A-level Computing 2009/AQA/Advanced Systems Development/Hardware Devices
1.1 Computer Hardware 1.1.1 Computer Concepts A very basic model of a computer would be:
The refined diagram shows the basic components of a computer system.
RAM Random Access Memeory. Stores loaded programs and data to be processed. There are two types: volatile and non-volatile. Unlike non-volatile memory, volatile memory is lost when the computer is switched off or reset.
ROM Read Only Memory. Stores information about BIOS and startup routines.
1.1.2 Measuring Storage Both the primary and auxiliary devices have capacity measured in bits, bytes, kilobytes, megabytes and gigabytes.
A 1 or a 0 is a BInary digiT (Bit).
There are 8 bits in a byte 1024 bytes in a kilobyte 1024 kilobytes in a megabyte 1024 megabytes in a gigabyte Therefore there are 1,048,576 bytes in a megabyte.
A double density floppy disk holds 720Kb of data. A high density floppy disk contains about 1.44Mb of data.
Many computers store one character as one byte.
1.1.3 Computer Categories System Description Microcomputers: This a computer which uses a microprocessor as its CPU. Includes PCs, laptops etc. They typically have between 1 and 128Mb of memory (RAM). They process data in anything from 8-bit ro 64-bit chunks. Minicomputers: These are systems designed for multi-user access several terminals. Varies from processing power from a very powerful micro to a small mainframe. Mainframes: Supports hundreds of terminals for multi-user access. Large amount of primary and auxiliray storage. Supercomputers: These are the fastest and most expensive systems. Although they are not multi-user machines, they are used when a vast amount of processing is to be done.
1.1.4 Computer Configuration This term describes the collection of hardware in use. A large computer configuration would consist of several hundred micros in a building linked together by cabling to form a local area network (LAN).
1.1.5 Embedded Systems An embedded system is dedicated to one specific task. They are special purpose systems.
Embedded systems typically have their programs stored in ROM as opposed to auxiliary storage and RAM. These programs are referred to as firmware - a combination of software and hardware.