Computer Components
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Scanner
CPU (Microprocessor)
Main memory (RAM)
Expansion cards
Power supply unit
Optical disc drive
Hard disk drive (HDD)
Motherboard
Speaker
Monitor
System software
Application software
Keyboard
Mouse
External hard disk
Printer
Data Storage
Introduction to Computer and Internet
Outline
•Introduction
•Bits and their storage
•Boolean operations
•Gates
•Main memory
•Memory organization
•Mass storage
Introduction to Computer and Internet
Introduction
•We begin our study of computer science by
considering how information is encoding and
stored inside computers
Introduction to Computer and Internet
Bits And Their Storage
•Inside the computers information is encoded as
patterns of 0s and 1s. These digits are called bits
(binary digits).
•bits are used to represent:
•Numeric values
•Characters
•Images
•Sounds
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Boolean Operations
•bit 0 represent the value false
•bit 1 represent the value true
•Operations that manipulate true/false values are
called Boolean operations.
•basic Boolean operations are:
•AND, OR, and XOR (exclusive or)
•There is also NOT
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Boolean Operations
•AND, OR, and XOR operators take two operands,
but the NOT operator takes a single operand
•AND
•The AND operator performs logical
conjunction on two Boolean expressions.
•If both expressions are equal to true (1), then
the AND return true, otherwise all other cases
should produce an output False (0)
Input1 Input2 output
Truth Table
0
0
0
0
1
0
1
0
0
1
1
1
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Boolean Operations
•OR
•The OR operator performs logical disjunction on
two Boolean expressions.
•OR operator returns true value when at least one
of their Boolean expression is equal to true.
Input1
Truth Table
Input2 output
0
0
0
0
1
1
1
0
1
1
1
1
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Boolean operations
•XOR (exclusive or)
•XOR performs logical exclusion on two expressions.
•XOR produce an output of 1 (true) when one of its
inputs is 1 and the other is 0
•(In short, the XOR operation produces an output of
1 when its input are different)
Truth Table
Input1
Input2
output
0
0
0
0
1
1
1
0
1
1
1
0
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Boolean Operations
•NOT
•The operation NOT is another Boolean operation.
It differs from AND, OR, and XOR because it has
only one input.
•Its output is the opposite of that input.
Truth Table
Input
Output
0
1
1
0
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Gates And Flip-flops
•Gate is a device that produces the output of a
Boolean operation.
•Its often implemented as (small) electronic circuits,
in which the digits 0 and 1 are represented as
voltage levels.
•Gates provides the building blocks from which
computer are constructed.
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Gates
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Exercise
•What input bit patterns will cause the following
circuits to produce an output of 1?
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Main Memory
•For storing data, a computer contains a large
collection of circuits, each capable of storing a
single bit.
•Also known as RAM “Random Access Memory”
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Memory Organization
• A computer main memory is organized in
manageable units called cells.
• Cell: A unit of main memory (typically 8 bits
which is one byte)
• Each cell’s size equal to eight (8) bits.
• higher-order end: the left end of the row of bits
on the memory
• lower-order end: the right end
• most significant bit: the last bit at the high-order
end.
• least significant bit: the bit at the right end.
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Memory Organization
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Memory Organization
•To identify individual cell in a computer’s main
memory, each cell is assigned a unique “name”,
called its address.
•Address: A “name” that uniquely identifies one
cell in the computer’s main memory. As shown in
Figure
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Measuring Memory Capacity
•Kilobyte = 1024 byte
•Megabyte = 1024 kilobyte
•Gigabyte = 1024 megabyte
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Mass Storage
•Due to the volatility and limited size of a
computer’s main memory, most computers have
additional memory devices called mass storage (or
secondary storage) system.
• example: magnetic disks, CDs, DVDs, magnetic
tapes, and flash drivers.
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Advantages Of Mass Storage
•less volatility
•large storage capacity
•low cost
•the ability to remove the storage medium from
machine for archival purpose
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Disadvantages Of Mass Storage
•It require mechanical motion and therefore require
significantly more time to store and retrieve data
than a machine’s main memory, where all activities
are performed electronically
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Mass Storage Systems
•Magnetic Systems
•Disk
•Tape
•Optical Systems
•CD
•DVD
•Flash Drives
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Magnetic Systems
•Example: magnetic disk
•Thin spinning disk with magnetic coating is used to
hold data.
•Read/write heads are placed above and/or below
the disk so that as the disk spins, each head
traverses a circle, called track.
•Be repositioning the read/write heads, different
concentric tracks can be accessed.
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Magnetic Systems
•Each track divided into small arcs called sectors on
which information is recorded as a continuous
string of bits.
•The location of tracks and sectors are marked
magnetically through the format process.
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Figure 1.9 A magnetic disk storage system
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Magnetic Systems
•Magnetic disk performance evaluation depends
on four criteria's:
•Seek time, the time required to move the
read/write head from track to another.
•Rotation delay (latency time), half -average
calculation the time required for the disk to
make complete rotation.
•Access time, the sum of the seek time and
rotation delay.
•Transfer rate, the rate at which data can be
transferred to/from the disk.
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Magnetic Tape
•An older from of mass storage
•Information is recorded on the magnetic coating of
a thin tape that is wound on a reel.
•Taps is mounted in a device called tape drive
(read/write).
•A major disadvantages of it, that moving between
different position on tape can be very timeconsuming
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Figure 1.10 Magnetic tape storage
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Optical System
•Another class of mass storage.
•CD, consists of reflective material covered with a
clear protective coating
•Information is recorded by creating variations in
their reflective surfaces
•Information retrieved by laser beam that monitors
irregularities on the reflective surface
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Digital Versatile Disks (DVD)
•Traditional CDs have capacity in range 600 to
700MB.
•Digital Versatile Disks (DVD), constructed from
multiple, semi-transparent layers that serves as
distinct surface when viewed by a precisely
focused laser.
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Flash Drivers
•In mass storage, data storage and retrieval is slow
compared to the speed of electronic circuitry .
•Flash memory has the potential of solving this
drawback.
•Bits are stored by sending electronic signals
directly to the storage medium
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File Storage
•File: A unit of data stored in mass storage system
•data stored in a mass storage system is
conceptually grouped into large unit called files
•Files stored on a magnetic disk must be
manipulated by sector.
•A block of data conforming to the specific
characteristics of a storage device is called a
physical record.
•A large file stored in a mass storage will consists
of many physical record. “the size of the sector”
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File Storage
•The nature f a file division is determined by the
information represented in the file.
•File containing information regarding a
company's employee would consists of multiple
units. Each consists of information about one
employee.
•These naturally producing “occurring” blocks of
data are called logical records.
•Logical record: the nature divisions within the
data
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File Storage
•Logical record consists of smaller units called
fields.
• Employee name, address, employee ID, etc.
•Identifying a field by a key field.
•Buffer: A memory area used for the temporary
storage of data (usually as a step in transferring the
data)
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Representing Text
•Each of different symbol on the text (alphabet
letter) is assigned a unique bit patterns
• the text is then representing as a long string of
bits.
•ASCII” American standard code for information
interchange”: Uses patterns of 7-bits to
represent most symbols used in written English
text.
•Today, it is extended to 8-bits.
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Figure 1.13 The message “Hello.” in ASCII
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Representing Text
•Unicode: Uses patterns of 16-bits to represent the
major symbols used in languages world side
•ISO standard: Uses patterns of 32-bits to represent
most symbols used in languages world wide
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Representing Numeric Values
•Binary notation is a way of representing numeric
values using only digits 0 and 1.
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Representing Numeric Values
•A number can be represented differently in
different systems. For example, the two numbers
(2A)16 and (52)8 both refer to the same quantity,
(42)10, but their representations are different.
•Each number system is associated with a base
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Representing Numeric Values
 A number represented as:
Integer
Fraction
 Each digit carries a certain weight based on its
position
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Binary system
•In the binary system, there are only two symbols
or possible digit values, 0 and 1. This base-2
system can be used to represent any quantity that
can be represented in decimal or other number
system
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Binary system
•For example, here is (11001)2 in binary
•(101.11)2
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Decimal
•The decimal system is composed of 10 numerals or
symbols. These 10 symbols are 0, 1, 2, 3, 4, 5, 6, 7,
8, and 9; using these symbols as digits of a
number, we can express any quantity.
•The decimal system, also called the base-10
system
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Decimal system
 (224)10
 Note that the digit 2 in position 1 has the value 20,
but the same digit in position 2 has the value 200
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Figure 1.15 The base ten and binary systems
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Figure 1.16 Decoding the binary representation 100101
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Exercise
•Convert each of the following binary
representation to its base ten:
•0101
•1001
•1011
•0110
•1000
•10010
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Figure 1.17 An algorithm for finding the binary representation
of a positive integer
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Figure 1.18 Applying the algorithm in Figure 1.15 to obtain the
binary representation of thirteen
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Binary addition
•To add two integers represented in binary
notation, we follow the same procedure in the
traditional base ten except that all sums are
computed using the following addition fact.
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Binary addition
111010
+ 11011
1
1
111010
+ 11011
01
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Binary addition
1
111010
+ 11011
0101
1
111010
+ 11011
010101
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Binary addition
111010
+ 11011
1010101
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Fraction in binary
•The digit to the right of radix point represent the
fractional part.
•The positions are assigned fractional quantities
•The first position is assigned the quantity ½
(which is 2-1), and so on
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Fraction in binary
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Decimal fraction to binary
•Covert 0.625 to base 2
625 x 2 = 1.25
.625 = .1
25 x 2 = 0.50
.625 = .10
.50 x 2 = 1.00
.625 = .101
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Representing images
•One mean of representing an image it to interpret
the image as a collection of dots, each is called
pixel.
•Pixel is a picture element.
•Each pixel is encoded.
•Image is represented as a collection encoded
pixels.
•Such collection is called bit map
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Black and white image
•Each pixel can be represented by a single bit.
•For more elaborate black and white picture, each
pixel can be represented by a collection of bits.
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Color Image
•RGB encoding
•Each pixel is represented as three color:
Red, Green and Blue.
•One byte is normally used to represent the
intensity of each color.
•Three byte of storage are required to represent a
single pixel.
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Representing Sounds
•The most generic method of encoding audio
information is to sample the amplitude of the
sound wave at regular intervals and record the
series of values obtained.
•Sound waves rises in amplitude, falls, rises at a
higher level, and then drop back to 0.
•The voice at one end of the communication is
encoded as numeric values representing the
amplitude of the voice.
•The numeric values can be then transmitted over
the communication line to the receiving end.
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Storing Integers
•Two’s complement Notation, excess notation are
used for representing integer values in computing
equipment.
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Two’s Complement Notation
•The most popular system within today’s computer.
•system in which negative numbers are represented
by the two's complement of the absolute value
•Used a fixed number of bits to represent each of
the values in the system.
•In today’s equipment, it is common to represent by
a pattern of 32 bits which allows a wide range of
numbers to be represented.
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Figure 1.21 Two’s complement notation systems
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Two’s Complement Notation
•The leftmost bit of a bit pattern represent the sign
of the value.
•“1” represent the negative sign.
•“0” represent the positive sign
•The complement of a pattern is the pattern
obtained by changing all the 0s to1s and all the 1s
to 0s.
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Coding The Value Using Two’s Complement
•Representing negative value
•Copy the original pattern from the right to left
until a 1 has been copied, then complement the
remaining bits until the final bit pattern.
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Example Of Encoding Value
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Addition In Two’s Complement
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Addition In Two’s Complement
•To add values represented in two’s complement,
we apply the same way that we used for binary.
•The answer must be in the same length, this
means that any extra bit generated at the left of
the answer by a final carry must be truncated.
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The Problem Of Overflow
•When using the two’s complement with pattern
with four bits, the largest positive integer that can
be represented is 7 and the most negative integer
is -8.
•We can’t obtain the correct answer to the problem
5+4.
•This is called overflow problem
•Overflow is the problem that occurs when a
computation produces a value that falls outside
the range of values that can be represented.
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Hexadecimal (Hex)
• Hex is a numbering system that uses Base 16. The
numbers 0-910 are represented normally, but the
numbers 1010 through 1510 are represented by
the letters A through F
• 1 hex digit is equivalent to 4 bits
• Numbers are 0,1,2…..8,9, A, B, C, D, E, F.
• The following shows that the number (2AE)16 in
hexadecimal is equivalent to 686 in decimal.
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Hexadecimal (Hex)
• The equivalent decimal number is N = 512 + 160 +
14 = 686.
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Hexadecimal (Hex)
•Using hexadecimal, a very large binary string of 1s
and 0s can be represented with just a few
hexadecimal numbers by breaking the binary
number into groups of four and then using the
hexadecimal equivalent; for example,
1101100101001111 can be written as 1101 1001
0100 1111
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Hexadecimal To Decimal
• The following shows how to convert the
hexadecimal number (1A)16 to decimal
= 1 × 161 + A × 160
=16 + 10 ×1
=16+10 = 26
convert (F4C)16 to decimal
= (F x 162) + (4 x 161) + (C x 160)
= (15 x 256) + (4 x 16) + (12 x 1)
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Decimal to hexadecimal
convert (4768)10 to hex.
= 4768 / 16 = 298
= 298 / 16 = 18
= 18 / 16 = 1
= 1 / 16 = 0
remainder 0
remainder 10 (A)
remainder 2
remainder 1
Answer: 1 2 A 0
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Hexadecimal To Binary
• (24C)16
• Each hexadecimal digit is converted to 4-bit
patterns
• 2 → 0010, 4 → 0100, and C → 1100
• (306 ) = (00110000 0110)
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Binary To Hexadecimal
Convert (010011100010)2 to hexadecimal ?
We first arrange the binary number in 4-bit
patterns:
0100 1110 0010
4
E 2
Convert (0010110001101011)2 to hexadecimal?
0010 1100 0110 1011
2
C
6
B
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Octal
•The Octal numbering system is similar to the
Hexadecimal numbering system.
•This big difference is that the maximum value for
Octal is 7 since it is Base 8
•1 octal digit is equivalent to 3 bits.
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Octal
• (1256)8
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Octal To Decimal
•convert (632)8 to decimal
= (6 x 82) + (3 x 81) + (2 x 80)
= (6 x 64) + (3 x 8) + (2 x 1)
= 384 + 24 + 2
= (410)10
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Decimal to Octal
•convert (177)10 to octal
177 / 8 = 22 remainder is 1
22 / 8 = 2 remainder is 6
2/8=0
remainder is 2
Answer = 2 6 1
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Binary To Octal
•111001112 = 3478
•11000 010101010 010 0012 = 30252218
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Octal To Binary
•convert (632)8 to binary
(110011010)2
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