Hardware

Nick Sims

        The components of a computer

Types of computer

Microcomputers- desktop, laptop, notebook and palmtop personal computers (PCs)- used in businesses, schools/colleges and homes- cost from a few hundred pounds to a few thousand

http://www.youtube.com/watch?v=RiTb3-t4YJk&feature=related

Computers can be categorised into four types

Types of computer

Minicomputers- often used as multi-user systems, with 100’s of workstations or

terminals attached to a central minicomputer, e.g. EPOS.- cost from £10,000 to about £150,000.

Computers can be categorised into four types

Types of computer

Mainframe computers- used by large organisations which may have 1000’s of terminals,

often remote- cost ££ hundreds of thousands

Computers can be categorised into four types

Types of computer

Supercomputers- largest category of computer used mostly by scientific & industrial research departments, NASA, the Weather Centre, stock exchanges- cost ££ millions

Computers can be categorised into four types

CPU

Controls the transmission of data from input devices to memory

Processes the data held in main memory

Controls the transmission of information from main memory to output devices

Main memory

Instructions and data are held in main memory, which is divided into millions of individually-addressable storage units called bytes.

One byte can hold one character, or it can be used to hold a code representing, for example, a tiny part of a picture, a sound, or part of a computer program instruction.

The total number of bytes in main memory is referred to as the computer’s memory size. Computer memory sizes are measured as follows:

1 Kilobyte (Kb) = 1000 bytes (to be exact, 1024 bytes)1 Megabyte (Mb) = 1,000,000 (1 million) bytes1 Gigabyte (Gb) = 1,000,000,000 (1 billion) bytes1 Terabyte (Tb) = 1,000,000,000,000 (1 trillion) bytes

Random Access Memory (RAM) ‘Ordinary’ memory

Used for storing programs which are currently running and data which is being processed.

This type of memory is volatile - it loses all its contents as soon as the machine is switched off.

RAM

Read Only Memory (ROM)

Non-volatile, with contents permanently etched into the memory chip at the manufacturing stage

Used for example to hold the bootstrap loader, the program which runs as soon as the computer is switched on and instructs it to load the operating system from disk into memory.

ROM

Cache Memory Very fast memory used to improve the speed of a computer, doubling it

in some cases

Acts as an intermediate store between the CPU and main memory

Stores the most frequently or recently used instructions and data for rapid retrieval

Generally between 1Kb and 512Kb

Much more expensive than normal RAM

Auxiliary Storage

Hard disks

- all standalone PCs have in-built hard disk- typical capacity for Desk top computer: 160 GB- used for storing software including the operating system, other systems software, application programs and data

Auxiliary Storage

(Digital Versatile Disc or Digital Video Disc)

DVD-RW

• Media type: Optical disc• Capacity~4.7 GB

(single-sided, single-layer)~8.54 GB (single-sided, double-layer)~9.4 GB (double-sided, single-layer)~17.08 GB (rare—double-sided, double-layer)

Auxiliary Storage

Blu-ray Disc (also known as

Blu-ray or BD) Media type: high-density

optical disc EncodingMPEG-2,

H.264/MPEG-4 AVC, and VC-1

Capacity25 GB (single-layer)and 50 GB (dual-layer)

In the future will hold up to future 1 TB

Its main uses are for storing high-definition video, PlayStation 3 games, and other data, with up to 25 GB per single layered, and 50 GB per dual layered disc.

Auxiliary Storage

USB Flash-Drive Consists of flash

memory data storage device integrated with a USB (Universal Serial Bus) interface

Can have a capacity of 64GB

Auxiliary Storage

Floppy disks

- thin sheet of mylar plastic in hard 3½” casing - capacity 1.44Mb

CD-ROM - holds about 650Mb to 800 MB (some hold 900 MB)

Auxiliary Storage

Zip disks

- hold up to 250Mb

Input and output devices

Input devices- Keyboard- mouse- barcode readers - Scanners

http://www.youtube.com/watch?v=LtKQNwqNLLk

Output devices - printer- plotter- VDU

Can you name some others?

Global Positioning System

Bluetooth