It305 01 Introduction

8/22/2019 It305 01 Introduction

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Introduction


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Motivation A computeris the combination of two distinct parts:

Computer hardware is the collection of physicalelements that comprise a computer system

Computer software refers to the programs installed on

that hardware

This course is about the hardware of the computers.What the hardware components within a computer

are, how those components are built, how they

communicate, and eventually how the computer

hardware works. Knowing how the hardware works

will help you understand how the software works as

well.

Knowing at least something on even if not much details

about the hardware of the toy you are using will probably

make you a better professional.


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Signal vs. Data Data: formatted information

examples: voice, music, image, file Signal: electric, electromagnetic, or light representation of

data

To be transmitted, data must be turned into energy

in the form of electro-magnetic signals or light etc.


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Analog vs. Digital Data Analog data take on continuous values in some interval

voice, temperature, etc. Digital data take on discrete (a finite / countable number

of) values in a given interval

text, digitized images, etc.


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Analog vs. Digital Data


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Transmission Impairments

Sent and received signals are not same not perfect pairs

Main types of transmission impairments:

Attenuation

Delay Distortion

Noise


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Transmission Impairments For analog signals, impairments can degrade signal

quality

For digital signals, impairments can cause bit errors


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Attenuation Attenuation is reduction / loss in signal power

When a signal travels through a medium, it loses some ofits energy

Main challenges in combating attenuation:

(1) received signal must have:

sufficient strength so that receiver can detectsignal

not too strong to overload transmitter / receiver

circuitry

(2) signal must maintain a level sufficiently higher thannoise, to be received without error


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Attenuation

To compensate for loss, analog amplifiers / digital

repeaters are used to boost the signal at regular intervals


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Delay Distortion

Delay Distortion: change in signals form / shape Each signal component has its own propagation speed

through a medium, and therefore, its own delay in arriving

at the final destination

Critical for composite (both analog and digital) signals


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Noise Noise: unwanted signals that get inserted / generated

somewhere between transmitter and receiver

Noise is the major limiting factor in communications

system performance

Presence of noise limits the reliability with which the

receiver can correctly determine the information that was

transmitted


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Problems with Analog Transmission

When analog signal is transmitted over long distance, it

becomes distorted due to annetuation, delay distortion,

noise, and possible interference

Transmitters are used to increase the amplitude

However, the noise will not be eliminated in the received

signal


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Digital Transmission Suppose that a string of 0s and 1s is conveyed by a

sequence of positive and negative voltages

A digital regenerator is used to recover the data from the

digital dignal


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How to transfer data? Digital devices, such as computers use bits to represent

data

Transmitting data means sending bits

Physically, communication system can use one of the

following energy types to transfer information:

1. electric current2. electromagnetic wave

3. light

How to encode bits?

Each bit is represented by a voltage, for example:

0 positive voltage

1 negative voltage


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Why Digital Transmission (Signal)? Most important reason:

Since only two values exist, less error occurs; hencecan travel long distance

Digital regeneratoreliminates the accumulation of noise

after subsequent usage of repeaters

Supporting reasons: Cheaper to send data, since easier to work with only

two values

Maintanence is cheaper


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Analog vs. Digital Signal

Analog signal: signal that is continuous in time and canassume an infinite number of values in a given range

continuous in time and value

Discrete (digital) signal signal that is continuous in time

and can assume only a limited number of values maintains a constant level and then changes to another

constant level


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Sampling Sampling is the reduction of a continuous signal to a

discrete signal.

In sampling data, available number of values (which is

actually infinite) in analog domain is mapped to a limited

number of values in digital domain.

It is converting unlimited / vast amount of values to limited

set of numbers.

The relation between floating point and integer numbers is

analogous to this. If you want to sample a set of floating

point values, say the values between 0.0 and 9.0, you may

create the sample values as {0, 1, 2, 3, 4, 5, 6, 7, 8, 9} ifthe sampling interval is 1. If you use 2 as the sampling

interval, the set of values becomes {0, 2, 4, 6, 8}.


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Sampling


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Computers are digital Computers are electronic circuits, so all they really

process is electricity.

To make it more precise, computers process the voltage of

the processed electricity.

Since it is so hard to work with analog systems, the

applied voltage to the computer is digitized by rounding

the voltage values.

Two voltages are applied to the computer: 0 and 5.

When the applied voltage is close to zero, it is assumed to

be zero and vice versa.

When part of a computer circuit carries a voltage of 5

volts, we say that it has a value of 1. When part of a circuit

carries zero voltage, we say that it has a value of 0. Its all

a matter of interpretation.


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Why is digital preferred?1. It is easier and much more practical to work on Digital

signals.

a. Once a signal is turned into a sequence of discrete

numbers, mathematical algorithms can be used to

operate on the digital data, whilst not on analog data.

b. Digital numbers can also be stored more compactly

than analog values.

2. If an analog signal is transmitted over long distances,

noise (erroneous change in the signal) attaches itself to

the signal, and is not practical if it is possible- to remove

the noise from an analog signal.


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Analog to Digital Converter (ADC) When some analog data is to be processed by the

computers, it is required to convert the analog data to

digital.

An analog-to-digital converter(ADC orA/D) is a device

that uses sampling to convert a continuous quantity to a

discrete time representation in digital form.

The reverse operation is performed by a digital-to-analog

converter (DAC).


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Period vs. Frequency Period is the duration of one cycle in a repeating event.

A lecture takes is 50 minutes; T = 50 m. Frequency is the number of occurrences of a repeating

event per unit time.

Heart beats 180 times a minute; f = 180 times / min.

T . f = 1. Hertz symbolizes count per second.

f = 180 times / min = 180/60 Hz. = 3 Hz.


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What is a computer? A computeris a general-purpose device that can be

programmed to carry out a set of arithmetic and logical

operations.

Any problem can be mapped into a set of logical and

arithmetical operations; hence a computer can practically

solve all problems.


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Abstraction Levels of computers.


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Abstract view of a computer


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Computer Classification by size Microcomputer / personal computer

Desktop Dedicated computers

Car navigation systems

Embedded computers

Mobile devices Laptops, notebooks, palmtops

Tablets

Smartphones, PDAs

Game consoles

Mini computer

Mainframe computer

Super computer


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Computer Classification by function Supercomputers

Servers A computer that is dedicated to provide a service

Workstations

Serve single user with additional hardware

Embedded computers Specific control functions within larger system

Operate continuously without being reset or rebooted

Once employed the software is not modified

Smart phones / PDAs

PDA functions as a personal information manager

A Smartphone is a mobile phone with additional

computing capability and connectivity


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Theoretical History of Computers Early computing machines had fixed programs.

Reprogramming was a laborious process ENIAC required 3 weeks to load a program

A stored-program computer keeps programs and data in

read-write, random-access memory (RAM)

Alan Turing described a hypothetical machine is known asTuring Machine in 1936

Von Neumann architecture proposed by Von Neumann


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Von Neumann architecture


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Modified Von Neumann architecture


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Von Neumann bottleneck Neumann bottleneck is the limited throughput (data

transfer rate) between CPU and memory

Since program memory and data memory cannot be

accessed at the same time, throughput is much smaller

than the rate at which the CPU can work

This limits the effective processing speed of CPU

CPU is continuously forced to wait for needed data to be

transferred to or from memory

Since CPU speed and memory size have increased much

faster than the throughput between them, the bottleneck

has become more of a problem, a problem whose severity

increases with every newer generation of CPU.


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Harvard architecture Harvard architecture features separate places for:

instruction memory data memory.

With this type of a design, both data and instructions could

be operated on independently.

Another subtle difference is that Von Neumannarchitecture permits self-modifying programs, whereas

Harvard architecture does not.

Since the same memory space in the von Neumann

architecture may hold data and program code, it ispossible for an instruction to change the instruction in

another portion of the code space.

In the Harvard Architecture, loads and stores can only

occur in the data memory, so self-modifying code is harder


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Harvard Architecture


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Harvard Architecture


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Technical History of Computers1. First Generation: Vacuum Tube Computers

(19451953)2. Second Generation: Transistorized Computers

(19541965)

3. Third Generation: Integrated Circuit Computers

(19651980)4. Fourth Generation: VLSI Computers

(1980 )


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Technical History of Computers1. Vacuum Tube

2. Transistor3. Chip

4. Integrated circuit


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1. Vacuum Tube (19451953) During World War II, the army had an insatiable need for

calculating the trajectories of its new ballistic armaments

Thousands of human computers were engaged around

the clock cranking through the arithmetic required for

these firing tables

Realizing that an electronic device could shorten ballistic

table calculation from days to minutes, the army funded

the ENIAC


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ENIAC ENIAC shorten the time to calculate a table from 20 hours

to 30 seconds

ENIAC had shown that vacuum tube computers were fast

and feasible

During the next decade, vacuum tube systems continued

to improve and were commercially successful

ENIAC is recognized as the first all-electronic, general-

purpose digital computer.

ENIAC used 17,468 vacuum tubes, occupied 180 meter

square of floor space, weighed 30 tons, and consumed

174 kilowatts of power

ENIAC had a memory capacity of about 1,000 information

bits (about 20 10-digit decimal numbers) and used

punched cards to store data.


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ENIAC


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Vacuum Tubes

V T b


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Vacuum Tubes A vacuum tube is a device controlling electric current

through a vacuum in a sealed container

The container is often thin transparent glass in a roughly

cylindrical shape

Vacuum tubes are used for rectification, amplification,

switching, or similar processing or creation of electrical

signals.

2 T i t (1954 1965)


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2. Transistor (19541965) The vacuum tube technology of the first generation was

not very dependable

Vacuum tube systems often experienced more downtime

than uptime

In 1948, three researchers with Bell Laboratories invented

the transistor

This new technology not only revolutionized devices such

as televisions and radios, but also pushed the computer

industry into a new generation

Because transistors consume less power than vacuum

tubes, are smaller, and work more reliably, the circuitry in

computers consequently became smaller and more

reliable

3 I t t d Ci it (1965 1980)


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3. Integrated Circuits (19651980) The real explosion came with IC (microchip) generation

Early ICs allowed dozens of transistors to exist on a single

silicon chip that was even smaller than a single transistor

Computers became faster, smaller, and cheaper, bringing

huge gains in processing power.

IC is an electronic circuit manufactured into the surface ofa semiconductor material

Discrete circuit is an electronic circuit built out of

discrete components, such as resistors, transistors,

etc., instead of a single integrated circuit.

The integration of large numbers of tiny transistors into a

small chip was an enormous improvement over the

manual assembly of circuits using discrete electronic

components

Ad t f IC


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Advantages of IC1. Cost is low because

the chips, with all their components, are printed as a

unit rather than being constructed one transistor at a

time

much less material is used to construct a packaged IC

die than to construct a discrete circuit.

2. Performance is high because the components switch

quickly and consume little power as a result of the small

size and close proximity of the components

4 VLSI C t (1980 )


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4. VLSI Computers (1980 - ) VLSI (Very Large-Scale Integration) enabled several

billion transistors on an IC

Multiple developments were required to achieve this

increased density

Smaller design rules

Cleaner fabrication facilities

H d C t f C t


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Hardware Components of Computers


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