Computer Architecture

Abhinav Agarwal

Veeramani V.

Outline

Introduction of a Microprocessor Microprocessor design objectives and constraints Structure Interface ISA Microprocessor Instructions Number Systems

What is a Microprocessor?

A circuit of transistors and other electrical components on a chip that can process programs, remember information, or perform calculations.

The heart of every CPU Requires programmed input Advantages over a customised digital

circuit Cost Scalable Single design – multiple use

© Intel Corp.

Design objectives

Maximize Performance Speed of operation: How quickly an operation can be completed Throughput: No of operations completed in unit time, not necessarily

the same as speed, consider Servers.

Maximize Productivity Interface provided must be easy

Be one step ahead of market needs and two steps ahead of competition

Dramatic progress over the years

© Intel 4004 Processor

Introduced in 1971

2300 Transistors

108 KHz Clock

© Intel P4 Processor

Introduced in 2000

42,000,000 Transistors

1.5 GHz Clock (Initial)

Design Constraints

Power consumed Today’s processors consume a peak power of 100 W, which means a

peak current of nearly 80A.

Area Cost Backward compatibility

Windows running on Intel P3 Processor should run on Intel P4 too.

Time taken to design the processor should not be very large or else the competitor may get ahead

Other factors like security, scalability, reliability also need to be considered in processor design

Microprocessor Markets

Desktop Processor for desktop computers. Cost, backward compatibility are very

important. Eg: Intel Pentium, AMD Athlon

Servers Processor for applications requiring huge amount of computation, data

handling like web servers, database servers, scientific computation servers. In general, multiple processors are used. Throughput is a very important metric for servers in general. Eg: Google servers, vsnlproxy

Embedded For applications in electronic appliances, robots, cars, mobiles etc.

Power consumption, cost are very important metrics. Eg: Microcontrollers like 8051, PIC, specifically designed processors for cars, mobiles etc.

Structure

The processor is a computing unit which needs to interact with memory for getting instructions as well as data

ProcessorInstruction Memory

Data Memory

Address (PC)

Instruction

Address (reg)

Data (loads)

Data (stores)

Internal Structure of the Processor Control Unit

Fetches instructions from memory, Interprets them, Controls ALU

ALU Does all computations

Register File Stores variables

Data Address

ALU

(Calculator)

Register File

DataControl Unit

Instr

Control Flags

PC

Data Out

Data In

Instr In

Inst Address

r1r2r3r4

Instruction set architecture (ISA) The first step in any processor design would be to decide

on an ISA ISA is the interface provided by the architect to the

external world The instructions supported with their opcode (The binary representation

of instruction mnemonics) The width (number of bits) of data, instruction, data address, instruction

address Other information necessary to the compiler like number of registers in

the register file etc.

Assembly Code

High Level Language (Like C, C++, Java)

void main ()

{

int a = 22;

int b = 42;

int c = a + b;

}

This conversion is done by compiler

Assembly language

mov r1, 22 // Put the value 22 in R1

mov r2, 42 // Put the value 42 in R2

add r3, r1, r2 // Add the values in R1 & R2 and put result

in R3

Destination

Source1

Source2

Types of Instructions

ALU add, sub, mult, or, and, xor Operands may be Register-register, Register-memory, memory-memory Immediate operands (will be discussed later)

MEM load, store Direct addressed: load r1, 1234H Register Addressed: load r1, (r2)

Control jmp, branch Change value of PC to required location

Converting Instructions to binary codes Each instruction is encoded into a binary format and

stored in the instruction memory. The control unit decodes it and gives appropriate signals

to ALU

add r1, r2, r3

000111 00001 00010 00011

6 bit opcode for the add operation is 000111

Assuming that the register file has 32 registers, each register has a 5 bit code, from r1 to r31,

r1 = 00001, r31 = 11111

Thus total length of instruction = 6 + 5*3 = 21 bits

This is an example of fixed length encoding scheme.

Number Systems

Decimal (D)

Binary (B) Hexadecimal (H or X)

Zero 0 0 0

Nine 9 1001 9

Ten 10 1010 A

Eleven 11 1011 B

Twelve 12 1100 C

Thirteen 13 1101 D

Fourteen 14 1110 E

Fifteen (Largest 4 bit no.) 15 1111 F

Forty Two 42 0010 1010 2A

Largest 8 bit no. 255 1111 1111 FF

Largest 16 bit no. 65535 1111 1111 1111 1111 FF FF

References

“How Microprocessors work” http://www.intel.com/education/mpworks/index.htm

http://www-inst.eecs.berkeley.edu/~cs152/fa05/ppt/ lec1-1.ppt Slides 24-28 lec1-2.ppt lec2-1.ppt