Computer system

© SMT, Faculty, CSE, IUBAT

The procedure that transforms raw data into useful

information is called processing. This function is divided

between the computer's processor and memory.

The CPU - The processor is also called the central processing

unit (CPU). It manages all devices and performs the actual

processing of data.

The CPU consists of one or more chips attached to the

computer's main circuit board (the motherboard).

Memory - Memory also consists of chips attached to the

motherboard. Memory holds data and program instructions

as the CPU works with them. This memory is called Random

Access Memory (RAM). The CPU can find any piece of data

in RAM, when it needs it for processing.

Processing


The smallest usable unit of measure for memory is the byte – the

amount of memory required to hold one character, like the letter

A or the numeral 2. Computers work with larger chunks of data,

measured in multiple bytes, as shown below:

Processing

Unit Approx. Value Actual Value (bytes) (bytes) (bytes)

Kilobyte (KB) 1,000 B 1,024

Megabyte (MB) 1,000 KB 1,048,576

Gigabyte (GB) 1,000 MB 1,073,741,824

Terabyte (TB) 1,000 GB 1,099,511,627,776


How Computer Processes Data

The Control Unit (CU)

The Arithmetic Logic Unit (ALU)CPU

Memory Volatile

Nonvolatile

Flush

Cache

Bus

Registers

Address Bus

Data Bus

Control Bus

Devices that

affect

Processing

Speed

Devices that

affect

Processing

Speed



The Control Unit (CU):

All the computer’s resources are managed from the control unit.

This is the logical hub of the computer.

The Arithmetic Logic Unit (ALU):

Arithmetic operations include addition, subtraction, multiplication

and division. When the control unit encounters an instruction that

involves arithmetic or logic, it passes that instruction to ALU.

CPU



CPU needs to have millions of memory spaces to quickly read or write

programs and data while they are being used.

Non- Volatile:

Non-volatile chips hold data even when the computer is unplugged.

For example, ROM, PROM(Programmable Read Only Memory),

BIOS.

Volatile:Volatile memory requires power to store data. For example, RAM, SIMM,

DIMM, SO-DIMM.

Flush:Flush memory is a special type of non-volatile memory. It is often used as

portable storage device. Example, Digital camera, portable MP3 player, USB

device. On this devices data is stored using physical switches.

Memory



Memory

CPU needs to have millions of memory spaces to quickly read or write

programs and data while they are being used.

Cache:

Moving data between RAM and the CPU’s register is one of the

most time consuming task, as Ram is more slower than CPU. A

partial solution is to add a small memory with the CPU. It is similar

to RAM, but very fast. It holds common or recently used data

Speeds up computer processing. Most computers have several

caches.

When a program is running and CPU needs to read data, it first

checks whether the data is in the Cache memory. If the data is not

there, then CPU loads the data from RAM to registers and also,

loads a copy to the Cache.


This type of devices is used to tell the processor what must be done based on

the instructions in the memory written by users.

So if, for example, some bytes are found in the memory that corresponds to an

addition instruction the decoder will read them and knows that it is addition

based on the bytes contained then it will activate the control lines to inform the

processor that it is an addition.

Thus the decoder is considered an interface between the memory and the

processor


Decoders



The size of a register, which is sometimes called the word-size indicates the

amount of data or bits with which a processor can work at a single time. The

bigger the word size, the more quickly computer can process data.

In real life the terminologies “16-bit processor” or, “64-bit processor” is refers

to the size of registers in the processor. If other factors are kept normal, than

32-bit registers can process data twice as fast as the registers with 16-bits.

Registers

BUS is the electronic pathway between CPU components. Bus width is

measured in bits. Expansion bus connects to peripherals. System bus

connects CPU and RAM.

BUS



System Bus is of three types- Address bus, Data bus, Control bus.

BUS



While processing, Address bus and Data bus are used to sharing data

between RAM and CPU.

BUS





Address - the components pass memory addresses to one another over the address bus.

Control - used to send out signals to coordinate and manage the activities of the motherboard components.

Data - transferred between peripherals, memory and the CPU. Obviously, the data bus can be a very busy pathway.

BUS


How Computer Processes DataBUS

External Bus Standards-

– Industry Standard Architecture (ISA) : is a 16-bit data bus. Used to

connect modem and other slow devices.

– Local bus : is an internal system bus, that runs between components of

the motherboard.

– Peripheral control interface : ISA in present computer is being replaced

by PCI bus. PCI bus is designed by Intel to make it easier to integrate

new data types : audio, video, graphics, modems and sound cards.

– Accelerated graphics port (AGP): special architecture that enables

video cards to access system’s Ram directly. AGP improves graphics

quality. At present it is enhanced with 3D technology. Extremely fast

bus


– Universal serial Bus: Connects external devices. Hot swappable.

Allows up to 127 devices. Cameras, printers, and scanners

– IEEE 1394 (FireWire) : Mostly found in MACINTOSH computers and

used to integrate video devices, such as cameras and video cameras.

Many digital TV cameras also use FireWire.

– PC Card: Used exclusively in laptops. Most common use of PC cards

include Wi-Fi cards, network card, thumb scanner (for security) etc.


External Bus Standards-




Machine Cycle

Fetching

Decoding

Execution

Storing

CPU performance is dependent upon Instruction Count, CPI (Cycles per

instruction) and Clock cycle time. And all three are affected by the instruction

set architecture.

Machine Cycle

Steps by CPU to process data.

Fetching: This is the instruction

cycle. Here, CPU fetches the

instruction from memory to

registers.

Decoding: CPU breaks downs

the instructions to correspond

with the CPU’s instruction set.


Machine Cycle

Execution: CPU carries out the instructions in order.

Storing: Often CPU may required to store the outcome into the memory.


How Computer Processes DataProcessors

A processor is a type of microchip that is used to receive, process, and

send out instructions and commands. it is typically made of silicon and

other materials. Processors features are-

Speed of processor

Size of cache

Number of registers

Bit size

Speed of Front side bus



CISC Processor (Complex Instruction Set Computing)

Supplies a large number of complex instructions at the assembly language

level.

During the early years, memory was slow and expensive and the

programming was done in assembly language. Since memory was slow and

instructions could by retrieved up to 10 times faster from a local ROM than

from main memory, programmers tried to put as many instructions as possible

in a microcode.

The CISC approach attempts to minimize the number of instructions per

program, sacrificing the number of cycles per instruction.


RISC processors (Reduced Instruction Set Computing)

RISC does the opposite, reducing the cycles per instruction at the cost of

the number of instructions per program. It is a type of microprocessor that

has a relatively limited number of instructions.

It is designed to perform a smaller number of types of computer

instructions so that it can operate at a higher speed (perform more million

instructions per second, or millions of instructions per second).

Earlier, computers used only 20% of the instructions. Making the other

80% unnecessary. One advantage of reduced instruction set computers is

that they can execute their instructions very fast because the instructions

are so simple.



Standard computer ports

Keyboard and mouse ports

USB ports

Parallel

Network

Modem

Audio

Serial

Video

Extending The Processors Power


Serial and parallel ports

Connect to printers or modems

Parallel ports move bits simultaneously

• Made of 8 – 32 wires

• Internal busses are parallel

Serial ports move one bit

• Lower data flow than parallel

• Requires control wires

• UART converts from serial to parallel

Extending The Processors Power


Serial Communications


Parallel Communications


Thank You!


Education

Computer system