Components

Control Processor

• It directs the step-by-step operation of the entire computing system.
• fetches, decodes and executes machine language instructions by prompting ALU or I/O processor

Arithmetic and Logic unit

• ALU does comparisons, addition, subtraction, multiplication and division, fixed and floating point arithmetic when requested by CPU.

Instruction register/decoder

• Part of the CPU which matches a machine language instruction with a set of prestored instructions and when a match is found, processes it.

Instruction pointer/program counter

• A counter that indicates the location of the next computer instruction to be interpreted.

Address Processor

• Processes the CPU's instructions when an address is requested.

I/O Processor

• To input or output data via a device in a suitable form for that device., For example;
  * 1 character at a time for VDU
  * A block of characters at a time for a disk.

I/O (System) Bus

• This interconnects the CPU, memory, and peripherals (eg. Hard Disk) etc with each taking turns at using the bus to transfer data. See separate section for further details.

• Holds data and instructions after input until needed by the CPU
• Inputs are received from Disk, Keyboard, Mouse, other peripherals

Three memory types interact with the CPU

Read only Memory Read Only Memory; memory that has been pre-programmed, and cannot be easily changed Random Access Memory memory that can be easily accessed, and changed Cache Memory High speed RAM working at a speed to match the processor; not usually user-changeable, or controlled. It holds data recently accessed from external storage ready for use Cache RAM

• Measured in MegaHertz.,
• Each instruction is performed in the CPU according to the clock ticks.
• Some instructions may take up to 6 clock ticks or cycles.
• History( Clock speed)

[Rev: 26/7/98] Jun-97 © 1997-98 V/2-Com (Verhaart), P O Box 8415, Havelock North, New Zealand.