Computer System

Computer System / System Unit
Computer is an electronic device that
accepts an input, process and provides an
output.
Instructor Nganda Ivan. BBA BIS,
MBA(cand) FOSS
Module 2

Daily usage of Computers:
• Computers at home: internet, games, home
businesses
• Computers in education: audio visual aid in
schools, colleges, libraries. Classroom
presentation, computer labs, distance learning
etc.
• Computers in workplace: record keeping such as
accounting, medical, operations etc., Ecommerce,
communications, production lines: robots etc.
• Computers outdoor: ATM, GPS, sales catalog,
mall picture booth etc.
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Operations a computer performs
• Input: provide/feed data into the computer
• Processing: computer performs specific
operation on data determined by the user or
system
• Output: computer outcomes the result
• Storage: computer stores data, programs as
input/output for future use
• The above operations are abbreviated as IPOS.
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Flow of computer operations
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Hardware and Software:
• Hardware:
• Physical part of the computer. Hardware can
be internal or external.
• Internal Hardware: located inside the system
unit of the computer. Example: CPU, RAM,
processor etc.
• External Hardware: located outside of the
system unit. Example: keyboard, monitor,
printer, portable drive etc.
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Divisions of hardware:
• Input Devices: An input device is used to input
data into the computer. Example: keyboard,
mouse, joystick etc.
• Processing Devices: A processing device performs
calculations and comparisons necessary for
processing. The main processing device is the
central processing unit (CPU). It is the “brain” of
the computer.
• Output Devices: An output device presents the
results to the user. Examples: monitor, printer,
headphone etc.
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Divisions of Hardware
• Storage devices: Storage devices are used to
save data, programs or output. Examples: hard
drive, floppy diskette, CD discs etc.
• Communication Devices: Communication
devices allow the user to communicate with
others and access remote information.
Examples: modem, network card etc.
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Software:
• The programs or instructions used to tell the
computer hardware what to do
• Software are written in codes so that
computer hardware understand the
• Tasks to be performed. Software can be
installed in the hard drive, or run in RAM or
can be assessed from a remote location.
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Two basic types of software:
System software and Application software.
• System software: allows a computer to
operate and run application software.
Examples: Windows, Linux etc.
• Application software: performs specific tasks
or applications. Example: customized
software, MS Office, games, Real Player etc.
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JARGONS
• Data = raw, unorganized facts. Can be in the form
of text, graphics, audio, or video.
• Information = data that has been processed into a
useful form
• Information processing: conversion of data to
information
• Computer users or end users: are the people who
use a computer to obtain information
• Programmers: are computer professionals whose
job it is to write the programs that computers use
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Networks and Internet:
• A computer network links computers together so that users can
share hardware, software, and data, as well as electronically
communicate with each other.
• Network uses a network server to manage the data flowing through
the network devices.
• Server: A server is a powerful computer in the network that serves
clients in terms of providing access, sharing devices within the
network.
• Client: Clients are computers on the network that access resources
via the network server
• Examples of network: home network, computer lab network, office
network, network across states etc.
• Thin client: Uses server’s disk drive for storage and CPU for
processing. Advantage: Low cost. Disadvantage: Limited storage and
slow rate of processing.
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Network Illustration
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History of internet:
• ARPANET
• 1956: US Govt. funded to create ARPA under Defense
Department
• 1969: Four universities were connected through Packet
Switching Network. It used Net Control Protocol.
• 1971: Creation of Email
• NCP became insufficient so TCP (Transmission Control
Protocol) was introduced
• 1983:TCPIP used to connected to Internet
• NFS Net
• 1993: NFS became Internet
• 1993: Creation of URL, First graphic browser
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Five basic categories of computers:
• Mobile devices: Examples: PDA
• Personal computers: Example: Desktop PC, Notebook
computers or laptop
• Midrange servers: Fall between microcomputers and
mainframes in processing power. Used in small
network
• Mainframe computers: Standard choice for most large
organizations. Specialize in high-volume processing
• power
• Supercomputers: Used for applications that have
extraordinary demands for processing power. Offer
very fast speeds and extreme degrees of accuracy
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Components of a system Unit
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• The system unit, sometimes called the chassis, is a box-like case
housing the electronic components of a computer that are used to
process data.
• System unit components include the processor, memory module,
cards, ports, and connectors.
• Many of the system unit’s components reside on a circuit board
called the motherboard.
• The motherboard contains many different types of chips, or small
pieces of semiconducting material, on which one or more
integrated circuits (IC) are etched.
• An integrated circuit is a microscopic pathway capable of carrying
electronic current.
• Each IC can contain millions of transistors, which act as switches for
electronic signals.

Types of Memory
• Memory is a temporary storage place for data, instructions,
and information.
• Memory stores the operating system, application programs,
and the data processed by application programs.
• A byte is the basic storage unit in memory. Memory size is
measured by the number of bytes available for use.
• A kilobyte (KB or K) of memory is approximately one
thousand bytes,
• A megabyte (MB) is approximately one million bytes,
• A gigabyte (GB) is approximately one billion bytes.
• The system unit contains several types of memory.
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Computer Memory
• RAM (random access memory) consists of memory
chips that the processor can read from and write to.
• Most RAM is volatile memory, meaning that its
contents are lost when the computer’s power is turned
off.
• Two basic types of RAM chips are dynamic RAM and
static RAM.
• Dynamic RAM (DRAM) must be re-energized
constantly or it loses its contents.
• Static RAM (SRAM) is faster and more reliable than
DRAM and has to be re-energized less often, but it is
much more expensive.
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Computer Memory
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• Memory cache, also called a cache store or RAM cache, improves
processing time by storing frequently used instructions and data.
• ROM (read-only memory) refers to memory chips that only can be read
and used; that is, they cannot be modified.
• ROM is nonvolatile memory (NVM), meaning that its contents are not lost
when the computer’s power is turned off.
• A variation of the ROM chip, called programmable read-only memory
(PROM), is a blank chip on which you can place items permanently.
• Flash memory, also known as flash ROM or flash RAM, is nonvolatile
memory that can be erased electronically and reprogrammed.
• Complementary metal-oxide semiconductor (CMOS) memory, another
type of memory chip, stores configuration information about the
computer and uses battery power to retain information when the power
to the computer is off.

Computer Slots
• An expansion slot is an opening, or socket, where you
can insert a circuit board into the motherboard.
• These circuit boards – called cards, expansion cards,
boards, expansion boards, adapters, adapter cards,
interface cards, add-ins, or add-ons -- add new devices
or capabilities to the computer.
• Four types of expansion cards found in most computers
are
– video card,
– sound card,
– network interface card,
– modem card.
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Cards Unleashed
• A video card converts computer output into a video signal that is sent
through a cable to the monitor, which displays an image.
• A sound card enhances the sound-generating capabilities of a personal
computer by allowing sound to be input through a microphone and output
through speakers.
• A network interface card (NIC) is a communications device that allows the
computer to communicate via a network.
• A modem card is a communications device that enables computers to
communicate via telephone lines or other means.
• Many of today’s computers support Plug and Play, a capability with which
the computer automatically can configure expansion boards and other
devices as you install them.
• Notebook and other portable computers have a special type of expansion
slot used for installing a PC Card, which is a thin credit card-sized device
that adds memory, disk drives, sound, fax/modem, and communications
capabilities to a mobile computer.
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a serial, a parallel, and a USB port
• A cable often attaches external devices to the system unit.
• A port is the interface, or point of attachment, to the system unit. Ports have
different types of connectors, which are used to join a cable to a device.
• Male connectors have one or more exposed pins, while female connectors have
matching holes to accept the pins.
• Most computers have three types of ports: serial, parallel, and USB. A serial port is
a type of interface that connects a device to the system unit by transmitting data
only one bit at a time.
• Serial ports usually connect devices that do not require fast data transmission
rates, such as a mouse, keyboard, or modem.
• A parallel port is an interface that connects devices by transferring more than one
bit at a time.
• Many printers connect to the system unit using a parallel port.
• A universal serial bus (USB) port can connect up to 127 different peripheral
devices with a single connector type, greatly simplifying the process of attaching
devices to a personal computer.
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Buses & computer's processing speed
• Bits are transferred internally within the circuitry of the computer along
electrical channels.
• Each channel, called a bus, allows various devices inside and attached to
the system unit to communicate with each other.
• The bus width, or size of the bus, determines the number of bits that can
be transferred at one time.
• The larger the bus width, the fewer number of transfer steps required and
the faster the transfer of data.
• In most computers word size (the number of bits the CPU can process at a
given time) is the same as the bus width.
• Every bus also has a clock speed. The higher the bus clock speed, the
faster the transmission of data, which results in applications running
faster.
• A computer has two basic types of buses. A system bus connects the CPU
to main memory. An expansion bus allows the CPU to communicate with
peripheral devices.
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Hand Held Computers
• Handheld computers run strictly on battery.
Similar to desktop and notebook computers,
handheld computers have a system unit that
contains electronic components that process
data.
• A handheld computer’s system unit also contains
a display and may house speakers and some form
of keyboard and/or pointing device.
• Handheld computers often have an IrDA port so
you can communicate wirelessly with other
computers. Many also include a serial port.
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Input & Output Devices
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illustration
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Input Devices
• a. Keyboard,mouse,joystick,scanners,digital
camera, bar code
• reader, touch Sreeen,Speech input device
(microphone)
Output Devices
• a. Monitor , Speaker, Printers ( different types)
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Introduction
• The computer will be of no use unless it is able to
communicate with the outside
• world. Input/Output devices are required for
users to communicate with the computer.
• In simple terms, input devices bring information
INTO the computer and output
• devices bring information OUT of a computer
system. These input/output devices are
• also known as peripherals since they surround
the CPU and memory of a computer system.
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• Some commonly used Input/Output devices are listed in table below.
Input Devices
• Keyboard
• Mouse
• Joystick
• Scanner
• Light Pen
• Touch Screen
Output Devices
• Monitor
• LCD
• Printer
• Plotter
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Keyboard & Its Keys
a) Keyboard
• It is a text base input device that allows the user to
input alphabets, numbers and other characters. It
consists of a set of keys mounted on a board.
Alphanumeric Keypad
• It consists of keys for English alphabets, 0 to 9
numbers, and special characters like + − / * ( ) etc.
Function Keys
• There are twelve function keys labeled F1, F2, F3… F12.
The functions assigned to these keys differ from one
software package to another. These keys are also user
programmable keys.
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Keyboard Keys
Special-function Keys
• These keys have special functions assigned to them and can be used
only for those specific purposes. Functions of some of the
important keys are defined below.
Enter
• It is similar to the ‘return’ key of the typewriter and is used to
execute a command or program.
Spacebar
• It is used to enter a space at the current cursor location.
Backspace
• This key is used to move the cursor one position to the left and also
delete the character in that position.
Delete
• It is used to delete the character at the cursor position.
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Keyboard keys
Insert
• Insert key is used to toggle between insert and overwrite mode during data entry.
Shift
• This key is used to type capital letters when pressed along with an alphabet key.
Also used to type the special characters located on the upper-side of a key that has
two characters defined on the same key.
Caps Lock
• Cap Lock is used to toggle between the capital lock features. When ‘on’, it locks the
alphanumeric keypad for capital letters input only.
Tab
• Tab is used to move the cursor to the next tab position defined in the document.
Also, it is used to insert indentation into a document.
Ctrl
• Control key is used in conjunction with other keys to provide additional
functionality on the keyboard.
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Keyboard Keys
Alt
• Also like the control key, Alt key is always used in combination with
other keys to perform specific tasks.
Esc
• This key is usually used to negate a command. Also used to cancel
or abort executing programs.
Numeric Keypad
• Numeric keypad is located on the right side of the keyboard and
consists of keys having numbers (0 to 9) and mathematical
operators (+ − * /) defined on them. This keypad is provided to
support quick entry for numeric data.
Cursor Movement Keys
• These are arrow keys and are used to move the cursor in the
direction indicated by the arrow (up, down, left, right).
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Mouse
• (b) Mouse
• The mouse is a small device used to point to a particular place on
the screen and select in order to perform one or more actions. It
can be used to select menu commands, size windows, start
programs etc.
• The most conventional kind of mouse has two buttons on top: the
left one being used most frequently. Mouse Actions
• Left Click : Used to select an item.
• Double Click : Used to start a program or open a file.
• Right Click : Usually used to display a set of commands.
• Drag and Drop : It allows you to select and move an item from one
location to another. To achieve this place the cursor over an item on
the screen, click the left mouse button and while holding the
button down move the cursor to where you want to place the item,
and then release it.
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(c) Joystick
• The joystick is a vertical stick which moves the
graphic cursor in a direction the stick is
moved. It typically has a button on top that is
used to select the option pointed by the
cursor. Joystick is used as an input device
primarily used with video games, training
simulators and controlling robots
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(d)Scanner
• Scanner is an input device used for direct data
entry from the source document into the
computer system. It converts the document
image into digital form so that it can be fed
into the computer.
• Capturing information like this reduces the
possibility of errors typically experienced
during large data entry.
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Scanners
• Hand-held scanners are commonly seen in big stores to
scan codes and price information for each of the items.
They are also termed the bar code readers.
(e) Bar codes
• A bar code is a set of lines of different thicknesses that
represent a number. Bar Code Readers are used to
input data from bar codes. Most products in shops
have bar codes on them. Bar code readers work by
shining a beam of light on the lines that make up the
bar code and detecting the amount of light that is
reflected back
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(f) Light Pen & Touch Screen
• It is a pen shaped device used to select objects on a display
screen. It is quite like the mouse (in its functionality) but
uses a light pen to move the pointer and select any object
on the screen by pointing to the object.
• Users of Computer Aided Design (CAD) applications
commonly use the light pens to directly draw on screen.
Touch Screen
• It allows the user to operate/make selections by simply
touching the display screen.
• Common examples of touch screen include information
kiosks, and bank ATMs.
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(h)Digital camera
• A digital camera can store many more pictures
than an ordinary camera.
• Pictures taken using a digital camera are
stored inside its memory and can be
transferred to a computer by connecting the
camera to it.
• A digital camera takes pictures by converting
the light passing through the lens at the front
into a digital image.
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II. Output Devices
(a) Monitor
• Monitor is an output device that resembles the television screen
and uses a Cathode Ray Tube (CRT) to display information.
• The monitor is associated with a keyboard for manual input of
characters and displays the information as it is keyed in.
• It also displays the program or application output. Like the
television, monitors are also available in different sizes.
(b) Liquid Crystal Display (LCD)
• LCD was introduced in the 1970s and is now applied to display
terminals also.
• Its advantages like low energy consumption, smaller and lighter
have paved its way for usage in portable computers (laptops).
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(c) Printer
• Printers are used to produce paper (commonly known as hardcopy)
output. Based on the technology used, they can be classified as Impact or
Non-impact printers.
• Impact printers use the typewriting printing mechanism wherein a
hammer strikes the paper through a ribbon in order to produce output.
Dot-matrix and Character printers fall under this category.
Non-impact printers do not touch the paper while printing.
They use chemical, heat or electrical signals to etch the symbols on paper.
Inkjet, Deskjet, Laser, Thermal printers fall under this category of printers.
• When we talk about printers we refer to two basic qualities associated
with printers: resolution, and speed. Print resolution is measured in terms
of number of dots per inch (dpi).
• Print speed is measured in terms of number of characters printed in a unit
of time and is represented as characters-per-second (cps), lines-per-
minute (lpm), or pages-per-minute (ppm).
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(d) Plotter
• Plotters are used to print graphical output on
paper.
• It interprets computer commands and makes line
drawings on paper using multicolored automated
pens.
• It is capable of producing graphs, drawings,
charts, maps etc.
• Computer Aided Engineering (CAE) applications
like CAD (Computer Aided Design) and CAM
(Computer Aided Manufacturing) are typical
usage areas for
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(e) Audio Output: Sound Cards and
Speakers:
• The Audio output is the ability of the computer to
output sound. Two components are needed:
Sound card – Plays contents of digitized
recordings, Speakers – Attached to sound card.
Summary:
• The Chapter has given an introduction to the
Input/Output devices.
• It gives a detailed listing of the various types of
input devices and the output devise.
• The concepts are also very clearly understood by
seeing at the figures in the chapter.
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