What is a computer ?

A computer is an electronic device that can accept data and instruction, process them or store them for later retrieval, and sometimes generate output.

Major functions of Systems.

Input Processing Output

Storage

Categories of Computer hardware

1.The central Processing Unit (CPU)2.Input devices, Which allow data to be

entered into the computer 3.Output devices, which are use for

outputting data from the computer . 4.Storage devices both primary and

secondary.

Central Processing Unit (CPU) It is the part of the computer that

does the processing. It also controls the transfer of data between memory and the other devices.

Main Components of the CPU are: 1. The control Unit (CU)2. The Arithmetic/Logic Unit

The Control Unit (CU)

The CU is the part of the CPU which control the operation of the CPU. It is use to:

1.To control the flow of programs and data in and out of the primary memory.

2.To read and interpret program instructions

3.To control the flow of information to and from all the components of the computer.

The Arithmetic/Logic Unit This is the part of the CPU that does

the following: 1.Performs arithmetic operations.

These operation include addition, subtraction etc.

2.Perform logical operations. These includes reasoning and performing the comparisons necessary to make decisions.

Primary Storage

Primary storage is the storage that is directly available to the CPU. It is also known as:

Main Memory Direct Access Storage Immediate Access Storage (IAS)

Primary Storage is made up of 2 types of storage RAM and ROM.

Primary Storage

RAM ROM

What is Random Access Memory (RAM)

The contents in this type of memory are temporary and are lost when the computer is turn off (the data is volatile).

RAM is use to store the instruction and data for currently running program and the operating system.

Types of RAM

Static RAM (SRAM)

Dynamic Random Access Memory (DRAM)

Synchronous DRAM (SDRAM)

What is READ ONLY MEMORY(ROM)This is a chip or a group of chips

containing instructions for the CPU. Only the CPU has access to this memory type.

When we turn on the computer, the CPU gets its first instructions from the ROM.

Types of ROM

Programmable Read only Memory (PROM)

Erasable Programmable Read Only Memory (EPROM).

Electrically Erasable Programmable Read Only Memory (EEPROM).

Comparison Between ROM and RAM

RAM ROM

Data can be both read and written

Read-Only

Volatile Non-volatile

Content modify by program on the computer in question

Content modify by manufacturer

Use Chips

Data can be randomly access

Secondary Storage Unlike primary storage, secondary

storage is not done on chips. Some examples of secondary storage devices are:

1.Hard disks 2.Magnetic tape3.Floppy disk 4.Microfilm5.Optical disk 6.Flash drive/flash memory card

Technical terms used with the storage of data 1. Bit – it is the smallest unit of storage 2. Byte- is a group of eight bits 3. Word – the size of the data or

instruction that the CPU can handle in a single cycle.

4. Word- length /word size – the number of bits in a word

5. Address – the location in memory where data is stored

6. Character – any digit, letter or symbol

Input/output Devices

Input Devices1.Mouse 2.Keyboard 3.Joystick 4.Scanner 5.Microphone

Output Devices 1.Monitor 2.Printer 3.Plotter 4.Speakers

Questions 1. Name three devices other than the typical

computer where ROM may be use. 2. You were typing a document on the

computer and the power to the computer was interrupted momentary. When the computer was restarted the document was no longer in memory. a. explain why the document was not still in memoryb. Give on precaution that can be employed to ensure that a document is not completely lost in the event of a power failure.

Home Work

Explain what is a Bistable device ?