Computer Instr Set

8/8/2019 Computer Instr Set

1/13

Computer Instruction Set


2/13

Review Computer architecture

Two architectures Von Neumann Model

ISA

CISC Architecture and majorcharacteristics

RISC Architecture and major

characteristics


3/13

Computer Architecture

Computer architecture is concerned withthe structure and behavior of the computer.

It includes the information, formats, the

instruction set, and techniques foraddressing memory.

The architectural design of a computersystem is concerned with the specifications

of the various functional modules, such asprocessors and memories, and structuringthem together into a computer system.


4/13

Two Architectures

Two basic computer architectures are vonNeumann architecture and Harvardarchitecture.

Von Neumann architecture describes a

general frame work, or structure, that acomputer hardware, programming, anddata should follow.

Example: desktop personal computer

Harvardarchitecture uses physicallyseparate storage and signal path-ways fortheir instructions and data.

Example: Microcontroller and DSP.


5/13

The Von Neumann Machine, 1945

The Von Neumann model consists offive major components:input unit

output unit ALU

memory unit

control unit.Sequential Execution


6/13

Von Neumann Model

A refinement of the Von Neumann model, the system bus model

has a CPU (ALU and control), memory, and an input/output unit.

Communication among components is handled by a shared

pathway called the system bus, which is made up of the data

bus, the address bus, and the control bus.


7/13

Instruction Set Architecture - ISA refers to

the actual programmer-visible machineinterface such as instruction set, registers,

memory organization and exception

handling.

Computer Architecture


8/13

Instruction set

An important aspect of computerarchitecture is the design of the instructionset for the processor.

Many computers have instruction sets thatinclude more than 100-200 instructions.

A computer with a large number ofinstructions is classified as a CISC,

Complex Instruction Set Computer.

A computer with fewer instructions whichcan be executed much faster is classifiedas RISC, Reduced Instruction SetComputer.


9/13

Instruction Set Architecture (ISA)

Complex Instruction Set (CISC) Single instructions for complex tasks (string

search, block move, FFT, etc.)

Usually have variable length instructions

Registers have specialized functions

Reduced Instruction Set (RISC)

Instructions for simple operations only

Usually fixed length instructions

Large orthogonal register sets


10/13

CISC Characteristics The essential goal of a CISC architecture is to

attempt to provide a single machine instruction

for each statement that is written in a high-levellanguage.

This architecture is the incorporation of variable

length instruction formats.

The instructions in a CISC processor provide

direct manipulation of operands residing in

memory.


11/13

Major characteristics-CISC

architecture1. A large number of instructions- typically

from 100 to 250 instructions

2. Instructions performing specialized tasks

are used frequently.

3. A large variety of addressing modes-

typically from 5 to 20 different modes.

4. Variable-length instruction formats.5. Instructions that manipulate operands in

memory.


12/13

RISC Characteristics The concept involves an attempt to reduce

execution time by simplifying the instruction setof the computer.

The small set of instructions consists mostly ofregister-register operations.

All computations are done among the datastored in processor registers.

An important aspect ofRISC instruction format isthat it is easy to decode.

It has the ability to execute one instruction perclock cycle.


13/13

Major characteristics-RISC

processor1. Relatively few instructions

2. Relatively few addressing modes

3. Memory access limited to load and storeinstructions

4. All operations done within the registers of theCPU.

5. Fixed-length, easily decoded instruction format.

6. Single-cycle instruction execution.

7. Hardwired rather than micro programmedcontrol.

Documents

Computer Instr Set