge volumes of data that rarely change. Because of the high precision and data
density possible with CD-ROM, a single CD typically can hold about 650 MB of data.
Software companies can distribute their products on CD-ROM. Because of the high
capacity and the fact that 1 CD much cheaper to produce than a set of diskettes, many
software publishers regard CDs as the distribution medium of choice.
DVD-ROM
Digital video (or versatile) disk read only memory, is a high-density medium capable
of storing a full-length movie on a single disk the size of a CD.
Achieves such high storage capacities by using both sides of the disk and special data
compression technologies. The latest generation of DVD-ROM use layers of data

tracks; the laser beam reads data from the first layer and then looks through it to read
data from the second layer.
Each side of a standard DVD-ROM can hold up to 4.7 GB. Dual layer DVD-ROM
can hold 17 GB of data.
CD-R, CD-RW, PhotoCD
CD-R allows you to create your own CD-ROM disks that can be read by any CDROM
drive. After the information has been written to the CD it cannot be changed.
Using CD-RW drives the user can write and overwrite data onto CDs. With a CDRW
data can be revised in the same manner as a floppy disk.
One popular form of recordable CD is PhotoCD, a standard developed by Kodak for
storing digitised photographic images on a CD. Many film-developing stores now
have PhotoCD drives that can store your photos and put them onto a CD.
Measuring Drive Performance
Average Access Time
For a storage device the average access time (or seek time ) is the amount of time the
device takes to position its read/write heads over any spot in the medium. This
measurement is an average because access times can vary greatly depending on the
distance between the heads original location and their destination.
For storage devices access times are measured in milliseconds (ms). For memory
devices access times are measured in nanoseconds (ns).
In a disk drive the access time depends on a combination of 2 factors.
1. Revolutions per minute (rpm).
2. Time taken to move the heads from one track to another.
Device Typical Access Time
Static RAM (SRAM) 5 – 15 ns
Dynamic RAM (DRAM) 50 – 70 ns
ROM 55 – 250 ns
Hard disk drives 6 – 12 ms
CD-ROM drives 80 – 800 ms
Tape Drives 10 – 500 s
File Compression
One solution to the storage problem is to compress data. File compression or data
compression is the technology for shrinking the size of a file, thereby freeing up
space for more data and programs to reside on the disk.
Entire hard disks, floppy disks, or individual files can be compressed as much as a 3:1
ratio. File compression is performed by software that uses mathematical algorithms

to squeeze the data into smaller chunks by removing information that is not vital to
the file or data. When the file is returned to its original size this data is reinserted so
that the original data is reproduced exactly as it was before compression.
A utility used to compress one or more files shrinks the selected files and stores them
inside a new file with its own name. The resulting file is called an archive file
because it stores the compressed data inside.
Data transfer rate
The speed at which a device can transfer data – how long it takes for one device to
transfer data to another device. Speeds are expressed as a rate, or as some amount of
data per unit time. When measuring a devices data transfer rate (throughput) the
time is measured in seconds, but units of data may be measured in bytes, KB, MB or
GB.
Speeds for hard disks are generally high, from around 15 MBps to 80 MBps and
higher. CD-ROMs and diskettes are the slowest storage devices.
Drive Interface Standards
An important factor in determining how quickly a drive can read or write data is the
type of controller that the drive uses. A disk controller connects the disk drive to the
computers bus enabling the drive to exchange data with other devices.
EIDE
Enhanced integrated drive electronics (EIDE) is an enhanced version of IDE. It is
a catch all term for drive interfaces based on this standard. Supports transfer rates of
33 MBps. The standard variants go by many different names including Fast IDE,
ATA, Fast ATA and more.
SCSI
Small computer system interface (SCSI) was originally developed as a way to
connect third party peripheral devices to mainframe computers. One way to think of
SCSI is as an extension to the computers bus. As such all interface circuitry needed
by the device has to be on the device itself. One benefit is to improve efficiency,
allows higher transfer rates than EIDE.
Multimedia devices
1) computer
2) monitor
4) keyboard

touch pad
2) video card
3) soundcard
4) speakers
6) microphone
1) printer
2) scanner
CD-R/CD-RW drive)
4) modem
5) USB flash drive
6) webcam
7) digital camera
9) camcorder

Main components of a computerMultimedia devicesOther peripheral .pdf

More Related Content

Similar to Main components of a computerMultimedia devicesOther peripheral .pdf (20)

More from venkt12345 (20)

Recently uploaded (20)

Main components of a computerMultimedia devicesOther peripheral .pdf