Lecturer: Mr Chembe Christopher
Email: cchembe@mu.ac.zm
Student’s Email Group: ict131-2012@googlegroups.com
Course Content.
 Introduction to computer science;

Input and Output Devices;
  Memory;
  Software; and
  Hardware and Networking.
Lectures and Assessments
 3 hrs per week
 40 % Continuous Assessment
 10 % Quiz
 10 % Assignments
 20 % Test 0ne and two
 60 % Final Exam
Recommended Reading
 Data Processing Second Edition by H. M. Libati
 ICT 131 Module
 Lecture Resources
 Other Materials
Introduction
History of Computers
Types of Computers
Components of Computers
Introduction
A Computer is a device that accepts data in one form and processes it to produce
data in another form. The forms in which data is accepted or produced by the
computer vary enormously from simple words or numbers to signals sent from or
received by other items of technology. So, when the computer processes data it
actually performs a number of separate functions as follows:
 Input: The computer accepts data from outside for processing within.
 Storage: The computer holds data internally before, during and after
processing.
 Processing: The computer performs operations on the data it holds within.
 Output: The computer produces data from within for external use.
Data
process
Input
Data
Output
Storage
History of Computing
The first electronic computers were produced in the
1940s. since then a series of radical breakthroughs in
electronic occurred. With major breakthrough the
computer based upon the older form of electronics have
been replaced by a new “generation” of computers based
upon the newer form of electronics. These “generations”
classified as follows:
 First generation
 Second generation
 Third generation
 Fourth generation
 Fifth generation
First Generation
 1946-1956
 Vacuum tubes to store and process information.
 Vacuum tubes consumed large amounts of power,
generated heat, and were short-lived.
 Limited memory and processing capability.
 Examples of first generation computers are EDSAC,
EDVAC, LEO and UNIVAC1.
EDSAC
EDSAC
Second Generation
 1957-1963
 Transistors for storage and processing information.
 Transistors consumed less power than vacuum tubes,
produced less heat, and were cheaper, more stable, more
reliable.
 Second generation computers, with increased processing
and storage capabilities, began to be more widely used for
scientific and business purposes.
 Examples of second generation computers are LEO mark
III, ATLAS and the IBM 7000 series.
Third Generation
 1964- 1979
 Integrated circuits(IC) for storing and processing
information.
 Integrated circuits are made by printing numerous,
small transistors on silicon chips. These devices are
called semiconductors.
 Third generation computers employed software that
could be used by non-technical people, thus enlarging
the computers role in business.
 Examples of third generation computers are the ICL
1900 series and the IBM 360 series.
Fourth Generation
 1980-present,
 Very Large Scale Integrated circuits (VLSI) to store and
process information.
 The VLSI technique allows the installation of hundreds of
thousands of circuits (transistors and other components)
on a small chip.
 With ultra large-scale integration, 10 million transistors
could be placed on a chip.
 These computers are inexpensive and widely used in
business and everyday life.
Fifth Generation
 The first four generations of computer hardware are based on the
Von Neumann architecture, which processed information
sequentially, one instruction at a time.
 The fifth generation of computers uses massively parallel processing
to process multiple instructions simultaneously.
 Massively parallel computers use flexibly connected networks
linking thousands of inexpensive, commonly used chips to address
large computing problems, attaining supercomputer speeds.
 With enough chips networked together, massively parallel machines
can perform more than a trillion floating point operations per seconda teraflop. A floating point operation (flop) is a basic computer
arithmetic operation, such as addition or subtraction, on numbers that
include a decimal point.
Types of Computers
 Computers are distinguished on the basis of their
processing capabilities. Computers with the most
processing power are also the largest and most expensive.
 Super Computers
 Mainframes
 Minicomputers
 Personal Computers
 Network Computers
Super Computers
 Super computers are the computers with the most processing power.
 Super computers are especially valuable for large simulation models
of real-world phenomena
 Super computers are used to model the weather for better weather
prediction, to test weapons non-destructively, to design aircraft, for
more efficient and less costly production, and to make sequences in
motion pictures.
 Super computers are generally operated at 4 to 10 times faster than
the next most powerful computer class, the mainframe.
 Super computers use the technology of parallel processing. However,
in contrast with neural computing, which uses massively parallel
processing, super-computers use noninterconnected CPUs.
Mainframes
 Mainframes are not as powerful and generally not as expensive
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as supercomputers.
Large corporations, where data processing is centralized
Applications that run on a mainframe can be large and
complex, allowing for data and information to be shared
throughout the organization.
Online secondary storage may use high-capacity magnetic and
optical storage media with capacities in the gigabyte to terabyte
range.
Several hundreds or even thousands of online computers can be
linked to a mainframe.
Minicomputers
 Minicomputers are also called midrange computers, are
smaller and less expensive than mainframe computers.
 Minicomputers are usually designed to accomplish
specific tasks such as process control, scientific research,
and engineering applications.
 Larger companies gain greater corporate flexibility by
distributing data processing with minicomputers in
organizational units instead of centralizing computing at
one location.
 These minicomputers are connected to each other and
often to a mainframe through telecommunication links.
Personal Computers
 Personal computers are the smallest and least expensive
category of general purpose computers.
 In general, modern personal computers have between 2 to 4
gigabytes of primary storage, a CD-ROM drive, and 250 to 350
gigabytes or more of secondary storage.
 They may be subdivided into four classifications based on size:
 Desktops
 Laptops
 Notebooks
 Palmtops
Network Computers
 The computers described so far are considered “smart”
computers. However, mainframe and midrange computers
use “dumb” terminals, which are basically input/output
devices.
 A network computer (NC) is a desktop terminal that does
not store software programs or data permanently. Similar to
a “dumb” terminal, the NC is simpler and cheaper than a
PC and easy to maintain.
 Users can download software or data they need from a
server or a mainframe over an intranet or internet. There is
no need for hard disks, floppy disks, CD-ROMs and their
drives. The central computer can save any material for the
user. The NCs provide security as well. However, users are
limited in what they can do the terminals.
Components of a Computer
 Computer hardware is composed
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of the following
components:
The input devices accept data and instructions and
convert them to a form that the computer can understand.
The output devices present data in a form people can
understand.
The CPU manipulates the data and controls the tasks done
by the other components.
The primary storage (internal storage) temporarily stores
data and program instructions during processing. It also
stores intermediate results of the processing.
The secondary storage (external) stores data and
programs for future use.
Components of a Computer cont’d
Input/Output Devices
 The input/output (I/O) devices of a computer are not part of the
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CPU, but are channels for communicating between the external
environment and the CPU.
Data and instructions are entered into the computer through
input devices, and processing results are provided through
output devices.
Widely used I/O devices are the visual display unit (VDU),
storage, printers, keyboards, mouse and image-scanning devices.
I/O devices are controlled directly by the CPU or indirectly
through special processors dedicated to input and output
processing.
Generally speaking, I/O devices are subclassified into secondary
storage devices (primarily disk and tape drives) and peripheral
devices (any input/output device that is attached to the
computer).
Central Processing Unit(CPU)
 The central processing unit (CPU) is also referred to as
a microprocessor because of its small size.
 The CPU is the center of all computer-processing
activities, where all processing is controlled, data are
manipulated, arithmetic computations are performed,
and logical comparisons are made.
 The CPU consists of the control unit, the arithmeticlogic unit (ALU), and the primary storage (or main
memory).
Arithmetic and Logic Unit(ALU)
 The arithmetic-logic unit performs required
arithmetic and comparisons, or logic, operations.
 The ALU adds, subtracts, multiplies, divides,
compares, and determines whether a number is
positive, negative, or zero.
 All computer applications are achieved through these
six operations.
 The ALU operations are performed sequentially, based
on instructions from the control unit.
Primary Storage
Primary storage, or main memory, stores data and program
statements for the CPU. It has four basic purposes:
 1. To store data that have been input until they are
transferred to the ALU for processing
 2. To store data and results during intermediate stages of
processing
 3. To hold data after processing until they are transferred
to an output device
 4. To hold program statements or instructions received
from input devices and from secondary storage
Control Unit
 The control unit reads instructions and directs the other components of the
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computer system to perform the functions required by the program.
It interprets and carries out instructions contained in computer programs,
selecting program statements from the primary storage, moving them to the
instruction registers in the control unit, and then carrying them out.
The control unit does not actually change or create data; it merely directs
the data flow within the CPU.
The control unit can process only one instruction at a time, but it can
execute instructions so quickly (millions per second)
The series of operations required to process a single machine instruction is
called a machine cycle. Each machine cycle consists of the instruction
cycle, which sets up circuitry to perform a required operation, and the
execution cycle, during which the operation is actually carried out.
Buses
 Instructions and data move between computer subsystems and the
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processor via communications channels called buses.
A bus is a channel (or shared data path) through which data are
passed in electronic form. Three types of buses link the CPU,
primary storage, and the other devices in the computer system.
The data bus moves data to and from primary storage.
The address bus transmits signals for locating a given address in
primary storage.
The control bus transmits signals specifying whether to “read” or
“write” data to or from a given primary storage address, input device,
or output device.
The capacity of a bus, called bus width, is defined by the number of
bits they carry at one time. Bus speeds are also important, currently
averaging about 133 megahertz (MHz).
Processor Speed
 The speed of a chip depends on four things: the clock speed, the
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word length, the data bus width, and the design of the chip.
The clock, located within the control unit, is the component that
provides the timing for all processor operations. The beat
frequency of the clock (measured in megahertz [MHz] or
millions of cycles per second) determines how many times per
second the processor performs operations.
Word length is the number of bits( detail of bits you will be
studying in unit-5) that can be processed at one time by a chip.
Chips are commonly labelled as 8-bit, 16-bit, 32-bit, 64-bit, and
128-bit devices.
The larger the word length, the faster the chip speed. The width
of the buses determines how much data can be moved at one
time. The wider the data bus (e.g., 64 bits), the faster the chip.
Input Devices
Output Devices
Input Devices
 Users can command the computer and communicate with
it by using one or more input devices. Each input device
accepts a specific form of data.
 For example, keyboards transmit typed characters, and
handwriting recognizers “read” handwritten characters.
 Users want communication with computers to be simple,
fast, and error free. Therefore, a variety of input devices
fits the needs of different individuals and applications
 Categories
Keying devices
Examples
Punched card reader
Keyboard
Point-of-sale terminal
Pointing devices
(Devices that point to objects
on the computer screen)
Mouse
Touch screen
Touchpad (or track pad)
Light pen
Joysticks
Optical character recognition
(Devices that scan characters)
Bar code scanner
Optical character reader
Optical mark reader
Wand reader
Cordless reader
Handwriting recognizers
Pen
Voice recognizers
(Data are entered by voice)
Other devices
Microphone
MICR
ATM
Digitizers
Keyboard:
The most common input device is the keyboard. The
keyboard is designed like a typewriter but with many
additional special keys.
Mouse:
The computer mouse is a handheld device used to
point a cursor at a desired place on the screen, such as
an icon, a cell in a table, an item in a menu, or any
other object.
Once the arrow is placed on an object, the user clicks a
button on the mouse, instructing the computer to take
some action.
Punched card reader:
A card reader such as the IBM 3505 is an electronically
mechanized input device used to read Hollerith Cards.
Sometimes combined with card punches such as the
IBM 2540 card reader-punch, such devices were almost
always attached to a computer but in earlier days could
be found as stand-alone duplication or serialization
devices.
Joystick:
Joysticks are used primarily at workstations that can
display dynamic graphics. They are also used in
playing video games. The joystick moves and positions
the cursor at the desired object on the screen.
Automated Teller Machine:
Automated teller machines (ATMs) are interactive
input/output devices that enable people to obtain
cash, make deposits, transfer funds, and update their
bank accounts instantly from many locations. ATMs
can handle a variety of banking transactions, including
the transfer of funds to specified accounts. One
drawback of ATMs is their vulnerability to computer
crimes and to attacks made on customers as they use
outdoor ATMs.
 Point-of-Sale Terminals:
Many retail organizations utilize point of sale (POS) terminals.
The POS terminal has a specialized keyboard. POS devices
increase the speed of data entry and reduce the chance of
errors. POS terminals may include many features such as
scanner, printer, voice synthesis and accounting software.
 Bar Code Scanner
Bar code scanners scan the black-and-white bars written in the
Universal Product Code (UPC). This code specifies the name
of the product and its manufacturer (product ID). Then a
computer finds in the database the price equivalent to the
product’s ID. Bar codes are especially valuable in high volume
processing where keyboard energy is too slow and/or
inaccurate.
 Optical Character Reader
With an optical character reader (OCR), source
documents such as reports, typed manuscripts, and
books can be entered directly into a computer without
the need for keying. An OCR converts text and images
on paper into digital form and stores the data on disk
or other storage media. OCRs are available in different
sizes and for different types of applications.
 Magnetic Ink Character Reader:
Magnetic ink character readers (MICRs) read
information printed on checks in magnetic ink. This
information identifies the bank and the account
number. On a canceled check, the amount is also
readable after it is added in magnetic ink.
Output Devices
 The output generated by a computer can be transmitted to
the user via several devices and media. The presentation
of information is extremely important in encouraging
users to embrace computers.
 Monitors
The data entered into a computer can be visible on the
computer monitor, which is basically a video screen that
displays both input and output. Monitors come in different
sizes, ranging from inches to several feet, and in different
colors. The major benefit is the interactive nature of the
device.
 Impact Printers:
Like typewriters, impact printers use some
form of striking action to press a carbon or
fabric ribbon against paper to create a
character.
The most common impact printers are the dot
matrix, daisy wheel, and line.
Line printers print one line at a time; therefore,
they are faster than one-character type printers.
Impact printers are slow and noisy, cannot do
high-resolution graphics, and are often subject
to mechanical breakdowns.
 Nonimpact Printers:
Nonimpact printers overcome the deficiencies
of impact printers.
Laser printers are of higher speed, containing
high-quality devices that use laser beams to
write information on photosensitive drums,
whole pages at a time; then the paper passes
over the drum and picks up the image with
toner.
 Thermal printers create whole characters on
specially treated paper that responds to
patterns of heat produced by the printer.
 Ink-jet printers shoot tiny dots of ink onto
paper. Sometimes called bubble jet, they are
relatively inexpensive and are especially
suited for low-volume graphical applications
when different colors of ink are required.
 Plotters
Plotters are printing devices using
computer-driven pens for creating highquality black-and-white or color graphic
images—charts, graphs, and drawings.
They are used in complex, low-volume
situations such as engineering and
architectural drawing, and they come in
different types and sizes.
Main Memory
Secondary Storage Memory
In computing and telecommunications a bit is a basic
unit of information storage and communication;
it is the maximum amount of information that can be
stored by a device or other physical system that can
normally exist in only two distinct states.
These states are often interpreted (especially in the
storage of numerical data) as the binary digits 0 and 1.
They may be interpreted also as logical values, either
"true" or "false"; or two settings of a flag or switch,
either "on" or "off".
Byte
A byte is an ordered collection of bits, with each bit
denoting a single binary value of 1 or 0.
The byte most often consists of 8 bits in modern
systems;
however, the size of a byte can vary and is generally
determined by the underlying computer operating
system or hardware.
Byte cont’d
 Historically, byte size was determined by the number
of bits required to represent a single character from a
Western character set.
 Its size was generally determined by the number of
possible characters in the supported character set and
was chosen to be a divisor of the computer's word size.
Word
 A group of bytes is called a word.
 Word size dependent on the architecture platform(eg.,
32-bit machine, 64-bit machine).
 A 32-bit word contains 4 bytes; a 64-bit word contains
8 bytes. In a 32-bit machine, everything will be 32-bits
wide (all registers, buses, numbers).
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The wider the word, the higher the processing power.
Memory
 There are two categories of memory: the register,
which is part of the CPU and is very fast, and the
internal memory chips, which reside outside the
CPU and are slower.
 A register is circuitry in the CPU that allows for the
fast storage and retrieval of data and instructions
during the processing.
 The internal memory comprises two types of
storage space: RAM and ROM and
 is used to store data just before they are processed by
the CPU.
Random Access Memory(RAM)
 RAM is the place in which the CPU stores the
instructions and data it is processing.
 The larger the memory area, the larger the programs
that can be stored and executed.
 With the newer computer operating system software,
more than one program may be operating at a time,
each occupying a portion of RAM.
 Most personal computers as of 2010 needed 3 to 4
gigabytes of RAM to process “multimedia”
applications, which combine sound, graphics,
animation, and video, thus requiring more memory.
RAM – Cont’d
 The advantage of RAM is that it is very fast in storing
and retrieving any type of data, whether textual,
graphical, sound, or animation-based.
 Its disadvantages are that it is relatively expensive and
volatile. This volatility means that all data and
programs stored in RAM are lost when the power is
turned off.
 To lessen this potential loss of data, many of the newer
application programs perform periodic automatic
“saves” of the data.
RAM – Cont’d
 Many software programs are larger than the internal,
primary storage (RAM) available to store them. To get
around this limitation, some programs are divided into
smaller blocks, with each block loaded into RAM only
when necessary.
 However, depending on the program, continuously loading
and unloading blocks can slow down performance
considerably, especially since secondary storage is so much
slower than RAM. As a compromise, some architectures use
high-speed cache memory as a temporary storage for the
most frequently used blocks.
Types of RAM
 Dynamic random access memories (DRAM) are
the most widely used RAM chips. These are known to
be volatile since they need to be recharged and
refreshed hundreds of times per second in order to
retain the information stored in them.
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 Synchronous DRAM (SDRAM) is a relatively new
and different kind of RAM.
 SDRAM is rapidly becoming the new memory
standard for modern PCs.
 The reason is that its synchronized design permits
support for the much higher bus speeds that have
started to enter the market.
 Static Random Access Memory (SRAM):
Random-access memory in which each bit of storage
is a bistable, commonly consisting of cross-coupled
inverters.
It is called "static" because it will retain a value as long
as power is supplied, unlike dynamic random-access
memory (DRAM) which must be regularly refreshed.
It is however, still volatile, i.e. it will lose its contents
when the power is switched off, in contrast to ROM.
 SRAM is usually faster than DRAM but since each
bit requires several transistors (about six) you can
get less bits of SRAM in the same area.
 It usually costs more per bit than DRAM and so is
used for the most speed-critical parts of a
computer (e.g. cache memory) or other circuit.
Read Only Memory(ROM)
 ROM is that portion of primary storage that cannot be
changed or erased. ROM is nonvolatile; that is, the
program instructions are continually retained within
the ROM, whether power is supplied to the computer
or not.
 ROM is necessary to users who need to be able to
restore a program or data after the computer has been
turned off or, as a safeguard, to prevent a program or
data from being changed. For example, the
instructions needed to start, or “boot,” a computer
must not be lost when it is turned off.
Types of ROM
 Programmable read-only memory (PROM) is a
memory chip on which a program can be stored. But
once the PROM has been used, you cannot wipe it
clean and use it to store something else. Like ROMs,
PROMs are nonvolatile.
 Erasable programmable read-only memory
(EPROM) is a special type of PROM that can be erased
by exposing it to ultraviolet light.
Stored Program Concept
 A stored-program digital computer is one that keeps its
programmed instructions, as well as its data, in read-write,
random-access memory (RAM).
 Stored-program computers were advancement over the
program-controlled computers of the 1940s, such as the
colossus and the ENIAC, which were programmed by
setting switches and inserting patch leads to route data and
to control signals between various functional units.
 In the vast majority of modern computers, the same
memory is used for both data and program instructions.
Secondary Storage
 Secondary storage is separate from primary storage
and the CPU, but directly connected to it. An example
would be the 3.5-inch disk you place in your PC’s A
drive.
 It stores the data in a format that is compatible with
data stored in primary storage, but secondary storage
provides the computer with vastly increased space for
storing and processing large quantities of software and
data.
 Primary storage is volatile, contained in memory
chips, and very fast in storing and retrieving data.
Secondary Storage cont’d
 In contrast, secondary storage is nonvolatile, uses
many different forms of media that are less expensive
than primary storage, and is relatively slower than
primary storage.
 Secondary storage media include
 magnetic tape,
 magnetic disk,
 magnetic diskette,
 optical storage,
 and digital videodisk.
Magnetic Tape
 Magnetic Tape is kept on a large reel or in a small
cartridge or cassette. Today, cartridges and
cassettes are replacing reels because they are easier
to use and access.
 The principal advantages of magnetic tapes are
that it is inexpensive, relatively stable, and long
lasting, and that it can store very large volumes of
data.
Magnetic Tape cont’d
 A magnetic tape is excellent for backup or archival
storage of data and can be reused.
 The main disadvantage of magnetic tape is that it
must be searched from the beginning to find the
desired data.
 The magnetic tape itself is fragile and must be
handled with care. Magnetic tape is also labour
intensive to mount and dismount in a mainframe
computer.
Magnetic Drums
 Drum memory is a magnetic data storage device and
was an early form of computer memory widely used in
the 1950s and into the 1960s
 For many machines, a drum formed the main working
memory of the machine, with data and programs
being loaded on to or off the drum using media such
as paper tape or punch cards.
 Drums were so commonly used for the main working
memory that these computers were often referred to as
drum machines.
Magnetic Drums cont’d
 Drums were later replaced as the main working
memory by memory such as core memory and a
variety of other systems which were faster as they had
no moving parts, and which lasted until
semiconductor memory entered the scene.
 A drum is a large metal cylinder that is coated on the
outside surface with a ferromagnetic recording
material.
 A row of read-write heads runs along the long axis of
the drum, one for each track.
Magnetic Disk
 Magnetic disks, also called hard disks, alleviate
some of the problems associated with magnetic
tape by assigning specific address locations for
data,
 so that users can go directly to the address without
having to go through intervening locations looking
for the right data to retrieve. This process is called
direct access.
Magnetic Disk cont’d
 Most computers today rely on hard disks for
retrieving and storing large amounts of
instructions and data in a non-volatile and rapid
manner.
 The hard drives of 2010 microcomputers provide
250 to 350 gigabytes of data storage.
 The speed of access to data on hard-disk drives is a
function of the rotational speed of the disk and the
speed of the read/write heads. The read/write heads
must position themselves, and the disk pack must
rotate until the proper information is located.
Advanced disk drives have access speeds of 8 to 12
milliseconds.
 Magnetic disks provide storage for large amounts of
data and instructions that can be rapidly accessed.
Another advantage of disks over reel is that a robot can
change them. This can drastically reduce the expenses
of a data center.
 The disks’ disadvantages are that they are more
expensive than magnetic tape and they are susceptible
to “disk crashes.”
 In contrast to large, fixed disk drives, one current
approach is to combine a large number of small disk
drives each with 10- to 50-gigabyte capacity,
developed originally for microcomputers.
 These devices are called redundant arrays of
inexpensive disks (RAID). Because data are stored
redundantly across many drives, the overall impact
on system performance is lessened when one drive
malfunctions. Also, multiple drives provide multiple
data paths, improving performance. Finally, because
of manufacturing efficiencies of small drives, the
cost of RAID devices is significantly lower than the
cost of large disk drives of the same capacity.
Magnetic Diskette
 Hard disks are not practical for transporting data of
instructions from one personal computer to another.
To accomplish this task effectively, developers created
the magnetic diskette.
 (These diskettes are also called “floppy disks,” a name
first given the very flexible 5.25-inch disks used in the
1980s and early 1990s.)
Magnetic Diskette cont’d
 The magnetic diskette used today is a 3.5-inch,
removable, somewhat flexible magnetic platter
encased in a plastic housing.
 Unlike the hard disk drive, the read/write head of the
diskette drive actually touches the surface of the disk.
As a result, the speed of the drive is much slower, with
an accompanying reduction in data transfer rate.
Magnetic Diskette cont’d
 However, the diskettes themselves are very
inexpensive, thin enough to be mailed, and able to
store relatively large amounts of data.
 A standard high-density disk contains 1.44 megabytes.
 Zip disks are larger than conventional floppy disks,
and about twice as thick. Disks formatted for zip drives
contain 250 megabytes.
Optical Storage
 Optical storage devices have extremely high storage
density. Typically, much more information can be
stored on a standard 5.25-inch optical disk than on a
comparably sized floppy (about 400 times more).
Since a highly focused laser beam is used to read/write
information encoded on an optical disk, the
information can be highly condensed.
 Another advantage of optical storage is that the
medium itself is less susceptible to contamination or
deterioration.
Digital Video Disk(DVD)
 DVD is a new storage disk that offers higher quality
and denser storage capabilities.
 In 2001, the disk’s maximum storage capacity is 17
Gbytes, which is sufficient for storing about five
movies.
 It includes superb audio (six-track vs. the two-track
stereo).
 Like CDs, DVD comes as DVD-ROM (read-only) and
DVD-RAM. Rewritable DVD-RAM systems are already
on the market, offering a capacity of 4.7 GB
Flash Memory
 Flash memory is a non-volatile computer memory
that can be electrically erased and reprogrammed. It is
a technology that is primarily used in memory cards
and USB flash drives for general storage and transfer of
data between computers and other digital products.
 It is a specific type of EEPROM (Electrically Erasable
Programmable Read-Only Memory) that is erased and
programmed in large blocks; in early flash the entire
chip had to be erased at once.
Software
Operating Systems
Overview of Programming Languages
System Development Methodology
Software
 Software is a term used (in contrast to hardware) to
describe all programs that are used in a particular
computer installation. The term is often used to mean
not only the program themselves but they are
associated documentation.
 Computer hardware cannot perform a single act
without instructions. These instructions are known as
software or computer programs.
 Software is at the heart of all computer applications.
 There are two major types of software: application
software and system software.
System Software
 Systems software acts primarily as an intermediary
between computer hardware and application
programs, and knowledgeable users may also directly
manipulate it.
 Systems software provides important self-regulatory
functions for computer systems, such as loading itself
when the computer is first turned on, as in Windows
Professional; managing hardware resources such as
secondary storage for all applications; and providing
commonly used sets of instructions for all applications
to use.
System Software – Cont’d
 There are subdivision in system software
 Operating systems and control programs
 Translators
 Utilities and service programs
 Database Management System
Operating Systems and Control
Programs
 Computers are required to give efficient and relative service
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without the need for continual intervention by the user.
On smaller computer systems, such as micro computers, the
control program may also accept commands typed in by the user.
Such a control program is often called monitor
On larger computer systems it is common for only part of the
monitor to remain in main storage. Other parts of the monitor
are brought into memory when required, ie, there are “resident”
and “transient” parts of the monitor.
The resident part of the monitor on large systems is often called
the Kernel, Executive or supervisor program.
An operating system is a suite of programs that takes over the
operation of the computer to the extent of being able to allow a
number of programs to be run on the computer without human
intervention by an operator.
Translators
 The earliest computer programs were written in the
actual language of the computer. Nowadays, however,
programmers write their programs in programming
languages which relatively easy to learn.
 Each program is translated into the language of the
machine before being used for operational purposes.
This translation is done by computer programs called
translators.
Utilities and service programs
 Utilities, also called service programs, are system
programs that provide a useful service to the user of
the computer by providing facilities for performing
tasks of a routine nature.
 Common types of utility programs are:
 Sort
 Editor
 File Copying
 Dump
 File Maintenance
 Tracing and Debugging
Database Management System
 The database management system is a complex software
system that constructs, expands and maintains the
database. It also provides the controlled interface between
the user and data in the database.
 The DBMS allocates storage to data. It maintains indices so
that any required data can be retrieved, and so that
separate items of data in the database can be crossreferenced.
 The structure of a database is dynamic and can be changed
as needed. The DBMS provides an interface with user
programs. These may be written in number of different
programming languages.
Operating Systems
 An operating system, or OS, is a software program that
enables the computer hardware to communicate and
operate with the computer software.
 An OS is responsible for the management and
coordination of activities and the sharing of the
resources of the computer.
 The operating system acts as a host for computing
applications run on the machine. As a host, one of the
purposes of an operating system is to handle the
details of the operation of the hardware.
Functions of the OS
 Processor management - that is, assignment of processor to different tasks
being performed by the computer system.
 Memory management - that is, allocation of main memory and other storage
areas to the system programmes as well as user programmes and data.
 Input/output management - that is, co-ordination and assignment of the
different output and input device while one or more programmes are being
executed.
 File management - that is, the storage of file of various storage devices to
another. It also allows all files to be easily changed and modified through the
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use of text editors or some other files manipulation routines.
Establishment and enforcement of a priority system - that is, it determines
and maintains the order in which jobs are to be executed in the computer
system.
Automatic transition from job to job as directed by special control statements.
Interpretation of commands and instructions.
Coordination and assignment of compilers, assemblers, utility programs, and
other software to the various user of the computer system.
Facilitates easy communication between the computer system and the
computer operator (human). It also establishes data security and integrity.
Types of Operating Systems
 Single-program systems
 Simple batch system
 Multi-access and Time-sharing systems
 Real-time systems
Application Software
 Application software is a set of computer instructions,
written in a programming language.
 The instructions direct computer hardware to perform
specific data or information processing activities that
provide functionality to the user.
 This functionality may be broad, such as general word
processing, or narrow, such as an organization’s payroll
program.
 An application program applies a computer to a need,
such as increasing productivity of accountants or improved
decisions regarding an inventory level. Application
programming is either the creation or the modification
and improvement of application software.
Programming Languages
 Programming languages are the basic building blocks
for all systems and application software.
 Programming languages are basically a set of symbols
and rules used to write program code. Each language
uses a different set of rules and the syntax that dictates
how the symbols are arranged so they have meaning.
 The characteristics of the languages depend on their
purpose.
 Languages also differ according to when they were
developed; today’s languages are more sophisticated
than those written in the 1950s and the 1960s.
Levels of Programming languages
 We can choose any language for writing a program
according to the need. But a computer executes
programs only after they are represented internally in
binary form (sequences of 1’s and 0's).
 Programs written in any other language must be
translated to the binary representation of the
instructions before they can be executed by the
computer.
 Programs written for a computer may be in one of the
following categories of languages.
Machine Language
 This is a sequence of instructions written in the form of
binary numbers consisting of 1's, 0's to which the computer
responds directly. 'machine language was initially referred
to as code, although now the term code is used more
broadly to refer to any program text.
 An instruction prepared in any machine language will have
at least two parts. The first part is the Command or
Operation, which tells the computer what functions is to be
performed. All computers have an operation code for each
of its functions. The second part of the instruction is the
operand or it tells the computer where to find or store the
data that has to be manipulated.
Assembly Language
 When we employ symbols (letter, digits or special
characters) for the operation part, the address part and
other parts of the instruction code, this representation is
called an assembly language program. This is considered to
be the second generation language.
 Machine and Assembly languages are referred to as low
level languages since the coding for a problem is at the
individual instruction level.
 Each machine has got its own assembly language which is
dependent upon the internal architecture of the processor.
An assembler is a translator which takes its input in the
form of an assembly language program and produces
machine language code as its output.
High-level Language
 The time and cost of creating machine and assembly languages was
quite high. And this was the prime motivation for the development of
high level languages.
 Since a high level source program must be translated first into a form
the machine can understand, this is done by software called Compiler
which takes the source code as input and produces as output the
machine language code of the machine on which it is to be executed.
 During the process of translation, - the Compiler reads the source
programs statement-wise and checks the syntactical errors. If there is
any error, the computer generates a print-out of the errors it has
detected. This action is known as diagnostics.
 There is another type of software which also does the translation. This
is called an Interpreter. The Compiler and Interpreter have different
approaches to translation. The following table lists the differences
between a Compiler and an Interpreter.
System Development Methodology
 New computer systems frequently replace existing manual
systems, and the new systems may themselves be replaced
after sometime.
 The process of replacing the old system by the new is often
organized into a series of stages. The whole process is
called “system life cycle”.
 The system life cycle may be regarded as a “framework”
upon which the work can be organized and methods
applied.
 The system life cycle is the traditional framework for
developing new systems.
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 Preliminary survey or study
The purpose of this survey is to establish whether there is
need for a new system and if so to specify the objectives of
the system.
 Feasibility study
The purpose of the feasibility study is to investigate the
project in sufficient depth to be able to provide information
that either justifies the development of the new system or
shows why the project should not continue.
 Investigation and fact recording
At this stage in the life cycle a detailed study is conducted.
The purpose of this study is to fully understand the existing
system and to identify the basic information requirements.
This requires a contribution from the users of both of the
existing system and the proposed system.
 Analysis
Analysis of the full description of the existing system and of the
objectives of the proposed system should lead to the full specification
of users’ requirements.
 Design
The analysis may lead to a number of possible alternative designs. For
example, different combinations of manual and computerized
elements may be considered. Once one alternative has been selected
the purpose of the design stage is to work from the requirements
specification to produce a system specification.
 Implementation
Implementation involves following the details set out in the system
specification. Three particularly important tasks are hardware
provision, programming and staff training. It is worth observing in
passing that the programming task has its own “life cycle” in the form
of the various stages in programming, such that analysis and design
occur at many different levels.
 Maintenance and review
Once a system is implemented and in full operation it is examined to
see if it has met the objectives set out in the original specification.
Hardware and Networking