Components of a computer system • Hardware • Central Processing Unit (CPU) • Memory • Input and Output Devices • Software • Data
Components of a computer system • Computer hardware provides the physical mechanisms to store, manipulate and input /output data. • Software provides instructions to tell the hardware what tasks to perform • 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.
Basic concepts - Hardware • CPU performs actual processing of data. • Data and programs are stored in memory, and moved to and from CPU as required. • Data travels between system components along electronic pathways, (sets of wires), called buses.
We will look at: • Four Box diagram • CPU • Memory • Registers and their role • Processing speed
Three major components of the CPU: ALU, Control unit and Registers. • The Arithmetic Logic Unit (ALU) operates on binary data to perform all arithmetic and logical functions. • + - * / • < > = <> • AND OR NOT • Rotate Shift • Control unit fetches and interprets instructions in memory and generates signals to control all other system components.
Four Box Diagram CPU Processor Memory (RAM and ROM) Input Output Backing Store
Memory • Purpose of memory is data storage. A hierarchy of memory exists . • data required for immediate manipulation by CPU is stored in small areas of fast access memory within CPU called registers. • data required for active program is generally stored in primary memory, commonly called RAM. • data which may be required at later time generally stored in secondary storage e.g. on disk, tape, or CD-Rom.
Memory: characteristics • Capacity : no of bits, bytes or words in module. Addressable unit - 1 word . Word size may be 8, 16, 32 bits ; (1 byte = 8 bits) • Unit of transfer : RAM = 1 word ; Disk = 1 block • access time or speed - time required to read from memory location. Tradeoff between quantity, cost and speed . As speed increases so does cost. • Also know as Primary Storage
Registers: very fast memory internal to CPU providing temporary storage places for data being manipulated. • System clock generates regular pulses to synchronize all system events and determine the speed at which processing can occur. • Basic measure of system performance is clock speed, measured in megahertz (millions of cycles per second)
Semiconductor main memory • Primary memory is made up of RAM and ROM • Types include: • RAM (Random Access Memory) • ROM (Read Only Memory)
ROM- SECONDARY STORAGE • Read Only Memory • Permanent non-volatile • Software and data fixed during chip manufacture • Cannot be written to • All computers have some ROM to load the Operating System into RAM (bootstrap loader)
ALU How the componentsinteract CPU Secondary Memory i.e. hard drive CD R/W Floppy Registers Control Unit Primary Memory • CPU exchanges data with memory via • the registers such as IR and PC.