CHAPTER 4

The Central Processing Unit

Chapter Overview

Microprocessors Replacing and Upgrading a CPU

Microprocessor Basics

Components How microprocessors work PC microprocessor developments and

features

The External Data Bus- Information is transmitted through a computer using binary code traveling through a bus.- 8 bit data bus: allowed for the transfer of 1 byte of information at a time.- The width of the external data bus increaed to 16, and the 32 32 current width of conductors. (HW3) is that correct?current width of conductors. (HW3) is that correct?

The CPU Performs operations , decodes and

executes instructions Controls computer operation Includes transistors, integrated circuits,

and microprocessors

Note: P4 contains 775 pins

HW3: P5 Contains …… Pins

Microprocessor Design

Three subsystems Control unit (CU):The control unit of the CPU contains circuitry that uses electrical signals to

direct the entire computer system to carry out, or execute, stored program instructions .

Arithmetic logic unit (ALU):The arithmetic/logic unit (ALU) contains the electronic circuitry that executes

all arithmetic and logical operations.

Input/output (I/O) unitFetches data from the outside and passes data back to the external bus

Registers: Are temporary memory storage areas used during data manipulation.

- Codes ( ASCII) Clock :• Timing allows the electronic devices in the computer to coordinate

and execute all internal commands in the proper order.• Pulse of voltage is called clock cycle.• Every computer command needs at least 2 clock cycles.

Clock speed • The clock rate suggests how many commands can be completed in

two cycles.• Adding two numbers would take 4 commands (__?__ clock cycles).

REGISTERS

Program counter (PC): Contains the address of an instruction to be fetched.

Instruction register (IR): Contains the instruction most recently fetched.

Memory address registers (MAR): Contains the address of a location in memory.

Memory buffer register (MBR): Contains a word of data lo be written to memory or the word most recently read.

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Control unit components

PSW ( take home class test)

Memory

How Microprocessors Work

Adding Two Simple

2 + 2 involves more steps than a 2 + 2 involves more steps than a man :man :

A = 2 Translated into binary and routed to CU and sent to X location of memory

When we press + , it is translated into binary and alerts ALU to be ready for addition

B= 2 is translated into binary again ALU sums A and B ALU sends the code for 4 to be stored in an

address register Pressing = key is the last user action BUT the = is

also translated into machine language Sum is computed

PC Microprocessor Developments and Features Use the following elements to measure CPU

performance: Speed : max no. of clock cycles measured in MHzmax no. of clock cycles measured in MHz

Higher the speed, quicker a command will be executedHigher the speed, quicker a command will be executed Transistors: More switches means more powerMore switches means more power Registers: Larger the register size, more complicated Larger the register size, more complicated

command can be processedcommand can be processed External data bus: if large , more and complex can be if large , more and complex can be

executedexecuted Address bus: determines the max amount of memory that determines the max amount of memory that

can be addressed by CPUcan be addressed by CPU Internal cache It is high speed Memory built into the It is high speed Memory built into the

processor. It is the place to store the most frequently used data processor. It is the place to store the most frequently used data instead of sending it to the slow speed devices ( HDD , RAM)instead of sending it to the slow speed devices ( HDD , RAM)

Virtual Memory Is the art of using Hard disk space to

hold the data not immediately required by processor

Possible Upgrade Scenarios

8086/8088 80286–80486 80386SX Pentium I Pentium II Pentium III

Superscalar Technology Main components of processor –registers,

decoders, and ALU are called Instruction Pipeline

To carryout a single instruction, a processor must:* Read instruction * Decode instruction* Fetch (for math function) * Execute* Write back the resultCombining all above steps in a single step is called

PipeliningPipelining

Pipelining types

Superscalar technology allows the Pentium to have two instruction Pipelines–called U and V.

U PipelineU Pipeline can execute the full range of Pentium instructions

V PipelineV Pipeline can execute a limited number Pentium processor breaks a program into

small tasks that are shared b/w pipelines , allowing Pentium to execute two simple Instructions at the same time-known as MultithreadingMultithreading

Inserting a CPU

1. Low-insertion-force (LIF)2. Zero-insertion-force (ZIF)3. Single-edge connector (SEC/slot 1)

Chapter Summary Understanding processor development and

progress is essential. The three key elements for measuring a CPU’s

performance are its speed, address bus, and external data bus.

Several key CPU developments have occurred since the 80286 processor.

Today’s standard processor is the Pentium III chip.

Replacing a CPU is usually simple. You must watch for electrostatic discharge (ESD)

and pin damage when handling a CPU.