THE CPU

Contents

Introduction to the CPU Main Operations of the CPU

Explanation of Operations Main components of the CPU What determines a CPU’s performance, w

hat to look for, for a fast CPU. CPU Comparison table CPU Comparison chart

Mr. Clarkson Talks About... The CPU (for GCSE Computing)

Introduction to the CPU

The CPU is the portion of the computer system that carries out instructions of a computer program, to perform the basic arithmetical, logical, and input and output operations of the system. It acts as the BRAIN OF THE COMPUTER

Operations

The fundamental operation of most CPUs, regardless of the physical form they take, is to execute a sequence of stored instructions called a program. The instructions are kept in some kind of computer memory. There are three steps that nearly all CPUs use in their operation: fetch, decode, and execute

The three steps Fetch- Gets next program instruction from the

computer’s memory Decode- Figure out what the program is telling

the computer to do Execute- Perform the requested action Write-back (Store)- Write (store) the results to a

register or to memory

Main Components of the CPU

The ALUMicroprocessor:.

Registers- Stores the most frequently used instructions and data

Arithmetic-Logic unit- Performs arithmetic or logical operations

Accepts digital data as input, processes it according to instructions stored in its memory, and provides results as output.

What determines a CPUs performance?• Data bus width- The number of pathways

within the CPU that transfers data (8, 16, 32, 64)

• Word size- The maximum number of bits of data that the CPU can process at a time (8 bits, 16 bits, 32 bits, 64 bits)

• Operations per cycle (clock speed)- The number of clock cycles per second measured in Megahertz (MHz) or Gigahertz (GHz)

Specifications:

Clock Speed: 1.0 GHz

System / Front Side Bus Speed: 133 MHz

Level 1 Cache: 16K Instruction + 16K data

Level 2 Cache: 256 KB

CPU Comparison table

CPU GenerationProcess Number

Data/Address

GP Register Memory Internal

Technology transistorsBus width

(bits)width (bits) Bus speed Clock speed

Intel 8080 1st 6.0 microns 6 000 8 /16 82 MHz 2 MHz

Intel 8088 1st 3.0 microns 29 000 8 / 16 164.77-8 MHz 4.77-8 MHz

Intel 8086 1st 3.0 microns 29 000 16 / 20 164.77-8 MHz 4.77-8 MHz

Intel 80286 2nd 1.5 microns 134 000 16 / 24 166-20 MHz 6-20 MHz

Intel 80388 DX

3rd1.5 / 1.0 microns

275 000 32 / 32 3216-33 MHz 16-33 MHz

Intel 80386 SX

3rd1.5 / 1.0 microns

275 000 16 / 32 3216-33 MHz 16-33 MHz

Intel 80486 DX

4th 1.0 microns 1.2 million 32 / 32 3225-50 MHz 25-50 MHz

Intel 80486 DX2

4th 0.8 microns 1.2 million 32 / 32 3225-40 MHz 50-80 MHz

AMD 5x86 4th0.35 microns

1.2 million 32 / 32 3233 MHz 133 MHz

Intel Pentium 5th

0.8-0.0.35 microns

3.1 million 64 / 32 3260-66 MHz 60-200 MHz(P5/P54C)

Cyrix 6x86 (M1)

5th 0.6 microns 3.0 million 64 / 32 3250-75 MHz100-150 MHz(P120-200)

CPU Comparison chart

Inte

l 8080

Inte

l 8088

Inte

l 8086

Inte

l 80286

Inte

l 80388 D

X

Inte

l 80386 S

X

Inte

l 80486 D

X

Inte

l 80486 D

X2

AM

D 5

x86

Inte

l Penti

um

Cyri

x 6

x86 (

M1)0

50

100

150

200

250

CPU

Inte

rnal C

lock s

peed

(M

Hz)

Mr. Clarkson Talks About... The CPU (for GCSE Computing)