CAD/CAM (SUBJECT CODE: 57024)

UNIT-1

INTRODUCTION

Learning Objectives:

Understand the various spheres of manufacturing activity where computers

are used

Differentiate between conventional and computer based manufacturing

system in product cycle

Explain CAD and its application

Explain various types of manufacturing organisations

Explain CAM and its application

COMPUTERS IN INDUSTRIAL MANUFACTURING

The role of computer in manufacturing may be broadly classified into two groups:

1. Computer monitoring and control of the manufacturing process.

2. Manufacturing support applications, which deal essentially with the

preparations for actual manufacturing and post-manufacture operations.

Second category: The types of support that can be envisaged are:

• Computer aided design and drafting,

• Computer aided engineering,

• Computer aided manufacturing,

• Computer aided process planning,

• Computer aided tool design,

• Computer aided NC part programming,

• Computer aided scheduling,

• Computer aided material requirement planning, etc.

OVERVIEW OF CAD/CAM

What is CAD?

CAD if often defined in a variety of ways and includes a large range of

activities. Very broadly it can be said to be the integration of computer

science (or software) techniques in engineering design. At one end when

we talk of modeling, iIt encompasses the following:

Use of computers (hardware & software) for designing products

Numerical method, optimizations etc.

2D/3D drafting

3D modeling for visualization

Modeling curves, surfaces, solids, mechanism, assemblies, etc.

The models thus developed are first visualized on display monitors

using avariety of techniques including wire frame displa, shaded image

display, hidden surface removed display and so on. Once the designer is

satisfied, these models are then used for various types of analysis /

applications. thus, at the other end it includes a number of analysis

activities. These could be:

Stress (or deflection) analysis, i.e. numerical methods meant for

estimating the behaviour of an artifact with respect to these

parameters. It includes tools like the Finite Element Method

(FEM).

Simulation of actual use

Optimization

Other applications like

o CAD/CAM integration

o Process planning

These are activities which normally use models developed using one or

more of the techniques mentioned above. These activities are often

included in other umbrellas like CAM or CAE. A term often used is

CAD to include this broad set of activities. They all use CAD models

and often the kind of application they have to be used ina determines the

kind of amodel to be developed. Hence, in this course I cover them

under the umbrella of CAD. In this course we will strive to give an

overview of modelling techniques followed by some applications,

specifically CAM.

Thus there are three aspects to CAD.

Modeling

Display/ Visualization

Applications

MODELING

Modelling typically includes a set of activities like

Defining objects

Defining relation between objects

Defining properties of objects

Defining the orientations of the objects in suitable co-ordinate

systems

Modification of existing definition (editing).

The figure below explains what a typical CAD model would need to

define, what kind of entities need to be defined and what relationships

exist between them.

At the highest level we have the volume which is defined by (or

"delimited by") a set of surfaces. These surfaces can be either planar or

curved / warped. A planar surface can be bounded by a set of curves. A

curved surface can be seen as a net of curves. These curves are typically

a succession of curve segemnts which define the complete the curve.

The curve segment is defined using a set of end points / control points

which govern the nature of the curve. Thus a relationship is defined

between entities at each level.

Once such a relationship is defined, a geometric model of the artifact is

available. In any design there might be manysuch artifacts. One then has

to define properties of each of these artifacts and define a relationship

between them. The properties and the relationships needed are

dependent on the application the model is to be used for subsequently.

But one common application that all models have to go through is

visualization of the model (s).

COMPUTER AIDED MANUFACTURE (CAM)

Type of Production

1. Mass production - large lots e.g. automobiles

2. Batch production - medium lot sizes e.g. industrial machines,

aircrafts, etc.

3. Job shop production - small lots or one off, e.g. prototypes,

aircrafts,etc.

What are the advantages of using CAM?

• Greater design freedom:

Any changes that are required in design can be incorporated at

any design stage without worrying about any delays, since there would

hardly be any in an integrated CAM environment.

• Increased productivity:

In view of the fact that the total manufacturing activity is

completely organised through the computer, it would be possible to

increase the productivity of the plant.

• Greater operating flexibility:

CAM enhances the flexibility in manufacturing methods and

changing of product lines.

• Shorter lead-time:

Lead times in manufacturing would be greatly reduced.

• Improved reliability:

In view of the better manufacturing methods and controls at the

manufacturing stage, the products thus manufactured as well as of the

manufacturing system would be highly reliable.

• Reduced maintenance:

Since most of the components of a CAM system would include

integrated diagnostics and monitoring facilities, they would require less

maintenance compared to the conventional manufacturing methods.

• Reduced scrap and rework:

Because of the CNC machines used in production, and the part

programs being made by the stored geometry from the design stage, the

scrap level would be reduced to the minimum possible and almost no

rework would be necessary.

• Better management control:

As shown above, since all the information and controlling

functions are attempted with the help of the computer, a better

management control on the manufacturing activity is possible.

Application

Area

Software

Integrated

System

CAD-2D

drafting

CADCAM, AutoCAD, MicroCADM, VersaCAD

Pro/Engineer

Unigraphics

CATIA

CAD-Solid

modeling

Solid Edges, SolidWorks, SolidDesigner,

mechanical Desktop

I-DEAS

I/MES

EUCLID-IS

CAM

BravoNCG, VERICUT, DUCT, Camand,

Mastercam, Powermill

CAE

MSC/NASTRAN,ANSYS, PATRAN, DADS, C-

MOLDS,MOLDFLOW,MOLDEX, designWorks

PRODUCT CYCLE

Let us consider the manufacturing environment of a given product.

How does the product idea originate?

• The market forces determine the need for a product.

• Expertise on the part of the company estimates the likely demand and

probable profitability and decides on the best mode of designing and

manufacturing the desired product.

The details of such a design and the subsequent manufacturing process are depicted

in Fig. 1-2 for the traditional approach and in Fig. 1-3 for computer aided

manufacturing

Computer Aided Design (CAD)

Is a TOOL to aid designer/engineer

Classified under 2 categories:

1. Product Engineering

• Product functions

• Product Specifications

• Conceptual design

• Ergonomics and Aesthetics

• Standards

• Detailed Design

• Prototype development

• Testing

• Simulation

• Analysis

• Strength

• Kinematics, Dynamics

• Heat, Flow

• Design for Manufacture

• Design for Assembly

• Drafting

2. Manufacturing Engineering

• Process planning

• Process sheets

• Route sheets

• Tooling

• Cutting tools

• Jigs and Fixtures

• Dies and Moulds

• Manufacturing Information Generation

• CNC Part programmes

• Robot Programmes

• Inspection (CMM) programmes

• Production Organisation

• Bill of Materials

• Material Requirement Planning

• Production Planning

• Shop Floor Control

• Plant Simulation

• Marketing and Distribution

• Packaging

• Distribution, Marketing

Today’s CAD technology can provide the engineer/designer the necessary

help in the following ways:

1) Computer aided design (CAD) is faster and more accurate than conventional

methods.

2) The various construction facilities available in CAD would make the job of

developing the model and associated drafting a very easy task.

3) In contrast with the traditional drawing methods, under CAD it is possible to

manipulate various dimensions, attributes and distances of the drawing

elements. This quality makes CAD useful for design work.

4) Under CAD you will never have to repeat the design or drawing of any

component. Once a component has been made, it can be copied in all further

works within seconds, including any geometric transformation needed.

5) You can accurately calculate the various geometric properties including

dimensions of various components interactively in CAD, without actually

making their models and profiles.

6) 6. Modification of a model is very easy and would make the designer’s

7) task of improving a given product simple to take care of any future

8) requirements.

9) 7. Use of standard components (part libraries) makes for a very fast

10) model development work. Also a large number of components and

11) sub-assemblies may be stored in part libraries to be reproduced and

12) used later.

13) 8. Several professional CAD packages provide 3D (3 dimensional)

14) visualisation capabilities so that the designers can see the products

15) being designed from several different orientations. This eliminates

16) the need of making models of products for realisation and explaining

17) the concepts to the team.

18) Not only this, several designers can work simultaneously on the

19) same product and can gradually build the product in a modular fashion.

20) This certainly provides the answer to the need of today’s industry and the

21) one emerging on the horizon.

CAD/CAM HARDWARE

Computer System

Mainframe Computer and Graphics Terminals

Powerful

Inconvenient

High cost

Turn-key CAD System

Dedicated computer systems for CAD applications, cons super-

minicomputer and several design work stations.

Following the "central control concept"

Inconvenient and not powerful enough for complex 3D m

Workstations & High-End Personal Computers

Supporting multiple tasks

Supporting network and file-sharing – convenient

Low costs

Present and trend BASIC STRUCTURE OF COMPUTERS

Computer types: -

A computer can be defined as a fast electronic calculating machine that

accepts the (data) digitized input information process it as per the list of internally

stored instructions and produces the resulting information.

List of instructions are called programs & internal storage is called

computer memory.

The different types of computers are

Personal computers: - This is the most common type found in homes,

schools, Business offices etc., It is the most common type of desk top

computers with processing and storage units along with various input and

output devices. Note book computers: - These are compact and portable versions of PC Work stations: - These have high resolution input/output (I/O) graphics

capability, but with same dimensions as that of desktop computer. These are

used in engineering applications of interactive design work. Enterprise systems: - These are used for business data processing in

medium to large corporations that require much more computing power and

storage capacity than work stations. Internet associated with servers have

become a dominant worldwide source of all types of information.

Super computers: - These are used for large scale numerical calculations

required in the applications like weather forecasting etc.,

Functional unit: - A computer consists of five functionally independent main parts input,

memory, arithmetic logic unit (ALU), output and control unit.

Input ALU

I/O Memory Processor

Output Control Unit

Fig a : Functional units of computer

Input device accepts the coded information as source program i.e. high level

language. This is either stored in the memory or immediately used by the processor

to perform the desired operations. The program stored in the memory determines the

processing steps. Basically the computer converts one source program to an object

program. i.e. into machine language.

Finally the results are sent to the outside world through output device. All of

these actions are coordinated by the control unit.

Input unit: - The source program/high level language program/coded information/simply

data is fed to a computer through input devices keyboard is a most common type.

Whenever a key is pressed, one corresponding word or number is translated into its equivalent binary code over a cable & fed either to memory or processor.

Joysticks, trackballs, mouse, scanners etc are other input devices.

Memory unit: - Its function into store programs and data. It is basically to two types

1. Primary memory

2. Secondary memory

1. Primary memory: - Is the one exclusively associated with the processor and

operates at the electronics speeds programs must be stored in this memory while

they are being executed. The memory contains a large number of semiconductors

storage cells. Each capable of storing one bit of information. These are processed in

a group of fixed site called word.

To provide easy access to a word in memory, a distinct address is associated

with each word location. Addresses are numbers that identify memory location.

Number of bits in each word is called word length of the computer. Programs must reside in the memory during execution. Instructions and data can be

written into the memory or read out under the control of processor.

Memory in which any location can be reached in a short and fixed amount

of time after specifying its address is called random-access memory (RAM).

The time required to access one word in called memory access time.

Memory which is only readable by the user and contents of which can’t be altered is

called read only memory (ROM) it contains operating system.

Caches are the small fast RAM units, which are coupled with the processor

and are aften contained on the same IC chip to achieve high performance. Although

primary storage is essential it tends to be expensive.

2 Secondary memory: - Is used where large amounts of data & programs have to

be stored, particularly information that is accessed infrequently. Examples: - Magnetic disks & tapes, optical disks (ie CD-ROM’s), floppies etc.,

Arithmetic logic unit (ALU):- Most of the computer operators are executed in ALU of the processor like

addition, subtraction, division, multiplication, etc. the operands are brought into the ALU from memory and stored in high speed storage elements called register. Then

according to the instructions the operation is performed in the required sequence.

The control and the ALU are may times faster than other devices connected

to a computer system. This enables a single processor to control a number of external devices such as key boards, displays, magnetic and optical disks, sensors

and other mechanical controllers.

Output unit:- These actually are the counterparts of input unit. Its basic function is to send

the processed results to the outside world.

Examples:- Printer, speakers, monitor etc.

Control unit:- It effectively is the nerve center that sends signals to other units and senses

their states. The actual timing signals that govern the transfer of data between input unit, processor, memory and output unit are generated by the control unit.

Basic operational concepts: - To perform a given task an appropriate program consisting of a list of

instructions is stored in the memory. Individual instructions are brought from the

memory into the processor, which executes the specified operations. Data to be

stored are also stored in the memory.

Examples: - Add LOCA, R0

This instruction adds the operand at memory location LOCA, to operand in

register R0 & places the sum into register. This instruction requires the performance of several steps,

1. First the instruction is fetched from the memory into the processor.

2. The operand at LOCA is fetched and added to the contents of R0

3. Finally the resulting sum is stored in the register R0

The preceding add instruction combines a memory access operation with an

ALU Operations. In some other type of computers, these two types of operations are

performed by separate instructions for performance reasons. Load LOCA, R1 Add R1, R0

Transfers between the memory and the processor are started by sending the

address of the memory location to be accessed to the memory unit and issuing the appropriate control signals. The data are then transferred to or from the memory.

MEMORY

MAR MDR

CONTROL

PC R0

R1

…

ALU

…

IR …

…

Rn-1

n- GPRs

Fig b : Connections between the processor and the memory

The fig shows how memory & the processor can be connected. In addition

to the ALU & the control circuitry, the processor contains a number of registers used for several different purposes.

The instruction register (IR):- Holds the instructions that is currently being

executed. Its output is available for the control circuits which generates the timing

signals that control the various processing elements in one execution of instruction.

The program counter PC:-

This is another specialized register that keeps track of execution of a program. It contains the memory address of the next instruction to be fetched and executed.

Besides IR and PC, there are n-general purpose registers R0 through

Rn-1. The other two registers which facilitate communication with memory are: -

1. MAR – (Memory Address Register):- It holds the address of the location to

be accessed. 2. MDR – (Memory Data Register):- It contains the data to be written into or

read out of the address location.

Operating steps are 1. Programs reside in the memory & usually get these through the I/P unit. 2. Execution of the program starts when the PC is set to point at the first

instruction of the program. 3. Contents of PC are transferred to MAR and a Read Control Signal is sent to

the memory. 4. After the time required to access the memory elapses, the address word is

read out of the memory and loaded into the MDR. 5. Now contents of MDR are transferred to the IR & now the instruction is

ready to be decoded and executed. 6. If the instruction involves an operation by the ALU, it is necessary to obtain

the required operands. 7. An operand in the memory is fetched by sending its address to MAR &

Initiating a read cycle. 8. When the operand has been read from the memory to the MDR, it is

transferred from MDR to the ALU. 9. After one or two such repeated cycles, the ALU can perform the desired

operation. 10. If the result of this operation is to be stored in the memory, the result is sent

to MDR. 11. Address of location where the result is stored is sent to MAR & a write cycle

is initiated. 12. The contents of PC are incremented so that PC points to the next instruction

that is to be executed.

Normal execution of a program may be preempted (temporarily interrupted)

if some devices require urgent servicing, to do this one device raises an Interrupt signal.

An interrupt is a request signal from an I/O device for service by the

processor. The processor provides the requested service by executing an appropriate interrupt service routine.

The Diversion may change the internal stage of the processor its state must

be saved in the memory location before interruption. When the interrupt-routine

service is completed the state of the processor is restored so that the interrupted

program may continue.

Bus structure: - The simplest and most common way of interconnecting various parts of the

computer. To achieve a reasonable speed of operation, a computer must be organized

so that all its units can handle one full word of data at a given time.

A group of lines that serve as a connecting port for several devices is called

a

bus.

In addition to the lines that carry the data, the bus must have lines for

address and control purpose.

Simplest way to interconnect is to use the single bus as shown

Since the bus can be used for only one transfer at a time, only two units can

actively use the bus at any given time. Bus control lines are used to arbitrate

multiple requests for use of one bus.

Single bus structure is

Low cost

Very flexible for attaching peripheral devices

Multiple bus structure certainly increases, the performance but also increases the cost significantly.

All the interconnected devices are not of same speed & time, leads to a bit of a problem. This is solved by using cache registers (ie buffer registers). These

buffers are electronic registers of small capacity when compared to the main memory but of comparable speed.

The instructions from the processor at once are loaded into these buffers and then the complete transfer of data at a fast rate will take place.

Performance: - The most important measure of the performance of a computer is how

quickly it can execute programs. The speed with which a computer executes

program is affected by the design of its hardware. For best performance, it is necessary to design the compiles, the machine instruction set, and the hardware in a

coordinated way.

The total time required to execute the program is elapsed time is a measure

of the performance of the entire computer system. It is affected by the speed of the processor, the disk and the printer. The time needed to execute a instruction is called

the processor time.

Just as the elapsed time for the execution of a program depends on all units

in a computer system, the processor time depends on the hardware involved in the execution of individual machine instructions. This hardware comprises the processor

and the memory which are usually connected by the bus as shown in the fig c.

Cache

Main Processor

Memory

Memory

Bus

Fig d :The processor cache

The pertinent parts of the fig. c is repeated in fig. d which includes the cache

memory as part of the processor unit.

Let us examine the flow of program instructions and data between the

memory and the processor. At the start of execution, all program instructions and the

required data are stored in the main memory. As the execution proceeds, instructions

are fetched one by one over the bus into the processor, and a copy is placed in the

cache later if the same instruction or data item is needed a second time, it is read

directly from the cache.

The processor and relatively small cache memory can be fabricated on a single IC chip. The internal speed of performing the basic steps of instruction

processing on chip is very high and is considerably faster than the speed at which the instruction and

data can be fetched from the main memory. A program will be executed faster if the movement of instructions and data between the main memory and the processor is

minimized, which is achieved by using the cache.

For example:- Suppose a number of instructions are executed repeatedly over a short period of time as happens in a program loop. If these instructions are available in the

cache, they can be fetched quickly during the period of repeated use. The same applies to the data that are used repeatedly.

Processor clock: - Processor circuits are controlled by a timing signal called clock. The clock

designer the regular time intervals called clock cycles. To execute a machine

instruction the processor divides the action to be performed into a sequence of basic

steps that each step can be completed in one clock cycle. The length P of one clock

cycle is an important parameter that affects the processor performance.

Processor used in today’s personal computer and work station have a clock

rates that range from a few hundred million to over a billion cycles per second.

Basic performance equation: - We now focus our attention on the processor time component of the total

elapsed time. Let ‘T’ be the processor time required to execute a program that has

been prepared in some high-level language. The compiler generates a machine language object program that corresponds to the source program. Assume that complete execution of

the program requires the execution of N machine cycle language instructions. The number N is the actual number of instruction execution and is not necessarily equal

to the number of machine cycle instructions in the object program. Some instruction

may be executed more than once, which in the case for instructions inside a program loop others may not be executed all, depending on the input data used.

Suppose that the average number of basic steps needed to execute one

machine cycle instruction is S, where each basic step is completed in one clock cycle. If clock

rate is ‘R’ cycles per second, the program execution time is given by

N S T

R this is often referred to as the basic performance equation.

We must emphasize that N, S & R are not independent parameters changing

one may affect another. Introducing a new feature in the design of a processor will lead to improved performance only if the overall result is to reduce the value of T.

Pipelining and super scalar operation: - We assume that instructions are executed one after the other. Hence the

value of S is the total number of basic steps, or clock cycles, required to execute one instruction. A substantial improvement in performance can be achieved by overlapping the execution of successive instructions using a technique called pipelining.

Consider Add R1 R2 R3

This adds the contents of R1 & R2 and places the sum into R3.

The contents of R1 & R2 are first transferred to the inputs of ALU. After the

addition operation is performed, the sum is transferred to R3. The processor can read the next instruction from the memory, while the addition operation is being performed. Then of that instruction also uses, the ALU, its operand can be transferred to the ALU inputs at the same time that the add instructions is being

transferred to R3.

In the ideal case if all instructions are overlapped to the maximum degree

possible the execution proceeds at the rate of one instruction completed in each

clock cycle. Individual instructions still require several clock cycles to complete.

But for the purpose of computing T, effective value of S is 1.

A higher degree of concurrency can be achieved if multiple instructions

pipelines are implemented in the processor. This means that multiple functional

units are used creating parallel paths through which different instructions can be

executed in parallel with such an arrangement, it becomes possible to start the

execution of several instructions in every clock cycle. This mode of operation is

called superscalar execution. If it can be sustained for a long time during program

execution the effective value of S can be reduced to less than one. But the parallel

execution must preserve logical correctness of programs, that is the results produced

must be same as those produced by the serial execution of program instructions.

Now a days may processor are designed in this manner. Clock rate:- These are two possibilities for increasing the clock rate ‘R’.

1. Improving the IC technology makes logical circuit faster, which reduces the

time of execution of basic steps. This allows the clock period P, to be reduced and the clock rate R to be increased.

2. Reducing the amount of processing done in one basic step also makes it

possible to reduce the clock period P. however if the actions that have to be

performed by an instructions remain the same, the number of basic steps

needed may increase.

Increase in the value ‘R’ that are entirely caused by improvements in IC

technology affects all aspects of the processor’s operation equally with the

exception of the time it takes to access the main memory. In the presence of cache the percentage of accesses to the main memory is small. Hence much of the performance gain excepted from the use of faster technology can be realized.

Instruction set CISC & RISC:- Simple instructions require a small number of basic steps to execute.

Complex instructions involve a large number of steps. For a processor that has only simple

instruction a large number of instructions may be needed to perform a given

programming task. This could lead to a large value of ‘N’ and a small value of ‘S’

on the other hand if individual instructions perform more complex operations, a fewer instructions will be needed, leading to a lower value of N and a larger value of S. It is not obvious if one choice is better than the other.

But complex instructions combined with pipelining (effective value of S 1)

would achieve one best performance. However, it is much easier to implement

efficient pipelining in processors with simple instruction sets.

Performance measurements:- It is very important to be able to access the performance of a computer,

comp designers use performance estimates to evaluate the effectiveness of new features.

The previous argument suggests that the performance of a computer is given

by the execution time T, for the program of interest.

Inspite of the performance equation being so simple, the evaluation of ‘T’ is

highly complex. Moreover the parameters like the clock speed and various

architectural features are not reliable indicators of the expected performance.

Hence measurement of computer performance using bench mark programs

is done to make comparisons possible, standardized programs must be used.

The performance measure is the time taken by the computer to execute a given bench mark. Initially some attempts were made to create artificial programs

that could be used as bench mark programs. But synthetic programs do not properly predict the performance obtained when real application programs are run.

A nonprofit organization called SPEC- system performance evaluation

corporation selects and publishes bench marks.

The program selected range from game playing, compiler, and data base applications to numerically intensive programs in astrophysics and quantum

chemistry. In each case, the program is compiled under test, and the running time on a real computer is measured. The same program is also compiled and run on one

computer selected as reference.

The ‘SPEC’ rating is computed as follows.

Running time on the reference computer

SPEC rating =

Running time on the computer under test

If the SPEC rating = 50

Means that the computer under test is 50 times as fast as the ultra sparc 10. This is repeated for all the programs in the SPEC suit, and the geometric mean of the

result is computed.

Let SPECi be the rating for program ‘i’ in the suite. The overall SPEC

rating for the computer is given by 1

n

n

SPEC rating = SPECi

i 1

Where ‘n’ = number of programs in suite.

Since actual execution time is measured the SPEC rating is a measure of the combined effect of all factors affecting performance, including the compiler, the OS,

the processor, the memory of comp being tested.

Multiprocessor & microprocessors:- Large computers that contain a number of processor units are called

multiprocessor system.

These systems either execute a number of different application tasks in parallel or execute subtasks of a single large task in parallel.

All processors usually have access to all memory locations in such system & hence they are called shared memory multiprocessor systems.

The high performance of these systems comes with much increased complexity and cost.

In contrast to multiprocessor systems, it is also possible to use an interconnected

group of complete computers to achieve high total computational power. These

computers normally have access to their own memory units when the tasks they are

executing need to communicate data they do so by exchanging messages over a

communication network. This properly distinguishes them from shared memory

multiprocessors, leading to name message-passing multi computer.

CPU

Alternatively referred to as the brain of the computer, processor, central

processor, or microprocessor, the CPU (pronounced as C-P-U), short for Central

Processing Unit, was first developed at Intel with the help of Ted Hoff in the early

1970's. The computer CPU is responsible for handling all instructions it receives

fromhardware and software running on the computer.

Note: Many new computer users may improperly call their computer and sometimes

their monitor the CPU. When referring to your computer or monitor, it is proper to

refer to them as either the "computer" or "monitor" and not a CPU.

The picture below is an example of what the top and bottom of

an Intel Pentiumprocessor looks like. The processor is placed and secured into a

compatible CPU socketfound on the motherboard and, because of the heat it

produces, it is covered with a heat sink to help keep it cool and running smoothly.

As you can see in the above picture, the CPU chip is usually in the shape of a

square or rectangle and has one notched corner to help place the chip properly into

the CPU socket. On the bottom of the chip are hundreds of connector pins that plug

into each of the corresponding holes in the socket. Today, most CPU's resemble the

picture shown above; however, Intel and AMD have also experimented with slot

processors that were much larger and slid into a slot on the motherboard. Also, over

the years there have been dozens of different types of sockets on motherboards.

Each socket only supports specific types of processors and each has its own pin

layout.

Components of the CPU

In the CPU, the primary components are the ALU (Arithmetic Logic Unit) that

performs mathematical, logical, and decision operations and the CU (Control Unit)

that directs all of the processors operations.

Over the history of computer processors, the speed (clock speed) and capabilities of

the processor have dramatically improved. For example, the first microprocessor

was the Intel 4004 that was released November 15, 1971 and had

2,300 transistors and performed 60,000 operations per second. The

Intel Pentium Processor pictured above has 3,300,000 transistors and performs

around 188,000,000 instructions per second.

Types of CPUs

There are two main types of CPUs found in computers today: 32-bit and 64-bit. In

addition to this, CPUs can be broken down into types based on the manufacturer and

version as well.

Below is a list of the more common types of CPUs for home or business computers,

in chronological order of release by manufacturer.

Note: There are multiple versions for some of these CPU types.

Intel processors

The AMD Opteron series and Intel Xeon series are two common types of CPUs for

servers and some workstation computers.

Some mobile devices, like smartphones and tablets, use ARM CPUs. These CPUs

are smaller in size, require less power and generate less heat.

MEMORY TYPES Two basic types:

ROM : Read-only memory

RAM : Read-Write memory

Four commonly used memories:

ROM

Flash (EEPROM)

Static RAM (SRAM)

Dynamic RAM (DRAM)

Generic pin configuration:

Memory Chips

The number of address pins is related to the number of memory locations .

Common sizes today are 1K to 256M locations.

Therefore, between 10 and 28 address pins are present.

The data pins are typically bi-directional in read-write memories.

The number of data pins is related to the size of the memory location .

For example, an 8-bit wide (byte-wide) memory device has 8 data pins.

Catalog listing of 1K X 8 indicate a byte addressable 8K memory.

Each memory device has at least one chip select ( CS ) or chip enable ( CE )

or select ( S ) pin that enables the memory device.

This enables read and/or write operations.

If more than one are present, then all must be 0 in order to perform a read or

write.

Memory Chips

Each memory device has at least one control pin.

For ROMs, an output enables (OE) or gate (G) is present.

The OE pin enables and disables a set of tristate buffers.

For RAMs, a read-write (R/W) or write enable (WE) and read enable (OE)

are present.

For dual control pin devices, it must be hold true that both are not 0 at the

same time.

ROM:

Non-volatile memory: Maintains its state when powered down.

There are several forms:

ROM: Factory programmed, cannot be changed. Older style.

PROM: Programmable Read-Only Memory.

Field programmable but only once.

Older style.

EPROM: Erasable Programmable Read-Only Memory.

Reprogramming requires up to 20

minutes of high-intensity UV light

exposure.

Memory Chips

ROMs (cont):

Flash EEPROM: Electrically Erasable Programmable ROM.

Also called EAROM (Electrically

Alterable ROM) and NOVRAM(NOn-

Volatile RAM).

Writing is much slower than a normal

RAM.

Used to store setup information, e.g.

video card, on computer systems.

Can be used to replace EPROM for

BIOS memory.

EPROMs

Intel 2716 EPROM (2K X 8):

EPROMs

2716 Timing diagram:

Sample of the data sheet for the 2716 A.C. Characteristics.

Symbol Parameter Limits

Unit Test Condition Min Typ. Max

tACC1 Addr. to Output Delay 250 450 ns PD/PGM= CS

=VIL

tOH Addr. to Output Hold 0 ns PD/PGM= CS

=VIL

tDF Chip Deselect to Output

Float 0 100 ns PD/PGM=VIL

... ... ... ... ... ... ...

This EPROM requires a wait state for use with the 8086

( 460ns constraint).

SRAMs

TI TMS 4016 SRAM (2K X 8):

Virtually identical to the EPROM with respect to the pinout.

However, access time is faster (250ns).

o See the timing diagrams and data sheets in text.

SRAMs used for caches have access times as low as 10ns .

DRAMs

DRAM:

SRAMs are limited in size (up to about 128K X 8).

DRAMs are available in much larger sizes, e.g., 64M X 1.

DRAMs MUST be refreshed (rewritten) every 2 to 4 ms

Since they store their value on an integrated capacitor that loses charge over

time.

This refresh is performed by a special circuit in the DRAM which refreshes

the entire memory using 256 reads.

Refresh also occurs on a normal read, write or during a special refresh cycle.

More on this later.

The large storage capacity of DRAMs make it impractical to add the required

number of address pins.

Instead, the address pins are multiplexed .

DRAMs

TI TMS4464 DRAM (64K X 4):

The TMS4464 can store a total of 256K bits of data.

It has 64K addressable locations which means it needs 16 address inputs, but

it has only 8 .

The row address (A 0 through A 7 ) are placed on the address pins and

strobed into a set of internal latches.

The column addres (A 8 through A 15 ) is then strobed in using CAS.

DRAMs

TI TMS4464 DRAM (64K X 4) Timing Diagram:

o CAS also performs the function of the chip select

input.

DRAMs

Larger DRAMs are available which are organized as 1M X 1 , 4M X 1 , 16M

X 1 , 64M X 1(with 256M X 1 available soon).

DRAMs are typically placed on SIMM (Single In-line Memory Modules)

boards.

30-pin SIMMs come in 1M X 8 , 1M X 9 (parity), 4M X 8 , 4M X 9 .

72-pin SIMMs come in 1 / 2 / 3 / 8 / 16M X 32 or 1M X 36 (parity).

DRAMs

Pentiums have a 64-bit wide data bus.

The 30-pin and 72-pin SIMMs are not used on these systems.

Rather, 64-bit DIMMs (Dual In-line Memory Modules) are the standard.

These organize the memory 64-bits wide.

The board has DRAMs mounted on both sides and is 168 pins.

Sizes include 2M X 64 (16M), 4M X 64 (32M), 8M X 64 (64M) and 16M X

64 (128M).

The DIMM module is available

in DRAM, EDO and SDRAM (and NVRAM) with and without an

EPROM.

The EPROM provides information abou the size and speed of the memory device

for PNP applications.

INPUT DEVICES

An input device for a computer allows you to enter information. The most

fundamental pieces of information are keystrokes on a keyboard and clicks with a

mouse. These two input devices are essential for you to interact with your computer.

Many other input devices exist for entering other types of information, such as

images, audio and video. Input devices represent one type of computer peripheral -

the other two types are output devices and storage devices.

Examples of Input Devices

A keyboard is the most fundamental input device for any computer system. In the

early days of computing, it was typically the only input device. A keyboard contains

keys for letters and numbers as well as for specialized tasks, such as Enter, Delete,

etc.

Typical keyboard for a desktop computer

When operating systems started to use graphical user interface (GUI), the mouse

was developed as a pointing device. Typically, a mouse resides on a flat surface, and

by moving the mouse, you can move the pointer on the screen. One or more buttons

on the mouse allow you to enter instructions by clicking. Most models also include a

wheel for scrolling.

Typical mouse for a desktop computer

Desktop computers have a separate keyboard and mouse, but for laptops, these are

integrated into a computer system itself. In laptops, the mouse is actually substituted

with a touchpad or trackpad. This is a specialized surface that follows the motion of

your finger. You can still connect an external mouse to a laptop if you prefer.

Keyboard and trackpad on a laptop computer

Another common input device is an image scanner. A typical desktop or flatbed

scanner is a device that optically scans printed images and paper documents and

converts them into digital images. In most scanners, you place the document on a

glass plate and place an opaque cover over it. A bright light moves across the image,

and the reflection is captured by a sensor, which converts the document to a digital

image.

Flatbed scanner

Audio and video can be recorded using a microphone and video camera,

respectively. Due to the popularity of video conferencing using services like Skype,

these are now typically integrated in most laptops and monitor displays for desktops;

however, you can also connect an external webcam, which can record both audio

and video.

External webcam for video conferencing

DISPLAY DEVICES

A display device is an output device for presentation of information in visual or

tactile form (the latter used for example in tactile electronic displays for blind

people). When the input information is supplied as an electrical signal, the display is

called an electronicdisplay.

Cathode Ray Tube (CRT)

Electron gun = cathode + control grid

Pixel ratio = height of pixel width of pixel

Aspect ratio = # rows in display __# columns in display

Resolution -- Number of pixels per linear distance (e.g., 640 × 400-pixel

display).

COLOR -- 3 different phosphors + 3 different gusns (e.g., red, green, and blue)

Phosphore

The electron beam causes the phosphor’s atoms to move into

higher energy state

The atoms give off energy as light when they return to their stable state

REFRESHMENT

Persistence -- Time for emitted light to fade by 90% of its intensity

(normally 10 to 60 microseconds).

Refresh -- Redrawing of an image to preserve it on a screen

Refresh rate -- Number of times per second the image is redrawn

(normally > 60 Hz)

Flicker -- Develops in low refresh rate because the eyes can not integrate the

individual light impulses comming from a pixel.

Critical fushion frequency -- Refresh rate above which a picture stops

flickering and fuses into a steady image. Depends on

o Phosphor’s persistence

o Image intensity

o Ambient room lighting

o Wavelenght of emitted light

o The observer

Raster Display

SYSTEM COMPONENTS

The screen is subdivided into a matrix of pixels (smallest addressable units).

Raster scanline -- A line of pixels along the screen

Frame (refresh) buffer -- Block of memory used to store the screen pattern

HOW IT WORKS

The DISPLAY PROCESSOR produces the raster image in the frame buffer

from the commands

The VIDEO CONTROLLER moves the beam row wise across the pixels

setting it on and off according to the content of theframe buffer

The display must be refreshed to avoid flickering (raster image redisplayed

30 to 60 times pers second)

2-BIT BLACK-AND-WHITE GRAY LEVEL

00 0 3 of full intensity

01 1 3 of full intensity

10 2 3 of full intensity

11 3 3 of full intensity

FRAME BUFFER

Single-bit black-and-white frame buffer (monochrome, bitmap)

N-bit black-and-white gray level frame buffer (pixmap)

N-bit black-and-white gray level frame buffer with M-bit lookup table

N-bit color frame buffer with M-bit look-up table (typically N = 8 and M =

24)

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WHY USE A LOOK-UP TABLE?

Reduced memory for full array of colors

24 bit color * 1280 by 1024 resolution/ 8 bits per byte 4MB

Color table animation

2-BIT BLACK-AND-WHITE GRAY LEVEL FRAME BUFFER WITH 8-

BIT LUT

2-bit color level frame buffer with 24-bit LUT (e.g., RGB: red, green, blue)

Vector (or Random Scan) Display

Images are described in terms of line segments rather than pixels.

Display processor cycles through the commands

Advatages / Disadvantages

HARD COPY DEVICES

Hard copy devices are used for draw a graphical image or another information on to

the paper. Mainly two types of hard copy devices namely printer and plotter that can

be used for print image,line or charater on to the paper.

Hard-Copy Devices

We can obtain hard-copy output for our images in several formats. For

presentations or archiving, we can send image files to devices or service bureaus that

will produce 35-mm slides or overhead transparencies. To put images on film, we

can simply photograph a scene displayed on a video monitor. And we can put our

pictures on paper by directing graphics output to a printer or plotter.

The quality of the pictures obtained from a device depends on dot size and the

number of dots per inch, or lines per inch, that can be displayed. To produce smooth

characters in printed text strings, higher-quality printers shift dot positions so that

adjacent dots overlap.

Printers produce output by either impact or nonimpact methods. Impact printers

press formed character faces against an inked ribbon onto the paper. A line printer is

an example of an impact device, with the typefaces mounted on bands, chains,

drums, or wheels. Nonimpact printers and plotters use laser techniques, ink-jet

sprays, xerographic processes (as used in photocopying machines), electrostatic

methods, and electrothermal methods to get images onto paper.

Character impact printers often have a dot-matrix print head containing a

rectangular array of protruding wire pins, with the number of pins depending on the

quality of the printer. Individual characters or graphics patterns are obtained by

retracting certain pins so that the remaining pins form the pattern to be printed.

Figure 2-58 shows a picture printed on a dot-matrix printer.

Figure :1 A picture generated on a dot-

matrix printer showing how the

density of the dot patterns can

be varied to produce light and

dark areas. (Courtesy of Apple

Computer, Inc.)

In a laser device, a laser beam mates a charge distribution on a rotating drum coated with a

photoelectric material, such as selenium. Toner is applied to the drum and then transferred to

paper. Figure 2-59 shows examples of desktop laser printers with a resolution of 360 dots per

inch.

Figure :2 Small-footprint laser printers. (Courtesy of Texas Instruments.)

Figure :3 A 360-dot-per-inch desktop ink-jet plotter. (Courtesy of Summagraphics Corporation.)

Ink-jet methods produce output by squirting* ink in horizontal rows across a roll of paper

wrapped on a drum. The electrically charged ink stream is deflected by an electric field to

produce dot-matrix patterns. A desktop ink-jet plotter with a resolution of 360 dots per inch is

shown in Fig. 3, and examples of larger high-resolution ink-jet printer/plotters are shown in

Fig.4

Figure :4 Floor-model, ink-jet color printers that use variable dot size to achieve an

equivalent resolution of 1500 to 1800 dots per inch.

An electrostatic device places a negative charge on the paper, one complete row at a time

along the length of the paper. Then the paper is exposed to a toner. The toner is positively

charged and so is attracted to the negatively charged areas, where it adheres to produce the

specified output. A color electrostatic printer/plotter is shown in Fig. 2-62. Electrothermal

methods use heat in a dot-matrix print head to output patterns on heat-sensitive paper.

Figure :5 An electrostatic printer that can display 400

dots per inch.

We can get limited color output on an impact printer by using different-colored ribbons.

Nonimpact devices use various techniques to combine three color pigments (cyan, magenta, and

yellow) to produce a range of color patterns. Laser and xerographic* devices deposit the three

pigments* on separate passes; ink-jet methods shoot the three colors simultaneously on a single

pass along each print tine on the paper.

STORAGE DEVICES

What are Storage devices?

Storage Devices are the data storage devices that are used in the computers to store

the data. The computer has many types of data storage devices. Some of them can be

classified as the removable data Storage Devices and the others as the non removable

data Storage Devices.

The memory is of two types; one is the primary memory and the other one is

the secondary memory.

The primary memory is the volatile memory and the secondary memory is the non

volatile memory. The volatile memory is the kind of the memory that is erasable and

the non volatile memory is the one where in the contents cannot be erased. Basically

when we talk about the data storage devices it is generally assumed to be the

secondary memory.

The secondary memory is used to store the data permanently in the computer.

The secondary storage devices are usually as follows: hard disk drives – this is the

most common type of storage device that is used in almost all the computer systems.

The other ones include the floppy disk drives, the CD ROM, and the DVD ROM.

The flash memory, the USB data card etc.

Find out more ... Navigate through the list of storage devices given on the right side.

Floppy discs:

A floppy disk is a data storage medium that is composed of a disk of thin, flexible

floppy)magnetic storagemedium encased in asquareor rectangularplasticshell. Floppy

disks are read and written by afloppy disk drive.

Application

Any use where small files such as word processing, small spreadsheets and databases

need to be moved from one computer to another.

Useful to backup small data files.

Fixed hard discs

A hard disk drive is the device used to store large amounts of digital information in

computers and related equipment like iPods and games consoles such as the Xbox

360 and PS3.

Hard disk drives are used to store operating systems, software and working data.

These are suitable for any application which requires very fast access to data for

both reading and writing to. However, Hard disk drives may not be suitable for

applications which need portability.

Almost all computers used a fixed hard disc. Used for on-line and real time processes

requiring direct access. Used in file servers for computer networks to store large

amount of data.

Portable hard discs

Portable hard discs are good fun because you can carry data about all over the place

and transfer information, programs, pictures, etc between computers.

Advantages:

Greatly improved data cargo carrying capacity (relative to the 1.44 Mb floppy disc).

You don't need to worry about the other person having the same type of special

cartridge drive as yourself.

Disadvantages:

Hard drives have to be handled quite carefully, and when being transported should be

wrapped in something soft and put in a padded bag.

More expensive than other forms of removable media.

Application

Portable disc discs are used to store very large files which need transporting from

one computer to another and price is not an issue.

Magnetic tapes

Magnetic tape has been used for data storage for over 50 years. When storing large

amounts of data, tape can be substantially less expensive than disk or other data

storage options. Tape storage has always been used with large computer systems.

Modern usage is primarily as a high capacity medium for backups and archives.

Drawbacks

Writing and retrieving data is slow.

It uses serial access for reading and writing.

Application

Magnetic tapes are used for application which requires extremely large storage

capacity where speed of access is not an issue.

It is commonly used for backups of file servers for computer networks, in a variety

of batch processing applications such as reading of bank cheques, payroll processing

and general stock control.

Optical backing storage media such as CDs andDVDs

CDs tend to be used for large files (but smaller than 1Gb) which are too big for a

floppy disc to hold such as music and general animation.

DVDs are used to hold very large files (several Gb) such as movie films. Both CDs

and DVDs are portable i.e. they can be transported from one computer to another.

Both can be used to store computer data.

CD ROM/DVD ROM Applications which require the prevention of deletion of data,

accidental or otherwise. CDs used by software companies for distributing software

programs and data; by Music companies for distributing music albums and by book

publishers for distributing encyclopaedias, reference books etc. DVDs used by film

distributors.

CD R/DVD R Applications which require a single ‘burning’ of data, e.g. CDs -

recording of music downloads from the Internet, recording of music from MP3

format, recording of data for archiving or backup purposes. DVDs – recording of

film movies and television programs.

CD RW/DVD RW Applications which require the updating of information and

ability to record over old data. Not suitable for music recording but is very useful for

keeping generations of files. DVDs have between five and ten times the capacity of

CDs.

Solid state backing storage

These are the smallest form of memory available in the market today.

Widely used as removable storage.

They are more robust than other forms of storage.

Though expensive than other forms they can be easily written to and updated.

Memory sticks/Pen drives

USB flash drives are typically removable and rewritable, much smaller than a floppy

disk. Storage capacities typically range from 64 MB to 64 GB. USB flash drives

offer potential advantages over other portable storage devices, particularly the floppy

disk.

They have a more compact shape, operate faster, hold much more data, have a more

durable design, and operate more reliably due to their lack of moving parts. Flash

drives are widely used to transport files and backup data from computer to computer.

Flash memory cards

A memory card or flash memory card is a solid-state electronic flash memory data

storage device used with digital cameras, handheld and Mobile computers,

telephones, music players, video game consoles, and other electronics.

Nowadays, most new PCs have built-in slots for a variety of memory cards; Memory

Stick, CompactFlash, SD, etc. Some digital gadgets support more than one memory

card to ensure compatibility.