Chapter 3
Computer Hard ware
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• A computer performs basically five
major operations :
1. it accepts data or instructions by any way
of input,
2. it stores data,
3. it can process data as required by the user,
4. it gives results in the form of output, and
5. it controls all operations inside a computer
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Computer Hardware
• Refers to the physical components
• Not one device but a system of many devices
• Major types of components include:
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Central Processing Unit
Main memory
Secondary storage devices
Input devices
Output devices
Slide 1- 3
Organization of a Computer System
Central
Processing
Unit
Input
Device
Main
Memory
Output
Device
Secondary
Storage
Slide 1- 4
The CPU
• Fetches instructions from main memory
• Carries out the operations commanded by the
instructions
• Each instruction produces some outcome
• A program is an entire sequence of instructions
• Instructions are stored as binary numbers
• Binary number - a sequence of 1’s and 0’s
Slide 1- 5
Main Memory
• Commonly known as random access memory,
or just RAM
• Holds instructions and data needed for
programs that are currently running
• RAM is usually a volatile type of memory
• Contents of RAM are lost when power is
turned off
Slide 1- 6
Secondary Storage
• A nonvolatile storage medium
• Contents retained while power is off
• Hard disk drives are most common
– Records data magnetically on a circular disk
– Provides fast access to large amounts of data
• Optical devices store data on CD’s as pits
• USB flash memory devices
– High capacity device plugs into USB port
– Portable, reliable, and fits easily in a pocket
Slide 1- 7
Input Devices
• Any type of device that provides data to a
computer from the outside world
• For example:
– Keyboard
– Mouse
– Scanner
Slide 1- 8
Output Devices
• Any type of device that provides data from a
computer to the outside world
• Examples of output data:
– A printed report
– An image such as a picture
– A sound
• Common output devices include:
– Monitor (display screen)
– Printer
Slide 1- 9
Knowing About: Computer Hardware
• Evolution of hardware
– 1950s: all hardware units were built using relays and vacuum tubes
– 1960s: introduction of transistors
– mid-1960s: introduction of integrated circuits (ICs)
– Present computers: use of microprocessors
• Bit: smallest and most basic data item in a computer; represents a 0 or a 1
• Byte: a grouping of eight bits
– E.g., 00010001
– What does this represent?
• Word: a grouping of one or more bytes
Slide 1- 10
(Low-Level) Languages
• Low-level languages
– First-generation and second-generation languages
– Machine-dependent languages
– The underlying representation the machine actually understands
• First-generation languages
– Also referred to as machine languages
– Consist of a sequence of instructions represented as binary
numbers
– E.g.: Code to ADD might be 1001 . To add 1+0 and then 1+1
our program might look like this:
• 1001 0001 0000
• 1001 0001 0001
Slide 1- 11
(Low-Level) Languages
• Second-generation languages
– Also referred to as assembly languages
– Abbreviated words are used to indicate operations
– Allow the use of decimal numbers and labels to indicate
the location of the data
• Assemblers
– Programs that translate assembly language programs into
machine language programs
– Our add program now looks like:
• ADD 1,0
• ADD 1,1
Assembler
1001
0001
0000
1001
0001
0001
Slide 1- 12
(High-Level) Languages
• High-level languages
– Third-generation and fourth-generation languages
– Programs can be translated to run on a variety of computer
types
• Third-generation languages
– Procedure-oriented languages
– Object-oriented languages
• Our Add program might now look like:
sum = value1 + value2
Compiler
1001
0001
0000
1001
0001
0001
Slide 1- 13
Third-Generation and FourthGeneration (High-Level) Languages
(Continued)
The Evolution of
Programming Languages
Slide 1- 14
Third-Generation and FourthGeneration (High-Level) Languages
• Procedure-oriented languages
– Programmers concentrate on the procedures used in
the program
– Procedure: a logically consistent set of instructions
which is used to produce one specific result
• Object-oriented languages
– Items are represented using self-contained objects
– Often used for graphical windows environments,
ability to re-use code efficiently
Slide 1- 15
1- Input units
• This units are used for the process of entering
data and programs in to the computer system.
• The input unit takes data from us to the
computer in an organized manner for
Processing.
• Examples of input units : Mouse, Modem,
Keyboard, Net card, Camera, microphone, CD,
DVD,HD
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2. Storage
• The process of saving data and instructions
permanently is known as storage.
• All data and instructions are stored before
and after processing
• Intermediate results of processing are also
stored here.
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CPU Components
• Two typical components of a CPU are:
• The arithmetic logic unit (ALU), which
performs arithmetic and logical operations.
• The control unit (CU), which extracts
instructions from memory and decodes and
executes them, calling on the ALU when
necessary.
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ALU
• The actual processing of the data and
instruction are performed by Arithmetic Logical
Unit
• The major operations performed by the ALU are
addition, subtraction, multiplication, division,
logic and comparison.
• Data is transferred to ALU from storage unit
when required
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Control Unit (CU)
• The Control Unit acts like the supervisor
• It extracts instructions from memory and decodes
and executes them, and sends the necessary signals
to the ALU to perform the operation needed.
• The control unit determines the sequence in which
computer programs and instructions are executed.
• Processing of programs stored in the main
memory, interpretation of the instructions and
issuing of signals for other units of the computer to
execute them.
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4- Output Units
This is the process of producing results from
the data for getting useful information.
The output is also stored inside the computer
for further processing.
Examples of output units: Screen, printers,
plotters, net card,..
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Physical computer components
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1. Central Processing Unit (CPU)
2. Computer Memory (RAM and ROM)
3. Data bus
4. Ports
5. Motherboard
6. Hard disk
7. Output Devices
8. Input Devices
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MEMORY
• There are two kinds of computer memory: primary
and secondary.
• Primary memory is accessible directly by the
processing unit.
• RAM (Random access memory) is an example of
primary memory
• As soon as the computer is switched off the contents
of RAM is lost.
• You can store and retrieve data much faster with
primary memory compared to secondary memory
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• Secondary memory such as floppy disks
,hard magnetic disk, etc., is located inside
and outside the computer.
• Primary memory is more expensive than
secondary memory.
• The size of primary memory is less than that
of secondary memory.
• Primary memory is faster than secondary
memory.
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Memory is used to store:
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i) instructions to execute a program and
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ii) data. When the computer is doing
any job, the data that have to be
processed are stored in the primary
memory. This data may come from an
input device like keyboard or from a
secondary storage device like a floppy
disk.
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Capacity of Primary Memory
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In computer’s memory both programs and data are
stored in the binary form
The binary system has only two values (bits ) 0
and 1.
Each of RAM’s locations stores one byte )8 bits)
(1 kilobyte is 1024 bytes)
(1Megabyte is 1024 kilobytes)
(1 terabyte is 1024 megabytes)
Thus 64 kilobyte (KB) memory is capable of
storing
64 X 1024 = 32,767 bytes
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• Each cell of memory contains one character
or 1 byte of data
• Primary storage is referred to as random
access memory (RAM) because it is
possible to randomly select and use any
location of the memory directly store and
retrieve data. It takes same time to any
address of the memory as the first address.
• It is also called read/write memory
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• The storage of data and instructions inside the
primary storage is temporary.
• It disappears from RAM as soon as the power
to the computer is switched off.
• The memories, which loose their content on
failure of power supply, are known as volatile
memories
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Read Only Memory (ROM)
• There is another memory in computer, which is
called Read Only Memory (ROM).
• The storage of program and data in the ROM is
permanent.
• The ROM stores some standard processing
programs supplied by the manufacturers to
operate the computer.
• The ROM can only be read by the CPU but it
cannot be changed.
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• The basic input/output program is stored
in the ROM that examines and initializes
various equipment attached to the PC
when the switch is made ON.
• The memories, which do not loose their
content on failure of power supply, are
known as non-volatile memories.
• ROM is non-volatile memory.
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PROM is another type of primary memory in
computer, which is called Programmable Read
Only Memory (PROM).
You know that it is not possible to modify or
erase programs stored in ROM, but it is possible
for you to store your program in PROM chip.
Once the programmes are written it cannot be
changed and remain intact even if power is
switched off.
Programs or instructions written in PROM or
ROM cannot be erased or changed.
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EPROM: Erasable Programmable Read Only
Memory, which over come the problem of
PROM & ROM.
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EPROM chip can be programmed time and
again by erasing the information stored earlier
in it.
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When the EPROM is in use information can
only be read.
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Cache Memory
• The speed of CPU is extremely high compared to
the access time of main memory.
• Therefore the performance of CPU decreases due to
the slow speed of main memory.
• Cache Memory is a small memory chip is attached
between CPU and Main memory whose access time
is very close to the processing speed of CPU.
• CACHE memories are accessed much faster than
conventional RAM. It is used to store programs or
data currently being executed or temporary data
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Registers:
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The CPU processes data and instructions with high
speed, there is also movement of data between
various units of computer.
It is necessary to transfer the processed data with
high speed.
So the computer uses a number of special memory
units called registers.
They are not part of the main memory but they
store data or information temporarily and pass it
on as directed by the control unit.
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auxiliary memory or secondary
storage
• 1-Hard Disk, in computer science, one or more
inflexible platters coated with material that allows
the magnetic recording of computer data.
• Hard disks provide faster access to data than
floppy disks and are capable of storing much
more information. Because platters are rigid, they
can be stacked so that one hard-disk drive can
access more than one platter.
• Most hard disks have from two to eight platters.
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• Magnetic Tape: Magnetic tapes are used for
large computers like mainframe computers
where large volume of data is stored for a
longer time
• Floppy Disk: It is similar to magnetic disk
discussed above. They are 5.25 inch or 3.5
inch in diameter. They come in single or
double density and recorded on one or both
surface of the diskette. The capacity of a 5.25inch floppy is 1.2 mega bytes whereas for 3.5
inch floppy it is 1.44 mega bytes.
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• floppy disk
* small magnetic data storage disk: a small
flexible magnetically coated disk in a rigid
plastic case on which data can be stored or
retrieved by a computer
* a regular floppy disk holds approximately
1.44 megabytes.
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CD- ROM
• CD-ROM, short for compact disc read-only memory,
a rigid plastic disk that stores a large amount of data
through the use of laser optics technology.
• Because they store data optically, CD-ROMs have a
much higher memory capacity than computer disks
that store data magnetically.
• However, CD-ROM drives, the devices used to
access information on CD-ROMs, can only read
information from the disc, not write to it.
• CD-ROMs can store large amounts of data and so are
popular for storing databases and multimedia
material. The most common format of CD-ROM
holds approximately 630 megabytes .
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INPUT OUTPUT DEVICES
• When you work with the computer you feed your
data and instructions through some devices to the
computer. These devices are called Input devices.
• Input Devices: Keyboard, Mouse, Scanner,
Optical Character Recognition (OCR)
• Output Devices
• Visual Display Unit: The most popular
input/output device is the Visual Display Unit
(VDU). It is also called the monitor
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• Terminals: It is a very popular interactive
input-output unit.
• It can be divided into two types: hard copy
terminals and soft copy terminals. A hard copy
terminal provides a printout on paper whereas
soft copy terminals provide visual copy on
monitor.
• A terminal when connected to a CPU sends
instructions directly to the computer.
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Printer
• It is an important output device which can
be used to get a printed copy of the
processed text or result on paper.
• There are different types of printers that are
designed for different types of applications.
• Depending on their speed and approach of
printing, printers are classified as impact and
non-impact printers.
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• Impact printers use the familiar typewriter
approach of hammering a typeface against the
paper and inked ribbon.
• Dot-matrix printers are of this type.
• Non-impact printers do not hit or impact a
ribbon to print.
• They use electro-static chemicals and ink-jet
technologies.
• Laser printers and Ink-jet printers are of this
type.
• This type of printers can produce color printing
and elaborate graphics.
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