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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.
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Question 2. Components of a Computer system?
A computer system comprises of the following components: 1.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 functions
and co_ordinate all hardware 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:
Main memory
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contains the current instruction to be executed.
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.
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• General Purpose Register:
for general purpose procedures.
Please refer to diagram for an illustratin of the basic components of the CPU.
CPU I
N T E R N A
L to main
Control unit
Arithmetic Logic Unit
Accumulator
Program Couter
B
U memory
S
Instruction Register
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. 2.Input units
- Used to enter data( raw unprocessed facts) and instructions to the computer.
3.Output units
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- Used for delevering the processed result from the computer in useful form.
4.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
A3 A2 A1
A3
A2 A1
Virtual Memory
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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 response
- Dis:
efficiency is more important than time.
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 directly as soon as it is being transacted. There information will be processed immediately and updated into the master file.
- Ads:
Enter availability of information for decision making.
More accurate data capture. Schedules suits user.
- Dis:
CPU time is used less efficiently.
Random arrival of operator process separately.
transactions, terminal each transaction
More expensive than batch processing. Question 3. Real Time Processing System?
- Def: One which controls the environment by receiving data processing them and returning results sufficiently quickly to affect the functioning of the environment at that time.
- Ads:
Response time is very critical and sufficient quick.
- Dis:
Expensive hardware & software.
Very complex in terms of hardware & software.
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