The Central Processing Unit

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CHAPTER 4

• The Central Processing Unit

2
Chapter Overview

• Microprocessors
• Replacing and Upgrading a CPU

3
Microprocessor Basics

• Components
• How microprocessors work
• PC microprocessor developments and features

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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 current width of
conductors.
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The CPU

• Performs operations , decodes and executes
  instructions
• Controls computer operation
• Includes transistors, integrated circuits, and
  microprocessors

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Note P4 775 pins
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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) unit
• Fetches data from the outside and passes data
  back to the external bus

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• 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 (8 clock
  cycles).

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REGISTERS
Control unit components
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Memory
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How Microprocessors Work
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Adding Two Simple

• 2 2 involves more steps than a 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

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PC Microprocessor Developments and Features

• Use the following elements to measure CPU
  performance
• Speed max no. of clock cycles measured in MHz
• Higher the speed, quicker a command will be
  executed
• Transistors More switches means more power
• Registers Larger the register size, more
  complicated command can be processed
• External data bus if large , more and complex
  can be executed
• Address bus determines the max amount of memory
  that can be addressed by CPU
• Internal cache It is high speed Memory built
  into the processor. It is the place to store the
  most frequently used data instead of sending it
  to the slow speed devices ( HDD , RAM)

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Virtual Memory

• Is the art of using Hard disk space to hold the
  data not immediately required by processor

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Possible Upgrade Scenarios

• 8086/8088
• 8028680486
• 80386SX
• Pentium I
• Pentium II
• Pentium III

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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 result
• Combining all above steps in a single step is
  called Pipelining

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Pipelining types

• Superscalar technology allows the Pentium to have
  two instruction Pipelinescalled U and V.
• U Pipeline can execute the full range of Pentium
  instructions
• V 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
  simultaneously-known as Multithreading

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Inserting a CPU

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

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Chapter Summary

• Understanding processor development and progress
  is essential.
• The three key elements for measuring a CPUs
  performance are its speed, address bus, and
  external data bus.
• Several key CPU developments have occurred since
  the 80286 processor.
• Todays 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.

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Assignment

• Presentation slides About CPU history from page
  53 to 66.
• Last day Monday 14th , April