Computer system

1. Chapter Two
Computer System
 Recall from your previous studies that you know
systems like Digestive system, Circulatory system
and so on. What similarity can you understand from
these systems? For example digestive system is
composed of a group of components like mouth,
stomach, intestine and so on.
 Likewise, a computer system is also composed of
physical components (hardware) and non-physical
component (software) that work together in
coordination to achieve a common goal (data
processing).
 In general, a system is a group of components that

2. Components of Computer System
 Computer system is a system that has two
fundamental components: Hardware component and
Software component.
 The primary purpose of computer systems in most
businesses today is to transform data into
information that can be used by people to make
decisions.
 Hardware is the physical component of the computer
system that we can see, touch and sense. It includes
devices the computer system use to interact with the
external world, to process the data it has received, to
store the data it has received and processed.
 Software, on the other hand, is the set of instructions
that tell the hardware how to perform a task. Without
software, the hardware is useless.

3. Hardware Component
Input devices
 The function of input devices is to accept data and convert it into a form suitable for computer
processing. It may include: keyboard, mouse, scanner and so on.
1. Keyboard
 A computer keyboard is a peripheral modeled after the typewriter keyboard. Keyboards are
designed for the input of text and characters and also to control the operation of a computer.
The keys on the keyboard are grouped according to their functions as follows:
Alphanumeric keys
 The group of keys that comprises the alphabets, punctuation marks, and digits. These keys are
used to enter text, digit, and punctuation marks.
Function keys
 The group of keys found at the top of keyboard labeled from F1 to F12. These keys execute
different commands based on the applications that are running.
Numeric keypad
 Found at the right most of the keyboard, is the numeric keypad. These keys work with the
special key called NumLock – located at the left-top corner of the numeric keypad. when
NumLock is on, the numeric keypad is used to enter digits and arithmetic operators. However,
when NumLock is off, the numeric keypad is used as cursor movement keys.
Special keys
 Special keys are keys that are used to execute some commands. They also work in
combination with other keys to execute commands. These keys include: Shift, Alt, Ctrl etc.

4. 2. Mouse
 A mouse is a device that is rolled about on a desktop
to direct a pointer on the computer’s display screen.
The pointer is a symbol, usually an arrow that is
used to select items from lists (menus) on the screen
or to position the cursor.
 The cursor, also called an insertion point, is the
symbol on the screen that shows where data may be
entered next, such as text in a document.
Mouse consists of:
 Primary button (Left button)
 Secondary button (Right Button)
The following operations can be performed using the
mouse.
 Selection (Single click)
 Giving Commands (Double click)
 Dragging Objects (By pressing mouse button and moving the

5. Scanner
 Scanners translate images of text, drawings and photos into digital
form.
 The images can then be processed by a computer, displayed on a
monitor, inserted in documents, stored on a storage device, or
transmitted to another computer.
Based on the technology they use to scan, scanners are of the
following types:
BCR – Bar Code Reader
 A barcode reader (barcode scanner) is a computer peripheral
for reading barcodes printed on various surfaces. It generally
consists of a light source, a lens and a photo conductor
translating optical impulses into electrical ones.
OCR – Optical Character Reader
 OCR is a character recognition technology that is used to
recognize typewritten or handwritten characters.
OMR – Optical Mark Recognition

6. Processing devices
CPU
 The CPU is the brains of the computer. Sometimes
referred to simply as the processor or central
processor, the CPU is where most calculations take
place.
 In terms of computing power, the CPU is the most
important element of a computer system. Many
people wrongly call the system case (chasis) as
CPU. But the chasis is a housing for devices like
CPU, RAM, disks, motherboard and expansion
cards.
CPU has three components, namely:
1. The arithmetic logic unit (ALU), which performs
arithmetic (addition, subtraction, multiplication, and

7. 2. The control unit, which extracts instructions
from memory and decodes and executes them,
calling on the ALU when necessary.
3. The Memory unit or registers, which store
intermediate results of ALU
Storage devices
Storage Capacity Measurement
Bit (Binary Digit):
 The bit is the smallest unit of storage used in
computing.
 A bit of storage is like a light switch; it can be
either on (1) or off (0). A single bit is a one or a
zero, a true or a false, a "flag" which is "on" or

8.  Byte: Means 8 bits.
 KB (Kilo byte): A kilo byte is 210 bytes = 210 x 8 bits
 MB (Mega byte): A mega byte is 220 bytes = 220 x 8
bits.
 GB (Giga byte): A giga byte is 230 bytes = 230 x 8 bits
 TB (Tera byte): A tera byte is 240 bytes =240 x 8 bits
Primary storage
Cache memory
 Small memories on or close to the CPU chip can be
made faster than the much larger RAM (main
memory).
 Most CPUs since the 1980s have used one or more
caches, and modern general-purpose CPUs inside
personal computers may have as many as half a
dozen, each specialized to a different part of the

9. RAM (Random Access Memory)
 Generally, RAM in a computer is considered as main
memory or primary storage: the working area used
for loading, displaying and manipulating applications
and data.
 This type of RAM is usually in the form of integrated
circuits (ICs). These are commonly called memory
sticks or RAM sticks because they are manufactured
as small circuit boards.
 These days, most personal computers have slots for
adding and replacing memory sticks. RAM is also
volatile, losing the stored information in an event of
power loss, and quite expensive.

10. Read-Only Memory (ROM)
 Read-only memory (ROM) contains the computer's
permanent startup programs. ROM is nonvolatile; its
contents remain with or without power being applied.
 The chips and software (programs and data) that have
been written onto these chips are called firmware.
 The ROM chip contains the basic input/output system
(BIOS) that provides instructions and data to the
processor.
 The system ROM enables the computer to boot (start
the operating system). BIOS is the built-in software that
determines what a computer can do without accessing
programs from a disk.
 They contain all the code required to control the boot
process, and they control many hardware devices,
including the keyboard, display, screen, disk drives,
serial communications, and others.

11. Types of ROM
 ROM chips are written to during production and cannot
change content afterwards. But there are other types of
non-volatile solid-state memory:
 PROM (Programmable Read-Only Memory) can be
written to (programmed) via a special device, a PROM
programmer. The writing often takes the form of
permanently destroying The program.
 PROM can only be programmed once.
 EPROM (Erasable Programmable Read-Only Memory)
can be erased by ultraviolet light then rewritten via an
EPROM programmer.
 Repeated exposure to ultraviolet light will eventually
destroy the EPROM but it generally takes many (greater
than 1000) exposures before the EPROM becomes
unusable.
 EEPROM (Electrically Erasable Programmable Read-
Only Memory) allow the entire ROM (or selected banks
of the ROM) to be electrically erased (flashed back to

12. Secondary storage
 In computer storage, secondary storage, or external
memory, is computer memory that is not directly
accessible to the central processing unit of a
computer, requiring the use of computer's input/output
channels.
 Secondary storage is usually slower than primary
storage, or internal memory, but also almost always
has higher storage capacity and is non-volatile, which
makes it perfect for the preservation of stored
information in an event of power loss.
Magnetic tape
 Magnetic tape is a non-volatile storage medium
consisting of a magnetic coating on a thin plastic strip.

13. Magnetic disk
 Floppy Disk
 A floppy disk is a data storage device that is composed
of a disk of thin, flexible ("floppy") magnetic storage
medium encased in a square or rectangular plastic shell.
 Floppy disks are read and written by a floppy disk drive.
Floppy disk is cheap, and portable, but it has small
storage capacity (1.44 MB).
 Hard disk
 A hard disk drive (HDD) is non-volatile storage device
which stores data on rapidly rotating platters with
magnetic surfaces.
 Hard disks were originally developed for use with
computers. In the 21st century, applications for hard
disks have expanded beyond computers to include video
recorders, audio players, digital organizers, and digital
cameras.

14. Optical disk
 CD-R
 A CD-R (Compact Disc-Recordable) is a write once, read-only optical
magnetic media commonly known as optical disc (though the whole
disk does not have to be written in the same session).
 CD-RW (Compact Disc ReWritable)
 CD-RW is a rewritable optical disc format. Known as CD-Erasable (CD-
E) during its development, CD-RW was introduced in 1997.
 DVD(Digital Versatile Disc)
 DVD (sometimes called "Digital Versatile Disc", or "Digital Video
Disc") is an optical disc storage media format that can be used for data
storage, including movies with high video and sound quality.
 DVDs resemble compact discs as their physical dimensions are the
same but at a much higher capacity.
 Flash Memory
 USB flash drives -thumb drives, handy drives-, which are used for
general storage and transfer of data between computers.
 Flash memory is highly portable and it can store much data but it is

15. Output devices
Display devices – softcopy output
 CRT
 Abbreviation of cathode-ray tube, the technology used in
most televisions and computer display screens. It is large in
size and requires a lot of space. Moreover, it consumes much
power. But it produces a sharp output.
 LCD
 Short for liquid crystal display, a type of display used in
digital watches and many portable computers.
 Monochrome LCD images usually appear as blue or dark
gray images on top of a grayish-white background.
Color LCD displays use two basic techniques for producing
color:
1. Passive matrix is the less expensive of the two
technologies.
2. Active-matrix, produces color images that are as sharp as
traditional CRT displays, but the technology is expensive.
 The advantage is that it does not consume a lot of space
since it is thin and that it does not consume a lot of power

16.  Printer – hardcopy output
Printer is a device that prints text on paper. There are
many different types of printers. In terms of the
technology they utilize, printers fall into the following
categories:
 Daisy-wheel: this type of printer has a plastic or metal
wheel on which the shape of each character stands out
in relief.
 Daisy-wheel printers produce letter-quality print but
cannot print graphics.
 Dot-matrix: Each pin makes a dot, and combinations of
dots form characters and illustrations.
 Ink-jet: Sprays ink at a sheet of paper. Ink-jet printers
produce high-quality text and graphics.
 Laser: Uses the same technology as copy machines.
Laser printers produce very high quality text and
graphics.

17.  Speaker – voice output
 Speaker converts electrical signals into sounds
loud enough to be heard at a distance.
 It is used in computer system to produce sound
or voice output. The sound is input from
external world into computer system via
microphone and is output to external world via
speaker.
 Robot – physical output
 Robot Robotic device consists of arms that can
perform a preprogrammed task. Robots are
mostly used in manufacturing tasks such as
spray painting or assembling parts.

18.  Software Component
 Computer software is a set of step-by-step instructions given
to the computer in the form of programs in order to
accomplish any specified task.
 If software is stored on non-volatile storage such as
integrated circuits, it is usually referred to as firmware.
1. System software
 System software is an essential part of the computer
system. An operating system is an obvious example, while
device driver and language software are also examples.
 Operating system
 An operating system (OS) is a computer program that
manages the hardware and software resources of a
computer. At the foundation of all system software, the OS
performs basic tasks such as controlling and allocating
memory, prioritizing system requests, controlling input and
output devices, facilitating networking, and managing files.
 It also may provide a graphical user interface for higher level
functions. The operating system is considered as the boss of
the whole system.

19. Relationship between hardware, software and the
computer user is shown
System Software
Application Software
Users
Computer
Hardware

20. Basic functions of operating system are:
 input /output management
 Controls spooling and buffering, multitasking and
overlapping, time sharing and network.
 memory management
 Control the allocation of RAM for various purposes
like background and foreground program execution
priorities and virtual memory system.
 file management
 Under which files are stored on secondary storage
devices, where can be copied, sorted, displayed
and removed among other functions.
 job control (process scheduling)
 Which include executing programs on demand
from the user using utilities and other programs.

21. Device driver
 In theory a new device, which is installed in a
new manner should function correctly if a
suitable driver is available. This new driver will
ensure that the device appears to operate as
usual.
 In short, device driver is a type of system
software that introduces a new device to the
operating system and facilitates the
communication between the operating system
and the device.
Language software
 Languages
 Languages are used for writing instructions or
software. Basically, computer languages range

22.  Machine Language
 Machine language is the only language the computer directly
understands. It is in the form of strings of binary numbers. A machine
language instruction has at least two parts:
 opcode – function code which specifies the function performed and
 operand address – which specifies location of data and other
instructions
 Assembly Languages
 Assembly language is easier to use than machine language. It is
done by representing some of the most commonly used instruction
codes with some symbols.
 But it needs special translating program. It is machine dependent.
 High Level Languages
 High level languages resemble some human languages such as
English and are easier for human programmers to write.
 It allows users to write in a familiar notation, rather than numbers or
abbreviations. Most of high level languages are machine
independent.

23. Utility software
 Utility Programs are generally used to support, enhance or expand existing programs
in a computer system.
Examples of utility programs are
 Backup – to duplicate the data or information for safety.
 Data Recovery – to restore data that is physically damaged or corrupted.
 Virus Protection – Antivirus software which will eliminate viruses from
affected files or protect files from being infected from viruses.
 Data Compression – used to compress huge files and save memory
storage.
Application software
Unlike system software, application software, consists of programs that help the end-
user to perform specific, productive tasks, such as word processing or image
manipulation.
Categories of application software.
 Productivity Software: The purpose of this software is to make the users
more productive at performing general tasks. For example, word
processing, spread sheets, presentation, database managers, accounting
etc.
 Education / Reference software: The purpose of this software is mainly
to learn any subject or to refer for additional information.
For example: Encyclopedia, Dictionaries, Computer Based Tutorials