ROM

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Ashish Asati (21) Ravitesh mishra
Atul Sen (26) A.P.
Amit Kumar (09)
Anurag Parmar (18)
Ashish Yadav (26)

April 3, 2013 1

MEMORY
 Internal storage areas in the computer.
 There is two types of memory–
1)volatile 2)non volatile
 Volatile memory retains the information as long as power supply is on, but when
power supply is off or interrupted the stored memory is lost
 Nonvolatile memories that can retain stored information even when not powered

April 3, 2013 2

Read only memory
Built into every computer is one or more chips that store program code which
provides the basic input output functions for the system . designed to power on
the system, perform basic hardware tests (POST) and bootstrap the system.

April 3, 2013 5

Why we use ROM
ROM- Read Only Memory. The CPU cannot easily write information into ROM, it
is generally programmed upon manufacture with particular data. A program will
be stored on ROM, the CPU will read ROM and carry out tasks dictated by the
data it reads
RAM - Random Access Memory is used by the CPU to store and retrieve
information. It is writeable and readable. used as a temporary storage for
calculations in a similar way we would use paper.

April 3, 2013 6

Difference Between RAM and ROM
The main difference between RAM and ROM is their use. ROM is used
to store the code for programs that are run in the processor.
In comparison, RAM is used to hold the temporary data that is
created and used by the program.

April 3, 2013 7

Types of ROM
MROM
PROM
EPROM
EEPROM
EAROM
NAND ROM

April 3, 2013 8

MROM
PROM
EPROM
EEPROM
EAROM
NAND ROM

April 3, 2013 9

MASK ROM

To produce Mask ROM (MROM) chips, integrated circuits (ICs) are
masked during the design phase of the semiconductor fabrication
process
mask read-only memory (ROM) is a cost-effective alternative to
programmable read-only memory (PROM)

April 3, 2013 10

MROM
PROM
EPROM
EEPROM
EAROM
NAND ROM

April 3, 2013 11

Programmable ROM (PROM):
This is a type of ROM that can be programmed using special equipment; it can be
written , but only once. This is useful for companies that make their own
ROMs from software they write, because when they change their code they
can create new PROMs without requiring expensive equipment.
This is similar to the way a CD-ROM recorder works by letting you "burn"
programs onto blanks once and then letting you read from them many times.
In fact, programming a PROM is also called burning, and it is comparable in
terms of its flexibility.

April 3, 2013 12

MROM
PROM
EPROM
EEPROM
EAROM
NAND ROM

April 3, 2013 13

Erasable Programmable ROM (EPROM)
An EPROM is a ROM that can be erased and reprogrammed. A little glass window
is installed in the top of the ROM package, through which you can actually see
the chip that holds the memory.
Ultraviolet light of a specific frequency can be shined through this window for a
specified period of time, which will erase the EPROM and allow it to be
reprogrammed again. Obviously this is much more useful than a regular PROM,
but it does require the erasing light.

April 3, 2013 14

MROM
PROM
EPROM
EEPROM
EAROM
NAND ROM

April 3, 2013 15

Electrically Erasable Programmable ROM (EEPROM)
The next level of erasability is the EEPROM, which can be erased under software
control. This is the most flexible type of ROM, and is now commonly used for
holding BIOS programs. When you hear reference to a "flash BIOS“ or doing a
BIOS upgrade by "flashing", this refers to reprogramming the BIOS EEPROM
with a special software program.
Here we are blurring the line a bit between what "read-only" really means, but
remember that this rewriting is done maybe once a year or so, compared to
real read-write memory (RAM) where rewriting is done often many times per
second!

April 3, 2013 16

MROM
PROM
EPROM
EEPROM
EAROM
NAND ROM

April 3, 2013 17

Electrically alterable read-only memory(EAROM)

It is a type of EEPROM that can be modified one bit at a time. Writing is a very
slow process and again needs higher voltage (usually around 12 V) than is used
for read access. EAROMs are intended for applications that require infrequent
and only partial rewriting. EAROM may be used as non-volatile storage for
critical system setup information; in many applications, EAROM has been
supplanted by CMOS RAM supplied by mains power and backed-up with
a lithium battery

April 3, 2013 18

MROM
PROM
EPROM
EEPROM
EAROM
NAND ROM

April 3, 2013 19

NAND ROM
It is a modern type of EEPROM invented in 1984. Flash memory can be erased
and rewritten faster than ordinary EEPROM, and newer designs feature very high
endurance. Modern NAND flash makes efficient use of silicon chip area, resulting
in individual ICs with a capacity as high as 32 GB as of 2007; this feature, along
with its endurance and physical durability, has allowed NAND flash to
replace magnetic in some applications (such as USB flash drives). Flash memory is
sometimes called flash ROM or flash EEPROM when used as a replacement for
older ROM types, but not in applications that take advantage of its ability to be
modified quickly and frequently.

April 3, 2013 20

Speed
Reading
Although the relative speed of RAM vs. ROM has varied over time, as of
2007 large RAM chips can be read faster than most ROMs. For this reason
(and to allow uniform access), ROM content is sometimes copied to RAM
or shadowed before its first use, and subsequently read from RAM.
Writing
For those types of ROM that can be electrically modified, writing speed is
always much slower than reading speed, and it may need unusually high
voltage, the movement of jumper plugs to apply write-enable signals, and
special lock/unlock command codes. Modern NAND Flash achieves the
highest write speeds of any rewritable ROM technology, with speeds as high
as 15 MB/s, by allowing (needing) large blocks of memory cells to be written
simultaneously.

April 3, 2013 21

Advantages
ROM is used to permanent and secure data storage.
A ROM chip is also non volatile so data stored in it is not lost when power is
turned off.
ROM cannot be reconfigured at all.
It is generally used to start your computer up and load the operating system.
The ROM is sustained by a small long-life battery in your computer.
If you ever do the hardware setup procedure with your computer, you effectively
will be writing to ROM.
ROM (in this sense the BIOS) runs self tests, detects and initializes hardware
devices and then loads the OS.

April 3, 2013 22

Disadvantages
One of the main disadvantages of Read-Only Memory is that a given system will
require about twice as long to read ROM information as it would the same
data stored as Random Access Memory.
To improve speed, many systems load frequently used files into RAM and read
from there when they are needed.

April 3, 2013 23

Summary

April 3, 2013 24

Two Writable Bits Universal

April 3, 2013 27

Conclusion
In error-free non-reversible ROM computing:
Quantum computers more space efficient than
their classical counterparts
 only requiring 1 writable qubit to be universal.
 Conjecture: Minimal QC can calculate certain
boolean functions exponentially faster than
the minimal classical ROM computer.

April 3, 2013 28

ROM

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