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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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Questions?