Computer Organization

• The digital computer is a digital system that performs various computational tasks

• Digital computer use binary number system which has two digits or states 0 and 1. A binary digit is called bit. Information in digital computer is represented by in group of bits. By using coding techniques group of bits can be made to represent not only binary numbers but also other discrete values such as decimal digits or letters of the alphabet

Digital computer

A computer system is divided into two functional entities • Hardware & • Software

The hardware of the computer system consists of all electronic components and elctromechnical devices that comprise the physical entity of the deviceComputer software consists of instructions and data that computer manipulates to perform various data processing tasks

Basic Terms related to Digital computerProgram : A sequence of instructions for the computer is called a

program.

Digital computer

Database: The data that are manipulated by the program constitute the databaseSystem Software: It consists of collection of programs whose purpose is to make effective use of the computer e.g. operating system. These system software are distinguished from application programs which are written for solving particular problem. E.g. An application program written in high level language is translated into machine language by the use of system program compiler or translator. In other words its function is to compensate the differences that exists between user needs and capability of the hardware.

Digital computer

The hardware of the computer is usually divided into three parts.The Central processing Unit: It contains arithmetic & Logic unit for manipulating data, a number of registers for storing data, and control circuits for fetching and executing instructions.

The memory of a computer contains storage for instructions and data. It is called random access memory because CPU can access any memory location at random and can retrieve information on fixed interval of time

The input and output processor contains electronic circuits for communicating and controlling the transfer of information between computer and outside world. Input Output devices consists of Keyboards , printers terminals and magnetic drives and other communicating devices.

Digital computer

Processor(CPU+CU)

Memory

Input-Output Processor (IOP)Input Unit Output Unit

Digital computer

Computer hardware (subsystems)

CENTRALPROCESSING

UNIT(CPU)

CENTRALPROCESSING

UNIT(CPU)

CPU

• Performs arithmetic and logical operations• Arithmetic operation– Unary: increment (+1) and decrement (-1)– Binary: add, subtract, multiply, and divide

• Logical operation– Unary: NOT– Binary: AND, OR, XOR

Central Processing Unit --Arithmetic logic unit

• Registers are fast storage locations that hold data temporarily.

• Data registers– Input data and output data

• Instruction registers• Program counter

Central Processing Unit --Registers

• The control unit is like the part of the human brain that controls the operation of each part of the body.

• Controlling is achieved through wires that can be on (hot) or off (cold).

Central Processing Unit –Control Unit

MAIN MEMORYMAIN MEMORY

Table :Memory units

Unit------------kilobyte

megabytegigabyteterabytepetabyteexabyte

Exact Number of bytes------------------------

210 bytes220 bytes230 bytes240 bytes250 bytes260 bytes

Approximation------------103 bytes106 bytes109 bytes1012 bytes1015 bytes1018 bytes

Main Memory

Main memory

• Address space: – the total number

of uniquely identifiable locations in memory

Memory addresses are defined usingunsigned binary integers.

Note:

Address as bit pattern

• RAM: random access memory– SRAM: static RAM• flip-flop gates • No need to be refreshed• Cache memory

– DRAM: dynamic RAM• capacitors • Need to be refreshed periodically• Main memory

Memory types-- RAM

• ROM: read-only memory– PROM: programmable ROM• Only written once

– EPROM: erasable PROM• Use ultraviolet light to erase data

– EEPROM: electronically EPROM• Can be erased using electronic impulses

Memory types-- ROM

Memory hierarchy

Cache memory

• Why is catch memory so efficient despite its small size?– The answer is 80-20 rule.– Most computers spend 80 percent of the time

accessing only 20 percent of the data.

Catch memory

INPUT / OUTPUTINPUT / OUTPUT

• Non-storage devices – Keyboard and monitor– Printer

• Storage devices– Magnetic storage devices– Optical storage devices

Input/Output devices

Physical layout of a magnetic disk

• CD-ROM: compact disc ROM– Capacity: 650MB

• CD-R: compact disc recordable• CD-RW: compact disc rewritable• DVD: digital versatile disc– Capacity: 4.7GB – 17GB

Optical storage devices

SUBSYSTEMINTERCONNECTION

SUBSYSTEMINTERCONNECTION

Connecting CPU and memory using three buses

• Data bus:– The number of wires depends on the size of

the word• Address bus:– The number of wires depends on the address

space of memory• Control bus:– The number of wires depends on the total

number of control commands a computer needs

Buses

Connecting I/O devices to the buses