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.

Registers and their role Processing speed 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. digital logic circuits in the ALU are built up of gates - these gates are specific electronic circuits that produce an output signal that depends upon their input. e.g the OR logic gate if either a or b inputs are positive, then the output will be positive. with the AND gate, both a and b must be positive for the output to be positive Refer to Stallings, electrical engineering Control unit : sends signals to the ALU, registers and buses to direct their operation. Uses the system clock to keep time, coordinate functions. Generates signals to move data between registers, increment the program counter etc.

Four Box Diagram Input Output 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) A register may have a specific purpose or it may be general purpose. The number and type of registers varies from cpu to cpu. clock - clock ticks for each step within the cycle

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)

CPU How the components interact ALU Control Unit Primary Memory Secondary Memory i.e. hard drive CD R/W Floppy ALU Registers Control Unit Primary Memory CPU exchanges data with memory via the registers such as IR and PC.