Computer system architecture

Computer system can be organized in a number of
can categorize roughly according to the number of
general-purpose processors used.
How a modern computer system works.

 The general-purpose processors are
categorized as follows.
1)Single-Processor Systems.
2)Multiprocessor Systems.
3) Clustered Systems.

Single-Processor Systems:
 Most computer systems used a single
processor.
 On a single processor system, there is one
main CPU capable of executing a general-
purpose instruction set,including
instructions from user processes.

Single-Processor Systems:
 Almost all single processor systems have
other special-purpose processors as well.
 They come in the form of device-specific
processors, such as disk, keyboard, and
graphics controllers.
 on mainframes, they may come in the form of
more general-purpose processors, such as
I/O processors that move data rapidly among
the components of the system

 All of these special-purpose processors run a
limited instruction set and do not run user
processes.
 They are managed by the operating system,
in that the operating systems ends them
information about their next task and
monitors their status.

 For example, a disk-controller
microprocessor receives a sequence of
requests fromthemain CPU and implements
its own disk queue and scheduling algorithm.
 This arrangement relieves the main CPU of
the overhead of disk scheduling.

 PCs contain a microprocessor in the keyboard to
convert the keystrokes into codes to be sent to
the CPU.
 In other systems or circumstances, special-purpo
se processors are low-level components built
into the hardware.
 The operating system cannot communicate with
these processors; they do their jobs
autonomously.
 The use of special-purpose microprocessors is
common and does not turn a single-processor
system into a multiprocessor.

Multiprocessor Systems:
 The multiple-processor systems in use
today are of two types.
1. Asymmetric multiprocessing.
2. Symmetric multiprocessing.
Asymmetric multiprocessing: in which each
processor is assigned a specific task.

Symmetric multiprocessing (SMP):
The most common systems use symmetric
multiprocessing (SMP), in which each
processor performs all tasks within the
operating system.

Multiprocessor Systems:
 multiprocessor systems also known as
parallel systems or multicore systems.
 Multiprocessor systems have two or more
processors in close communication, sharing
the computer bus and sometimes the clock,
memory, and peripheral devices.

 Multiprocessor systems first appeared
prominently appeared in servers and have
since migrated to desktop and laptop
systems.
 Recently, multiple processors have appeared
on mobile devices such as smart phones and
tablet computers.

 Multiprocessor systems have three main
advantages:
1)Increased throughput.
2)Economy of scale.
3)Increased reliability.

1.Increased throughput.
 By increasing the number of processors, we
expect to get more work done in less time.
 The speed-up ratio with N processors is not
N, however; rather, it is less than N.

Economy of scale.
 Multiprocessor systems can cost less than
equivalent multiple single-processor systems,
because they can share peripherals, mass
storage, and power supplies.
Increased reliability.
 If functions can be distributed properly
among
several processors,thenthe failure of one
processor will not halt thesystem, only slow it
down.

 If we have ten processors and one fails, then
each of the remaining nine processors can pick
up a share of the work of the failed
processor.
 Thus, the entire system runs only 10 percent
slower, rather than failing altogether.

Clustered Systems:
 Another type of multiprocessor system is a
clustered system, which gathers together
multiple CPUs.
 Like multiprocessor systems, but multiple
systems working together.
 Usually sharing storage via a storage-area network
(SAN)

Provides a high-availability service which survives
failures
 Asymmetric clustering has one machine in hot-
standby mode
 Symmetric clustering has multiple nodes running
applications, monitoring each other
Some clusters are for high-performance computing
(HPC)
 Applications must be written to use parallelization

 Some have distributed lock manager (DLM) to avoid
conflicting operations.

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Thank you………

Computer system architecture

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