2.1.6 Output Devices
Output from a computer system may be used by the decision makers at all levels of an
organization. Output can take two basic forms. It can be either printed on paper or any
other permanent media. Also it can be displayed on a screen or output by other nonpermanent
means. This is called a softcopy such as on a floppy disk.
Sometimes the output from one computer can be an input to another computer. The form
of output might be visual, audio or digital.
Visual Display Unit (VDU)/Monitors
The display monitor is a TV-screen like device on which output from the computer is
displayed. A pixel is a dot of color on a photo image or a point of light on a display
screen. It can be in on or off mode. The quality of a screen is often measured by the
number of horizontal and vertical pixels used to create it. A monitor’s ability to display
color is a function of the quality of the monitor, the amount of RAM in the computer
system and the monitor’s graphics adapter card. The color graphics adapter (CGA) was
one of the first technologies to color images on the screen. Today it has changed to
super video graphics array (SVGA), providing vivid colors and superior resolution.
There are different types of VDUs. Based on the range of colors they can display two
types can be identified:
• Monochrome display screens
• Color display screens
Monochrome display screens can display only one color text on single color background,
i.e. white letters on blue, or green characters on black. In color screens various colors
can be displayed.
Another way of grouping them is based on their internal structure. The most common
type of monitor uses a cathode ray tube (CRT). Liquid Crystal Display (LCD) screens are
used in laptops. LCD monitors use the same technology which used for pocket
calculators and digital watches. This is a good solution especially if you do not have desk
space for a large CRT monitor or you need a portable computer. Plasma screens are
used for very large screens and in some modern laptops. They are flat screens with
good color, but are quite expensive. These screens are much easier on human eye
comparing to the CRT monitors. If you are using the monitor for long periods it is better
to purchase a high priced, low power consuming LCD panel, but if your usage is not
that frequent you could go for a low cost CRT monitor.
Printers
The job of a printer is to put on paper what you see on your monitor. How easy and how
successfully it is done depends on the choice of your printer. Selection of a printer is
based on many parameters such as cost, speed, type of paper used, quality or
resolution, size, type of cable connection etc. There are different types of printers. The
less expensive but a noisy version is a Dot matrix printer whereas expensive ones are
inkjet and laser printers. These are capable of producing high quality printouts and their
biggest advantage is that they are noiseless.
Plotters
A plotter consists of a device that can move paper both backwards and forwards. On the
top of the device one or more pens are able to move horizontally across the paper. The
combined movement of the pens horizontally across the paper and the vertical
movement of the paper allows complex continuous diagrams to be drawn. A plotter is a
specialized output device designed to produce high-quality graphics. Plotters are
especially useful for creating maps and architectural drawings, although they may also
produce less complicated charts and graphics.
Some plotters allow different colour pens to be used to create diagrams in multiple
colours.
In other types of plotters, the paper lies on a flat bed. The mechanics of the plotter are so
designed that the pens can move both across and down the paper to create the diagram.
Computer Output Microfilm Devices
Companies use computer output microfilm devices to place data from the computer
directly onto microfilm for future use.
Music Devices
MP3 is a standard format for compressing a sound sequence into a very small file while
preserving the original level of sound quality when it is played. Compressed sound file
requires less time to download the file and less storage space on a hard drive. MP3 is
facing competition from Windows Media from Microsoft, RealNetwork’s Real Audio and
an upgraded version of MP3 is called mp3PRO.
2.1.5 Input Devices
Input devices allow users to enter data and information to the computer system. When
selecting input devices it is important to balance the speed and functions performed by
the input devices with their cost, control and complexity. Input devices vary from capture
specific types of data to more general purpose input devices. Following are some
examples.
Keyboard
The keyboard is also referred to as the primary input device of the computer system. The
keyboard has a similar layout to the typewriter, but has some additional keys that provide
additional functionality than a typewriter. In a computer, a keyboard converts letters,
numbers and other characters into electrical signals that are computer readable. These
special keys are Insert key, Enter key, Home key, Ctrl key, Alt key, etc. Keyboards come
in different shapes and sizes and may differ in the number of additional keys.
Pointing devices
Although keyboards are still the mostly widely used input devices to enter text into a
computer system, pointing devices are a better alternative for issuing commands and
responding to prompts displayed on the monitor. They work with the operating systems
Graphical User Interface (GUI) that presents you with icons, menus, windows, bars and
so on for your selection. Pointing devices use one of the most natural gestures of
humans i.e. the act of pointing. Mouse, trackballs, joysticks, touch screens are some of
the most frequently used pointing devices.
Mouse
The mouse is the second most common input device. A ball underneath rolls as
the mouse moves across the mouse pad.The cursor on the screen follows the
movement of the mouse. Buttons on the mouse can be clicked or double -clicked
to perform tasks, like to select an icon on the screen or to open the selected
document. There are new mouse models that do not have a ball. They use a
laser to sense the motion of the mouse instead.
Trackball
Trackball is a movable ball, on top of a stationary device, that is rotated with the
fingers or palm of the hand. Advantages of trackballs are that, it does not need as
much desk space as a mouse, and it is not as tiring since less motion is needed.
On the other hand it requires fine control of the ball with just one finger or thumb.
Joystick
A joystick is a pointing device that consists of a vertical handle like a gearshift
lever mounted on a base with one or two buttons. Joysticks are commonly used
in video games to control the cursor motion. A joystick gives a more natural
feeling of control for motion in games, especially those in which one is mimicking
flying a plane or spaceship.
Voice/Speech Recognition Systems
These devices can recognize human voices. These tools use microphones and special
software to record and convert the sound of the human voice into digital signals.
Speech recognition systems can be used on the factory floor to allow equipment
operators to give basic commands to machines while they are using their hands to
perform other operations. Voice-recognition is also used in security systems to allow only
authorized personnel into restricted areas. Since speech is the easiest, most natural
means of communication, speech recognition promises to be the easiest method for data
entry, word processing and conversational computing.
Digital Cameras
Digital cameras look very similar to regular cameras but record and store images or
video in digital form. After taking a picture, the images are electronically stored in the
camera.
Most often the image file is compressed and stored on the digital memory card to allow a
large number of photographs to be taken. The memory card is displayed like
another disk drive on your computer system when you connect the digital camera to the
computer system. Then images stored on the card can be downloaded to the computer
with the help of a cable which is connected from the camera to a port on the computer.
Alternatively, the images stored in the flash memory card of the diskette can be
downloaded by inserting it to the personal computer.
Terminals
Terminals are input devices that perform data entry and data input at the same time.
Data entry and input is through the keyboard and mouse. A terminal is connected to a
complete computer system by telephone lines or cables. They are inexpensive and easy
to use.
Point-of-Sale (POS) devices are terminals used in retail operations to enter sales
information into the computer system.
Magnetic Ink Character Recognition (MICR) Devices
Magnetic Ink Character Recognition (MICR) devices are used to read the data that is
placed at the bottom of a check or other form using a special magnetic ink. Humans as
well as computers can read this data. This technology is used by banks.
Light Pens
The light pen is a light-sensitive stylus, or a pen like device connected to the computer.
The user can bring the pen to the desired point on the screen. When the pen touches the
screen, it sends the information available at the location to the computer. Using the pen
input device it is possible to activate a command or cause the computer to perform a
task, enter handwritten notes and draw objects and figures.
These can be used to activate commands and place drawings on the screen.
Touch-Sensitive Screens
Touch screen is a video display screen that receives input from the touch of a finger or
stylus. These screens can act as input as well as output devices. Examples are
Automatic Teller Machines (ATMs) in banks and information kiosks.
Scanning Devices
Scanners generally convert text, drawings and photographs into digital form that can be
stored in a computer and then manipulated. Sometimes these scanners are called image
scanners or graphics scanners.
There are special purpose scanners such as fingerprint scanners which are used to scan
finger prints and barcode readers.
Barcodes are a set of dark lines that are used to uniquely identify an item or product.
Barcodes are found in many products ranging from books to canned fruits. This is a
convenient way of entering data without using a mouse or a keyboard by simply swiping
the printed barcode under the barcode reader.
These emit strips of LASER light and the reflected image is picked up by the light
sensors. The captured image is processed and the barcode is identified and passed on
to the computer system as an alphanumeric value. This value can be processed by the
program and a suitable response can be executed.
In retail operations barcode scanners are usually connected to POS devices. POS
devices are terminals used in retail operations to enter sales information into the
computer system.
2.1.4 Secondary Storage
Organizations need to store large amounts of data and instructions more permanently
than allowed by the main memory. Secondary storage can be used for this purpose. It is
also called the permanent storage. There are different types of secondary storage
mediums such as magnetic discs and tapes. We discuss these in detail in the following
sub-sections.
Compared to Memory, secondary storage is non-volatile (i.e. data is not lost when
electrical power is switched off) and less expensive. The disadvantage is, it is much
slower than the memory. When selecting a secondary storage media and devices, it is
important to consider the access method, capacity and portability. Secondary storage
media with faster access methods are generally more expensive than slower media. Lets
consider what is meant by access method.
Access Methods
There are two methods of accessing data in the storage. They are, sequential and direct
access methods.
Sequential access – This means that data must be accessed in the order in which it is
stored. For example, product data stored sequentially may be stored by product number
ranging from 10 to 30 in a secondary storage device. If you want to retrieve information
on product number 25, you have to read and discard data relating to product numbers
from 10 to 24.
Direct Access – According to this method data can be accessed directly, without the
need to bypass other data in the sequence. If you consider the earlier example, you can
directly access information relating to product number 25. Therefore, this access method
is much faster than sequential access.
2.1.4.1 Magnetic Tape
Magnetic tape is a thin plastic tape on which data can be represented with magnetized
spots. The magnetic tape used for computers, is made from the same material used for
audiotape and videotape. Magnetic tape is kept on a large open reel or in a small
cartridge or cassette. Although this is an old technology, it remains popular because it is
the cheapest storage medium and can handle enormous amount of data. The downside
is that it isthe slowest for retrieval of data, because all the data are placed on the tape sequentially.
This means as explained earlier, the system might have to run through a major part of
the tape, before it comes to the desired piece of data.
2.1.4.2 Magnetic Disks
Magnetic disks come in a variety of styles and are extremely popular because they allow
much more rapid access to data compared with magnetic tape. The magnetic disk is like
a phonograph record in that it has tracks, and like a pizza in that it is divided into wedges
that are called sectors. Every piece of data has an address attached to it corresponding
to a particular track and sector. Any piece of desired data can be retrieved in a nonsequential
manner, by direct access. A read-write head uses the data address to quickly
locate and read the data.
2.1.4.3 Disks
Hard Disks
Hard drives use stacks of rigid magnetic disks. These disks are permanently mounted as
a unit that may be internal or external to the computer. The data transferred to and from
the computer is handled by the read/write heads. The read/write heads are attached to
arms that hover over the disks moving in and out. They read the data when positioned
over the correct track and when the correct sector spins by. Because the head floats just
above the surface of the disk (at 25 millionths of a meter), any bit of dust or
contamination can disrupt the device.
For that reason, hard drives are hermetically sealed when manufactured. A modern
personal computer may have several gigabytes of storage capacity in its internal hard
drive. Data access is very fast. For these reasons, hard disk drives are extremely
popular and common.
Floppy Disks
Magnetic diskettes are commonly called floppy disks and function similarly to hard
drives, but with some key differences. A floppy disk is a removable round, flat piece of
plastic that stores data and programs as magnetized spots. This is enclosed in a
rectangular plastic case. The basic sizes of the diskettes are 3½ inch which is now more
popular in 5¼ inch. A floppy drive copies or reads data from disk and writes or records
data to the disk.
Diskettes are often called “floppy” because the disk with the case is flexible. They are
much slower than hard drives. They have much less capacity, ranging from 1.44
megabytes for a standard high density disk to 200 megabytes for a disk formatted for a
zip drive (on which the data are compressed). Further, although they are individually
inexpensive floppy disks are less cost-efficient than hard drive storage. However, the big
advantage of floppy disks is that they are portable.
Optical Disks
An Optical Disk is a removable disk on which data is written and read through the use of
a laser beam. Few types of optical technologies are used in computers. They are:
• Compact Disk Read -Only Memory (CD-ROM)
CD-ROM technology uses 12cm compact disks similar to those used in stereo music
systems. Compact Disk Read -Only Memory (CD-ROM) storage devices feature high
capacity (more than 600MB can be stored in a disk), low cost, and high durability.
However, as it is a read –only medium, the CD-ROM can only be read and not written
on. CD-ROM disk drives use a laser device to read the binary codes formed by those
pits.
• Write Once Read Many Disk (WORM)
Write Once Read Many Disk can be written or recorded onto once and then cannot be
erased. But it can be read many times.
• Rewritable Compact Disk
Rewritable Compact Disks allow user to rewrite onto the CD.
2.1.3 Main Memory
provides you with working storage your computer needs to process applications.
Memory devices contain thousands of circuits imprinted on a silicon chip. The circuit
either conduct electrical current or not. Data is stored in memory as a combination of on
or off circuit states. Computer stores data using the binary system. That is, it has only
two digits 0 and 1. Binary concept was originated from switching ON and OFF electricity.
In the computer, 0 represents the electrical current OFF and 1 by the current being ON.
It is important to know how many 0s and 1s can be stored in a computer? This is referred
to as the memory capacity. In a binary system, each 0 or 1 is called a bit, which is short
for binary digit. To represent numbers, letters or special characters such as & or ), bits
are combined into groups.
A group of 8 bits is called a byte, and a byte can represent one character, digit or other
value. For an example, 0100 0001 represents the letter A. The capacity of computer
memory or a diskette is expressed in numbers of bytes. Generally, it is given in kilobytes
or megabytes.
• Kilobyte :Kilo means one thousand, so a kilobyte (KB) is approximately one thousand bytes. Actually, a kilobyte is 1,024 (2 10) bytes. • Megabyte :Mega means one million, so a megabyte (MB) is approximately million bytes. Actually a megabyte is 1,048,576 (2 20) bytes. • Gigabyte :Giga means one billion, a gigabyte (GB) is actually 1,073,741,824 (2 30) bytes. • Terabyte :Tera means one trillion, a terabyte (TB) is actually 1,099, 511,627,776 (2 40) bytes.
To get a feel for these amounts, consider the following examples. If your computer has
32 MB of RAM (a type of primary storage explained later), it can store 33,554,432 bytes
of data. A written word might, on average, contain 6 bytes, so this translates to
approximately 5.6 million words
Types of Main (Primary) Memory
There are several forms of primary memory. They include Random Access Memory,
Read Only Memory and cache memory.
Random Access Memory (RAM)
small storage locations are called cells. Each cell has a unique number assigned to it
and this unique number is called the address of the cell and is used to identify the cell.
This memory can be compared to a large filing cabinet containing as many drawers as
there are addresses in memory. Each drawer contains a word and the address is written
on the outside of the drawer as in figure 2.2.
This memory is referred to as the Random Access Memory because the memory
locations of the Random Access Memory can be directly accessed to store and retrieve
data (we discuss about storage access methods in section 2.1.4) Whenever the
computer wants to work with data or instructions, they are first loaded in to RAM where
they are held temporarily until the computer needs them. Therefore, the storage of data
and instructions inside RAM is temporary and data and information which have been
stored will disappear from RAM as soon as the computer is switched off. RAM is
therefore volatile ie. it loses its content when the power is switched off.
Read Only Memory (ROM)
therefore, ROM is known as non-volatile memory.
Unlike RAM, ROM can only be read by the CPU and cannot be erased or overwritten. It
provides permanent storage for data and instructions that do not change.
Examples: Data from the computer manufacturer The instructions that tells the computer how to start up when power is turned on.
Cache Memory
performance has not been able to keep pace with this change. Therefore, processing
speed has not increased due to the slow speed of RAM. To reduce this mismatch in
operating speed, a small memory chip is attached between CPU and RAM. This memory
is called Cache Memory. The access time is close to the processing speed of CPU. The
CPU will first retrieve data from the Cache Memory. If the data is not available in the
Cache Memory, then the data is first loaded from RAM into the Cache Memory, and then
taken by the CPU from the Cache Memory as shown in Figure 2.3.
As the cache memory has got less amount of data, usually, the CPU can access the
desired data and instructions more quickly than if it were selecting from the larger set in
main memory.
As the Cache Memory is accessed much faster than conventional RAM, it is used to
store programs or data currently being executed or temporary data frequently used by
the CPU. So the Cache Memory makes the RAM to be faster and it also supplements
the RAM. As discussed above the cache memory increases the overall performance of
the computer system. However, cache Memory is expensive than Main Memory.
2.1.2 The Central Processing Unit (CPU)
The CPU consists of several components. They are as follows;
1. Arithmetic/Logic unit
the speed of those devices. As you know, arithmetic operations such as addition,
subtraction, multiplication, and division are fundamental to all mathematical operations.
Logical operations are comparisons. That is, the ALU compares two pieces of data to
see whether one is equal to (=), greater than (>), or less than (<) the other.
2. Control unit
out program instructions. It directs the movement of data and instructions between the
main memory and the ALU. It also carries out the controlling of input and output devices
and passing of data to the ALU for computation.
3. Registers
They hold various types of information such as data, instructions, memory addresses
and the intermediate results of calculations. Essentially, they hold the data and
instructions that the CPU is currently working with and they can be thought of as being
the CPU’s workspace. As soon as a particular instruction or piece of data is finished with,
the next ones immediately replace it and information that results from the processing is
returned to main memory. Data and instructions do not go into either the Arithmetic/Logic
Unit (ALU) or the Control Unit (CU). The ALU works on the data held in the registers
acting on the instructions that are also held there.
Efficient processing and timely output is important to an organisation. Let’s consider
some factors which affect the processing speed of a processor.
Machine Cycle Time
machine cycle occurs is measured in fractions of a second.
Early computer operating speeds were measured in milliseconds (thousands of a
second) range. New computers operate nanoseconds (millionth of a second) and
picoseconds (trillionth of a second).
It is also measured in terms of how many instructions are executed in a second. This
is known as MIPS (millions of instructions per second)
Clock Speed
clock speed, which affects machine cycle time.
Clock speed is measured in megahertz.
Hertz – One cycle or pulse per second
Megahertz (MHz) – Measurement of cycles in millions of cycles per second
Gigahertz (GHz) – Billions of cycles per second
Wordlength and Bus Line Width
or 1. Number of bits the CPU can process at one time is known as the wordlength of
the CPU. The amount of data that can be transferred between devices in the same
machine cycle depends on the wordlength.
Data is transferred from the CPU to other system components through bus lines, the
physical writing that connects the computer system components. The number of bits
a bus line can transfer at any one time is known as bus line width.
Machine cycle time, clock speed, wordlength and bus line width affects the processing
speed of the CPU. When selecting a CPU, organizations must balance the benefits of
speed with cost. CPUs with faster clock speeds and machine cycle times are usually
more expensive than slower ones. CPU speed is also related to complexity. As
discussed in the next section, having a high speed cache memory can also increase the
speed of the CPU.
Lesson 2: Information Technology Concepts
2.1.1 Overview of Hardware of a Computer System
basic system functions of input, processing, output, storage and control.
The hardware components of a computer system include input and output devices, the
CPU, and primary and secondary storage devices. The selection of these hardware
components depends on organisational goals and IS objectives.
Input
telecommunications network into a computer system. Popular input devices include
keyboard and the mouse.
Processing
is accomplished by an interplay between one or more of the central processing units and
primary storage (main memory). These two are housed together in the same box orcabinet, named the system unit. Other computer system devices are linked to the system
unit directly or indirectly.
human understandable form for presentation for end users. Common output devices are
monitors and printers.
processing application, data will be fed to the computer with a set of necessary
instructions which is called a computer program. These data and programs, when they
are fed, should be stored inside the computer during the processing. But the computer
will generally store these information, data and programs temporarily. When the
computer is switched off, information stored will disappear. This storage is referred to as
the Primary storage where program instructions and data are held immediately before,
during and after execution by the CPU. Before you switch off your computer, data and
instructions should be permanently stored for later or future use. The devices used to
store data in a relatively permanent form are called Secondary storage. Thus, there are
two types of storage devices namely:
• Secondary storage devices
Control
the control unit. The control unit takes care of step by step processing of all operations
inside the computer. It controls how instructions are executed and the above operations
are performed.
