Introduction to microprocessors

INTRODUCTION TO

MICROPROCESSORS

Compiled by: Seble N.

What is Microprocessor?

Intel coined the term in 1971

usually made of millions of microscopic array of electronic

circuits and electronic components (resistors, capacitors,

inductors…) are diffused or implanted to surface of small

silicon chip

its basic function is to take input, process it and then provide

appropriate output

Examples

Pentium, AMD , a PowerPC, a Sun-SPARC or any of the many

other brands and types of microprocessors

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Function of microprocessors

A microprocessor performs three basic steps:

First, it fetches an instruction from memory,

Second, it uses decoding circuitry to determine what the

instruction means (i.e., identify the operations and the

devices involved in it) and

Third, it executes the instruction

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Components of microprocessor

ALU (Arithmetic/Logic Unit)

performs all arithmetic and logic operations

Control Unit

holds the circuitry that controls the process of executing, decoding

and fetching program instructions

it controls the flow of data between the μ-processor and memory

& peripherals

it controls the operation of ALU, I/O devices, and memory unit

Registers

A register is a very small & very fast memory that is built into the

CPU in order to store the current data and instructions which are

being executed by the CPU

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Modes of Processing

Real Mode

One program at a time

Protected Mode

Can run more than one program concurrently and protect them

from each other

Virtual Mode

The processor can swap portion of the memory to the hard disk;

in this way programs running concurrently will have more space

to operate

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Characteristics of microprocessors

Instruction set

the set of instructions that a microprocessor can understand

or execute

Word length

refers to the number of bits a processor can process at a

time

Eg. a 4-bit processor means the ALU can perform a 4-bit data

operation at a time

the longer the word length is the more powerful the

processor is and can process data at a faster speed as

compared to processor with shorter word length

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Characteristics of microprocessors

Speed

measured in HZ = 1cycle/second

Some processors may complete a single instruction per

cycle, or may take one or more cycles

a 2 GHZ CPU may compute 2 billion instructions per second,

if it is able to complete a single instruction in a single cycle

but if it takes 2 cycles to complete a single instruction then it

is only able to compute 1 billion instructions per second

Cache Size

The size of the cache memory

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Characteristics of microprocessors …

Size of registers

refers to the number of bits a microprocessor’s register can

hold at a time

the size of addressable memory is often determined by the

width of registers

Data bus width

Refers to the number of bits a data bus can carry at a time

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Classes of microprocessors

Complex instruction set computer (CISC)

Reduced instruction set computer (RISC)

Application Specific Integrated Circuit (ASIC)

Digital Signal Multiprocessors (DSP)

Superscalar Microprocessors

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Classes of microprocessors …

Complex instruction set computer (CISC)

is more complex and has the ability to perform

complex commands

it allows the user to apply 1 instruction as an

alternative to many simple instructions

can perform complex functions with one instruction

Ex: Intel’s Pentium and Atom chips

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Classes of microprocessors …

Reduced instruction set computer (RISC)

are made according to the function in which the

microprocessor can carry out small things in specific

command

In this way these processors completes more commands

at a faster rate

is simpler, smaller and faster

usually need multiple instructions

Ex: PowerPC and ARM's Cortex chips

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Evolution of Microprocessors

Computing technologies based on vacuum tubes and transistors

In 1959, Fair child semiconductors invented the first integrated circuit

In 1968, Gordan Moore, Robert Noyce & Andrew Grove founded

Intel(Integrated Electronics)

In 1971, the first microprocessor, Intel 4004 was released

In 1972, Intel released the first 8-bit microprocessor Intel 8008

In 1976, MOS technologies introduced the Motorola 6502 an 8-bit

processor, used in Apple I and II

In 1981, the first PC was created by IBM using intel’s 8088 microprocessor

Several companies like Intel, AMD, IBM, ARM, PowerPC, Motorola… make

general purpose processors that are designed for personal computers,

laptops, mobile devices and large central servers

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Evolution of microprocessors

Intel

is generally regarded as the company that sets the

benchmark for others to follow

From the earlier Pentium and Centrino microprocessors to the

Core 2, Core i series

Atom chips for mobiles

The high-end Itanium and Xeon processors for server

applications

Over 90% of laptops use Intel microprocessors

HP, Dell, Apple, Samsung, Sony, Toshiba …

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Top CPU manufacturers

Intel

AMD

Qualcomm

Mediatek

NVIDIA

IBM

Samsung

Motorola

Hewlett-Packard (hp)

Dell

Acer

…

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Intel microprocessors

Intel 4004

Intel 8080

Intel 8085

Intel 8088

Intel 8086

Intel 80286

Intel 80386

Intel 80486

Pentium

Pentium II and III

Dual Core/ Core

Core i3, i5, i7

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Intel microprocessors …

4-bits processors

Intel 4004

1971- the first commercially available

processor as well as the first complete CPU on

a single chip

a 4-bit processor: able to operate on 4 bits of

data at a time

4-bit data bus

had 2,300 transistors

clock speed of 108KHZ

640 bytes addressable memory

was designed for use in calculator but also

used

In traffic light controller, Blood analyzers, and

even in the NASA pioneer 10 deep space probe

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8-bits processors

Intel 8008

first 8-bit microprocessor

200KHz clock speed and 3,500 transistors,

had 6 , 8-bit registers

8-bit data bus

can address up to 16KB

Intel 8080

1974 with 4,500 transistors with up to 2-3MHz

can address up to 64KB

became famous for being used in the Altair 8800 as well as in Boeing's AGM-

86 cruise missile

Intel 8085

was popular as an embedded controller

ran at 5MHZ and contained 6500 transistors

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16-bits processors

Intel 8086

1978, first x86 family microprocessor

16-bit: all registers, internal and external buses

Used 20-bit addressing

Can address 1 million bytes of internal memory

29,000 transistors, 5MHz initially

Intel 8088

was identical to the 8086 with the exception of its 8-bit

internal bus

The IBM 5150, the first IBM PC, came with the 8088

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16-bits processors

Intel 80286

can operate on real and protected mode

134,000 transistors, 6M-8MHz initially

runs faster than the preceding processors

can address up to 16 million bytes of internal memory

was popular in IBM-PC AT and AT PC clones

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32-bits processors

Intel 80386

the first 32-bit microprocessor

32 bit registers & data bus

can operate on protected mode and supports virtual

mode

275,000 transistors

12MHz initially, later 33MHz

Andy Grove decided to single-source producing 386 to

AMD

Later changed in 1991 by AMD AM386

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32-bits processors

Pentium (Pentium I)

32 bit registers

64 bit data bus

Has a high speed cache memory

It can execute more than one instruction per clock cycle

Pentium II and III

Have a dual independent bus that provides separate

path to the system cache and memory

On-die L2 cache

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64-bits processors

New instruction set, not at all related to x86.

Itanium

Released May 29, 2001

733 MHz to 800 MHz

2MB cache

Itanium 2

Released July 2002

900 MHz – 1.6 GHz

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64-bits processors

Intel core 2

x86-64 microprocessor

Two cores on one die

Number of transistors: 291 million

64 KB of L1 cache per core

1.86-3.00 GHz

Intel core i series

Intel core i3, i5, i7

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Intel microprocessors … 25

What is an x86 architecture?

x86 is a family of backward compatible instruction set

architectures based on the Intel 8086 CPU and its Intel

8088 variant

the term "x86" came into being because the names of

several successors to Intel's 8086 processor end in "86",

including the 80186, 80286, 80386 and 80486 processors

all newer processors using Intel's x86 instruction set are still

referred to as x86, i386, or i686 compatible (which means

they all use extensions of the original 8086 instruction set)

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Intel 8086

1978, first x86 family microprocessor

16-bit: all registers, internal and external buses

a CISC processor

can address 1 million bytes of internal memory

used 20-bit addressing

to date backward compatibility has been maintained

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8086 Microprocessor Architecture

The Basic Architecture of the Intel 8086

The processor is partitioned into two logical units

Execution Unit (EU)

Bus Interface Unit(BIU)

Why partition is needed?

Because the processor runs considerably faster than

memory

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Architecture of 8086

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Execution Unit

takes care of the processing including arithmetic and

logic operations

its role is to execute instructions

Contains

ALU,

Control Unit and

Registers

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Bus Interface Unit (BIU)

Its role is to deliver instructions and data to the EU

Function

to manage the bus control unit, segment registers and

instruction queue

to provide access to instructions from memory and place

them in an instruction queue, which varies in size depending

on the processor

This feature enables the BIU to look ahead and prefetch instructions

so that there is always a queue of instructions ready to execute

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Internal Memory of 8086

Memory consists of cells organized in 8-bit

groups

Bytes in memory are numbered consecutively,

beginning with 00

8086

was able to address 1MB of memory

has 20bits wide memory address

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Intel 8086- Memory

RAM

From the 1MB of memory, the first

640K is base RAM

is used for temporary program

storage

ROM

The 8086 Basic Input/Output System

(BIOS) begins at address 768K and

handles

I/O devices, such as a hard disk

controller

ROM beginning at 960K controls the

computer’s basic functions

Power-On Self-Test, dot patterns for

graphics, and the disk self-loader

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Memory Segments

Memory segmentation is the division of computer's

primary memory into segments or sections

Segments are special areas defined in a program for

containing the code, the data, and what is known as the

stack

A segment begins on a paragraph boundary, that is, at

a location evenly divisible by 16, or hex 10.

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Memory Segments …

In real mode, the three main segments are code, data, and

stack

Code Segment:

Contains the machine instructions to be executed

The first executable instruction is at the start of this segment, and the

operating system links to that location to begin program execution

Data Segment:

Contains a program’s defined data, constants, and work areas

Stack Segment:

Contains any data and addresses that the program needs to save

temporarily for use on subroutines

A program may contain one or more segments, which may

vary in size, and can be defined in any sequence

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8086/8088 Registers

The registers are categorized into two sets:

Data registers

are for calculations

Address registers

used to store memory addresses that point to locations in

memory where data will be retrieved or stored

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8086/8088 Data Registers

aka general purpose registers, these are

AX - Accumulator register

BX - Base register

CX - Counter register

DX - Data register

each are 16-bit long and can also be accessed as two 8-bit

registers

AX AH & AL

BX BH & BL

CX CH & CL

DX DH & DL

The 80386 introduced an extended 32-bit general purpose

registers named EAX, EBX, ECX and EDX

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8086/8088 Data Registers

AX register

is used for operations involving input/output and arithmetic

BX register

given the name base register because it is the only general purpose register that can be used as an index in indirect addressing

can also be used for computations

CX register

usually used to control the number of times a loop is repeated or a value to shift bits left or right in bit shifting operations

can also be used for computations

DX register

is used for operations involving input/output and most arithmetic

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8086/8088 Address Registers

Segment registers: used to store starting address of memory segments

Code Segment register

Data Segment register

Stack Segment register

Extra Segment register

Index registers: used for indexed addressing and string operations

Source Index register

Destination Index register

Pointer registers: used to store offset address within memory segments

Instruction Pointer register

Stack Pointer register

Base Pointer register

All the above address registers are 16-bit long in 8086/8088

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8086/8088 Segment Registers

CS register: used to hold starting

address of program’s code segment

DS register: used to hold starting

address of program’s data segment

SS register: used to hold starting

address of program’s stack segment

ES register: used to hold starting

address of programmers defined

extra data segment

FS and GS registers: additional

extra segment registers introduced

by the 80386

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8086/8088 Pointer Registers

IP (Instruction Pointer) register

used to locate a specific location within the code segment

used to hold offset address of the next instruction to be

executed

SP (Stack Pointer) register

used to hold offset address of the top of the stack segment

points to the current word being processed in the stack

BP (Base Pointer) register

used to point to a specific location in the stack

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8086/8088 Index Registers

SI (Source Index) & DI (Destination Index) registers

are used to locate a specific location within the data

segment

both are used in string handling operations. In this

context, SI is associated with the DS register while DI is

associated with the ES register

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Flags Register

Is the status register in Intel x86 microprocessors that shows the current

state of the processor

In 8086 flags register is 16 bits wide, among which 9 are active

They are modified automatically by the processor after instruction

execution, which allows to determine the type of the result and also

conditions to transfer control to other parts of the program

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Flags Register …

The flags bits has two groups

Status flags: reflect the result of an operation executed

by the processor

SF, ZF, AF, CF, PF & OF

Control flags: enable or disable certain operations of

the processor

Trap flag (TF)

Interrupt flag (IF)

Direction flag (DF)

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Flags Register: control flags

The Trap Flag

Permits operation of the processor in single-step mode

Setting TF (TF=1) puts the processor into single step mode for debugging, where the processor automatically generates an internal interrupt after each instruction, allowing a program to be inspected as it executes instruction by instruction

The Interrupt Flag

Indicates that external interrupts, such as keyboard entry, are to be processed or ignored

Clearing IF (IF=0) disables interrupts

The Direction Flag

Determines left or right direction for moving or comparing string (character) data

If DF=1, the string instruction will automatically decrement the pointer

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Flags Register: Status Flags

SF (Sign): Indicates the resulting sign of an arithmetic operation (0 =

positive and 1 = negative)

ZF (Zero): Indicates the result of an arithmetic or comparison

operation (0 = nonzero and 1 = zero result)

PF (Parity): indicates the number of 1-bits that result from an

operation. (0=even parity and 1 = odd parity)

AF (Auxiliary Carry): contains a carry out of bit 3 into bit 4 in an

arithmetic operation

OF (Overflow): indicates overflow of a high-order(leftmost) bit following in a signed arithmetic operation

CF(Carry): contains carries from a high-order bit following an

unsigned arithmetic operation; also contains the contents of the last bit

of a shift or rotate operation

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Introduction to microprocessors

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