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Components of a computer system
Hardware
 Central Processing Unit (CPU)
 Memory
 Input and Output Devices
Software
Data
Systems
Higher Computing
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.
Systems
Higher Computing
Basic concepts - Hardware
• CPU performs actual processing of data.
• Data and programs are stored in memory,
and moved to and from CPU as required.
•
Systems
Data travels between system components
along electronic pathways, (sets of wires),
called buses.
Higher Computing
We will look at:
 Four Box diagram
 CPU
 Memory
 Registers and their role
 Processing speed
Systems
Higher Computing

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

Systems
Control unit fetches and interprets
instructions in memory and generates signals
to control all other system components.
Higher Computing
Four Box Diagram
CPU
Input
Processor
Memory
(RAM and ROM)
Output
Backing
Store
Systems
Higher Computing
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.
Systems
Higher Computing
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
Systems
Higher Computing

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)
Systems
Higher Computing
Semiconductor main memory
Primary memory is made up of RAM and ROM
Types include:
 RAM (Random Access Memory)
 ROM (Read Only Memory)
Systems
Higher Computing
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)
Systems
Higher Computing
How the components interact
CPU
Secondary
Memory
i.e. hard drive
CD R/W
Floppy
Primary
Memory
Registers
ALU
Control
Unit
– CPU exchanges data with memory via
the registers such as IR and PC.
Systems
Higher Computing