Computer Systems

Basic Components

AuxiliaryStorage

OutputProcessor

Main Memory

Input

Types of Input

Keyboard Mouse Barcode readers Scanners Voice data entry OMR OCR

Types of Output

Monitors (also known as VDUs or screens) Printers Plotters Other types ?

The Processor

Processing Power determined by:– Speed of operation of CPU– Amount of memory– Number of I/O devices it can handle

Some control functions of CPU:– Transmission of input data to memory– Process data held in main memory– Transmission of data from main memory to output

devices

Main Memory Made up of individual storage units called bytes Total number of bytes is referred to as computer’s memory size:

= 1,000 bytes (actually 1024)= 1,000,000 (1 million) bytes= 1,000,000,000 (1 billion) bytes= 1,000,000,000,000 (1 trillion) bytes

– 1 Kilobyte (Kb)– 1 Megabyte (Mb)– 1 Gigabyte (Gb)– 1 Terabyte (Tb)

RAM and ROM

RAM – Random Access Memory– Stores current programs and data.– It is VOLATILE – lost when switched off

ROM – Read-Only Memory– Non-VOLATILE.– Instructions or programs permanently etched onto a

chip. For example, bootstrap loader.

Auxiliary Storage Hard disk

– Stores operating system, systems and application software, and data.

– Typical sizes are now 15-20 Gb Floppy disks

– Typical HD disk has capacity of 1.44 Mb. CDs

– Typical capacity of 650-800 Mb. Zip Disks

– Capacity 100 and 250Mb disks. Internal or External models available.