The variety Of Processors And Computational Engines

CS – 355 Chapter- 4

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Introduction

• Processor: It is a digital device which performs computation involving multiple steps.

• Processors can be categorized into groups depending on their functionality and intended use.

Von Neumann Architecture

• System organized in this architecture uses stored program approach.

• Programs and data reside in memory.

• Principle components: processor, memory, I/O devices

From Essentials of Computer Architecture by Douglas E. Comer. ISBN 0131491792. © 2005 Pearson Education, Inc. All rights reserved.

What is a Processor?

• Is Processor = Central Processing Unit

• Processor =

- Device that can perform computation involving multiple steps

- Computes Boolean arithmetic etc

- Need not be expensive and powerful.

Range Of Processors

• Processor categories based on flexibility(least to most)

- Fixed logic

(least flexible, single built operation)

- Selectable logic

(Several functions

Exact function is determined when invoked).

Range Of Processors

- Parameterized logic

• Computes a predetermined function, but input parameters

Programmable Logic

• Most flexible

• Processor given a program to run , typically placed in memory.

Computational engines

• Computer architects use a hierarchical approach to develop the CPU.

• Subcomponents which implement complex functions are designed and tested independently.

• They behave like less powerful processors.

• These are called computational engines.

From Essentials of Computer Architecture by Douglas E. Comer. ISBN 0131491792. © 2005 Pearson Education, Inc. All rights reserved.

CPU with many engines

From Essentials of Computer Architecture by Douglas E. Comer. ISBN 0131491792. © 2005 Pearson Education, Inc. All rights reserved.

Processor categories and Roles

• Coprocessor: under the control of a powerful processor, single task at high speed. Ex: floating point processors, fixed or selectable logic processors

• Microcontroller: programmable device dedicated to the control of physical system. It does not perform any computation as such but tests sensors and sends signals to the control devices.

Ex: door sensors, engine in automobiles

• Micro sequencer: for internal control, controls co-processors and engines with large processors. ex: Micro sequencer to control data movement

• Embedded system processor: they are used to run DVD, Television ,Dial up modems etc.

• General purpose processor: CPU in a PC is an example .

From Essentials of Computer Architecture by Douglas E. Comer. ISBN 0131491792. © 2005 Pearson Education, Inc. All rights reserved.

Processor Technology

• Earlier the processors were made by connecting digital logic circuits together on a circuit board.

• Today the general purpose processor consists of a single integrated circuit.

Stored programs• Most processors follow the Neumann.

architecture.• This is also known as the “stored memory

computer”.• The computer stores the data and programs

instructions in the RAM.• A stored-program machine can easily change the

program, and can do so under program control .• But for other processors like microcontroller

programs cannot be modified.|

Stored Programs

• Processors perform a series of computations

• Programs are stored either

- internally in few cases

- External access location E.g. main memory(easily modifiable)

- ROM

The Fetch-Execute Cycle

• How does the processor identify the next step in the program?

• What are the operations that can be performed and how does the processor perform them?

The Fetch-Execute Paradigm

- Programmable processor accesses 1 step of a stored program executes it and then repeats above with the next step.

The Fetch-Execute Cycle

At some level a programmable processor implements a fetch execute cycle.

The control unit implements the Fetch-decode cycle.

The algorithm used in fetch execute cycle

Repeat forever { fetch: access the next step of the program

from the location in which the program is stored. execute: perform the step of the

program. }

Clock and Instruction rate

• How fast does a fetch execute cycle operate?

• Depends on

-processor(clock speed)

-time to execute each instruction

-Program storage technology

Clock and Instruction rate

• The performance of a processor depends on the speed of the clock.

• Clock rate is not the rate at which the fetch-decode cycle proceeds.

• The execute phase depends on the type of instructions.

• Ex: floating point values requires more clock cycles then integer operations.

Control: of the fetch –execute cycleWorking of the cycleStopping• A processor can be halted permanently by powering

down the computer.• In dedicated systems same program executes

repeatedly.• In general purpose systems the operating system is

running when no application is running.Starting• Processor begins execution from a fixed location.• Possibilities: Reset, Bootstrap loader, soft power

switch

Key Points

• Processors can use fixed or programmable logic.

• Coprocessors, micro sequencers, microcontrollers, embedded processors, general purpose processors.

• All programmable processors follow fetch-execute cycle.