Block diagram of computer

A Computer is

• A programmable machine. It can execute or run a pre-recorded list of instructions which follow certain rules (a program).

• Modern computers are electronic and digital. The actual machinery -- wires, transistors , and circuits -- is called hardware; the instructions and data are called software.

Block diagram of computer

Components of a Computer System

• Computer hardware provides the physical mechanisms to process, store, and input /output data. Includes CPU, memory, I/O devices

• Software provides instructions to tell the hardware what tasks to perform. It includes system (eg Windows XP) and application (eg Excel) software

Data in the computer may be representing numbers, characters, graphics etc but is always kept in a form that the hardware and software can manipulate.

Hardware – I/O

• Input Devices collect & translate raw data into form useable by computer. e.g keyboard accepts letters and numbers and converts them to a binary code such as Unicode.

• Output devices produce results in useable form for user (or another device). e.g. monitor converts binary codes to characters and images, whilst modem converts digital data to analog form for transmission over telephone lines.

Hardware – I/O Peripherals

1 Input Devices• Mouse• Keyboard

2 Output Devices• Monitor (VDU)• Printer

3 Secondary Storage Devices• Hard Disk• CD / DVD / Floppy

Hardware - memory

• Memory - Purpose of memory is data storage. Two major types of memory :

• Primary memory - to hold data and instructions during processing – eg RAM. Relatively limited capacity and volatile

• Secondary memory - to provide permanent long term storage – eg hard disk. High capacity and non-volatile

Hardware - memory

• Secondary storage consists of non-volatile high-capacity devices to store programs and data not currently required by CPU.

• Hard and floppy disks, and tapes store data as magnetized spots.

• CD’s and DVD’s store data as pits or surface marks detectable by laser light.

Hardware- memory

• Digital computers deal with data in binary form - all data is represented using just two digits - 1 or 0. Letters and other symbols are assigned unique binary codes.

• Primary memory consists of a set of locations defined by sequentially numbered addresses. Each location contains a binary number that can be interpreted as data or an instruction.

Main Memory (RAM)

1. Different from disk storage

2. used to temporarily store Data

3. in modern computers memory is 512 MB.

Central Processing Unit ( CPU)

1. Acting as the brain of the computer’

2. Currently the Intel-Pentium microprocessor is the most common CPU though there are many types

Hardware- the CPU

• CPU performs actual processing of data, according to instructions from programs.

• Data and programs are stored in primary and secondary memory, and moved to and from CPU as required.

• Signals representing data and instructions travel between system components along electronic pathways, called buses. Capacity of bus is critical to system performance.

Hardware - The Processor

• The CPU is a general purpose processor that performs data manipulation and/or transformation functions including computations, comparisons and data movement.

• The CPU consists of 3 main parts:

– ALU - where arithmetic and logical operations performed

– Control Unit - controls data movement and execution of instructions

– Registers - small high speed storage areas

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