1. Chapter 3 Computer Hard ware
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2. A computer performs basically five major operations :
it accepts data or instructions by any way of input,
it stores data,
it can process data as required by the user,
it gives results in the form of output, and
it controls all operations inside a computer
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3. Computer Hardware Refers to the physical components
Not one device but a system of many devices
Major types of components include:
Central Processing Unit
Main memory
Secondary storage devices
Input devices
Output devices

4. Organization of a Computer System
Central
Processing
Unit
Input
Device
Output
Device
Main
Memory
Secondary
Storage

5. The CPU Fetches instructions from main memory
Carries out the operations commanded by the instructions
Each instruction produces some outcome
A program is an entire sequence of instructions
Instructions are stored as binary numbers
Binary number - a sequence of 1’s and 0’s

6. Main Memory Commonly known as random access memory, or just RAM
Holds instructions and data needed for programs that are currently running
RAM is usually a volatile type of memory
Contents of RAM are lost when power is turned off

7. Secondary Storage A nonvolatile storage medium
Contents retained while power is off
Hard disk drives are most common
Records data magnetically on a circular disk
Provides fast access to large amounts of data
Optical devices store data on CD’s as pits
USB flash memory devices
High capacity device plugs into USB port
Portable, reliable, and fits easily in a pocket

8. Input Devices
Any type of device that provides data to a computer from the outside world
For example:
Keyboard
Mouse
Scanner

9. Output Devices
Any type of device that provides data from a computer to the outside world
Examples of output data:
A printed report
An image such as a picture
A sound
Common output devices include:
Monitor (display screen)
Printer

10. CPU Components Two typical components of a CPU are:
The arithmetic logic unit (ALU), which performs arithmetic and logical operations.
The control unit (CU), which extracts instructions from memory and decodes and executes them, calling on the ALU when necessary.
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11. ALU
The actual processing of the data and instruction are performed by Arithmetic Logical Unit
The major operations performed by the ALU are addition, subtraction, multiplication, division, logic and comparison.
Data is transferred to ALU from storage unit when required
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12. Control Unit (CU) The Control Unit acts like the supervisor
It extracts instructions from memory and decodes and executes them, and sends the necessary signals to the ALU to perform the operation needed.
The control unit determines the sequence in which computer programs and instructions are executed.
Processing of programs stored in the main memory, interpretation of the instructions and issuing of signals for other units of the computer to execute them.
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13. MEMORY There are two kinds of computer memory: primary and secondary.
Primary memory is accessible directly by the processing unit.
RAM (Random access memory) is an example of primary memory
As soon as the computer is switched off the contents of RAM is lost.
You can store and retrieve data much faster with primary memory compared to secondary memory
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14. Primary memory is more expensive than secondary memory.
Secondary memory such as floppy disks ,hard magnetic disk, etc., is located inside and outside the computer.
Primary memory is more expensive than secondary memory.
The size of primary memory is less than that of secondary memory.
Primary memory is faster than secondary memory.
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15. Read Only Memory (ROM)
There is another memory in computer, which is called Read Only Memory (ROM).
The storage of program and data in the ROM is permanent.
The ROM stores some standard processing programs supplied by the manufacturers to operate the computer.
The ROM can only be read by the CPU but it cannot be changed.
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16. PROM is another type of primary memory in computer, which is called Programmable Read Only Memory (PROM).
You know that it is not possible to modify or erase programs stored in ROM, but it is possible for you to store your program in PROM chip. Once the programmes are written it cannot be changed and remain intact even if power is switched off.
Programs or instructions written in PROM or ROM cannot be erased or changed.
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17. When the EPROM is in use information can only be read.
EPROM: Erasable Programmable Read Only Memory, which over come the problem of PROM & ROM.
EPROM chip can be programmed time and again by erasing the information stored earlier in it.
When the EPROM is in use information can only be read.
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