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Computer system


















Computer System

Book I: computer system fundamentals.
Chapter 1: INTRODUCTION TO COMPUTER.
Question 1. What is a computer?
A computer may be defined as a machine which accepts data from an input device, processes it by performing arithmetical and logic operations in accordance with a program of instructions and returns the results through an output unit.
A computer is basically an electronic machine operating on current.
Question 2. Components of a Computer system?
A computer system comprises of the following components:
Central Processing Unit (CPU).
CPU is the heart of the whole sys
CPU consists of the :
control unit (CU)
arithmetic logic unit (ALU)
accumulator (ACC)
program counter (PC)
instruction register (IR)
memory address register (MAR)
memory data register (MDR)
status register (SR)
general purpose register
The function of each components of CPU:
Control unit:
control and co_ordinate all hardware functions of the CS.
examine and decode all program instructions to the computer and initiate their execution by sending the appropriate signals.
ALU:
performs all arithmetic and logic comparision two values functions required by computer.
ACC:
holds the first operand of the temporary result of the ALU.
PC:
contains the add of the next instruction to be excuted.
IR:
contains the current instruction to be executed.
Main memory
MAR:
holds the address location to or from which data is to be transferred
MDR:
contains the data to be written to or read out of the addressed location.
SR:
keeps track of the status of the accumalator.
General Purpose Register:
for general purpose procedures.
Please refer to diagram for an illustratin of the basic components of the CPU.

CPU

Control unit
Arithmetic Logic Unit
Accumulator
Program Couter to main
Instruction Register memory
Memory Address Register
Memory Data Register
Status Register
General Purpose Register


Basic components of a CPU.




Control Unit

Input Unit ALU Output Unit

Main Memory



Backing Storage


Control signals
Data flow
Components of a CS.
Input units
Used to enter data( raw unprocessed facts) and instructions to the computer.
Output units
Used for delevering the processed result from the computer in useful form.
Backing storage units
Backing storage units need for high capacity data storage devices that can store data in a more permanent form for later retrieral, updating and referencing.
Backing storage is also called secondary storage external storage and auxiliary storage.
Chapter 2: MICOPROCESSOR.
Question 1. Cache Memory?
Cache memory is a small amount of very fast store with faster access time than the main memory.
Cache memory is used to temporaryty store data instructions that are likely to be retrieved many times, thus speeds up the processing of data.
Sits between main storage and the processor acting as holding area through which all data and instructions pass.
Old data in the cache memory is over written by new then cache is full.
Question 2. Virtual Memory?
Virtual memory makes use of both the main memory and backing store.
In a virtual memory sys, each user has the illusion that his program is in the main memory all the time.
The sys maintains this illusion by keeping some of the “unused” portion of the program’s code and data on a backing store device which is usually magnetic disk
The movement of the unused portion from the backing store to the mian memory is transparent to the users.
Please refer to diagram for virtual memory.

Backing Store Main Memory




























Virtual Memory

Chapter 3: BATCH/ ONLINE AND REAL TIME PROCESSING SYSTEM.
Question 1. Batch Processing System?
Def: Computer processing does not begin until all the input data has been collected and grouped together called Batched Generally data is accumulated for a certain period of time or unitl a certain quantity.
Ads:
Response time is not critical.
Need to process large volumn of data.
Computer efficiency is more important than response time.
Dis:
Time between recording and processing of source document is long
Rereen normally required if errors are encountered.
Data is not current.
Error correction is more difficult.
Question 2. Online Processing System?
Def: Inputs data enters the computer