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 device Computer software consists of instructions and data that computer manipulates to perform various data processing tasks Basic Terms related to Digital computer Program : A sequence of instructions for the computer is called a program. Digital computer

Database: The data that are manipulated by the program constitute the database System 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

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 MEMORY

Table :Memory units Unit Unit kilobyte megabyte gigabyte terabyte petabyte exabyte Exact Number of bytes Exact Number of bytes bytes 2 20 bytes 2 30 bytes 2 40 bytes 2 50 bytes 2 60 bytes Approximation Approximation bytes 10 6 bytes 10 9 bytes bytes bytes bytes Main Memory

Main memory Address space: – the total number of uniquely identifiable locations in memory

Memory addresses are defined using unsigned 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 rule. – Most computers spend 80 percent of the time accessing only 20 percent of the data. Catch memory

INPUT / 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

SUBSYSTEMINTERCONNECTIONSUBSYSTEMINTERCONNECTION

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