COM111
Lecture Schedule 3
Data Representation in Computers, Computer
Memory and Storage, Input Output Media
and Current Trends in Computer
Data Representation
in Computers
The number system used in day to day life
is decimal number system. Decimal number system has a base 10 and uses 10
digits from 0 to 9. As a computer professional it is necessary to understand
the following number systems frequently used in computers.
Ø Binary number system
which has a base 2 and uses 2 digits 0, 1
Ø Octal number system
which has a base 8 and uses 8 digits from 0 to 7
Ø Hexadecimal number
system which has a base 16 and uses 16 digits/letters from 0 to 9 digits, A-F
letters.
Possible
conversion among bases
Quantities / Counting
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Computer Memory and Storage
Computer memory refers to the electronic
holding place for instructions and data where the processor can reach quickly.
It can be classified into two broad categories: Primary memory and Secondary
memory.
The primary memory allows the computer to store
data for immediate manipulation and to keep track of what is currently being
processed. It is volatile, means that when the power is turned off, the
contents of primary memory are lost forever.
The secondary memory stores data permanently
and it is non-volatile storage medium. The secondary storage devices like the
hard disk have a larger storage capacity, less expensive as compared to primary
storage devices.
Memory representation: The units used to
measure computer memory are
Bit (b): The smallest unit of data on a machine
and can hold only 0 or 1
Byte(B): A unit of 8 bits is known as a byte.
It can contain any binary number between 00000000 &11111111
Kilobyte (KB): In binary system kilo refers to
1024 and a kilobyte is equal to 1024 bytes
Megabyte (MB): It comprises of 1024 kilobytes
and a megabyte can be thought of as a million bytes.
Gigabyte (GB): It consists of 1024 megabytes
and standard unit of measurement for hard disks.
Terabyte (TB): It refers to 1024 gigabytes and
usually associated with supercomputers.
Memory Hierarchy
1. Internal processor
memory: It is placed within the CPU and attached to special fast bus. It
includes cache memory and special registers which are directly accessed by the
processor. It is used for temporary storage of data and instructions on which
CPU is currently working. It the most expensive memory and fastest among all
the memories.
2. Primary memory:
Random Access Memory
(RAM): It allows the computer to store data for immediate manipulation and keep
track of what is currently being processed. It is the place in the where the
operating system, application programs and data in current use are kept and can
be accessed quickly by the computer’s processor. RAM is much faster to read
from and write to than the other kinds of storage. RAM is volatiles, ie., it
loses all its contents, when the computer is turned off. When the compute is turned on again, the
operating system and other files are once again loaded into RAM. When an
application program is started, the computer loads it into RAM and does all the
processing there.
Types of RAM:
ü Static RAM (SRAM)
ü Dynamic RAM (DRAM)
Read Only Memory (ROM): The data and
instructions stored in ROM can only be read and used but cannot be altered.
Every computer comes with a small amount of ROM, which contains the boot
firmware called BIOS. This holds enough information to enable the computer to
check its hardware and load its operating system into its RAM at the time of
system booting. It is non-volatile in nature, its contents are not lost when the
power is switched off.
Types of ROM
ü Masked ROM
ü Programmable ROM
(PROM)
ü Erasable Programmable
ROM (EPROM)
ü Electrically Erasable
Programmable ROM (EEPROM)
ü Flash ROM
1.
Secondary
memory (Auxiliary memory): It provides backup storage for instructions and data.
These are the least expensive and also have much larger storage capacity than
the primary memory. The commonly used Secondary memory devices are magnetic
disk and magnetic tapes.
Classification
of secondary storage devices
Sequential
access: Sequential access means the computer system searches the storage device
form the beginning until the desired data is found. The most common sequential
access storage device is magnetic tape where data is stored and processed
sequentially.
Magnetic
tape is like a plastic tape with a magnetic coating on it. The data is stored
in the form of tiny segments of magnetized and demagnetized portions on the
surface of the material. The tapes are an inexpensive and reliable storage
medium for taking backup.
Direct
access: Direct access, also known as random access, means that computer can go
directly to the location, where the data that the user wants, are stored. The
most common direct access storage devices are magnetic disk and optical disk.
Examples
of Secondary Storage Devices
Magnetic
disks are the most widely used and popular medium for direct access secondary
storage. They offer high storage capacity and reliability, and have the
capability to access the stored data directly. It consists of a plastic/metal
circular plate/platter, which is coated with a magnetic oxide layer. Data are
represented as magnetized spots on a disk. A magnetized spot represents 1 and
the absence of a magnetized spot represents 0.
Floppy
disk : It is round, flat piece of Mylar plastic, coated with ferric oxide,
encased in a protective plastic. It is a removable disk and is read and written
by floppy disk drive.
Hard
disk: It is the primary storage unit of the computer. It consist of a stack of disk platters that are made up
of aluminium alloy or glass substrate coated with a magnetic material and
protective layers. It plays a significant role in performance, storage
capacity, software support and reliability.
Optical
disk: It is a flat, circular, plastic disk coated with material on which bits
may be stored in the form of highly reflective areas and significantly less
reflective areas, from which the stored data may be read when illuminated with
a narrow beam of laser diode. These disks are capable of storing enormously high
amounts of data in a limited amount of space.
Memory
stick or Memory card is a digital storage device, which is designed to be used
with portable electronic devices such as mobile phones, digital cameras, PDAs,
iPod, etc.
Universal
Serial Bus (USB) developed by Intel, is
a set of connectivity specification that establishes communication between
personal computers and devices such as mouse, keyboard, pen drive, external
hard disk drives, etc.,
Input Output Media
Input
devices are used to provide data to the Central Processing Unit for processing.
After processing, the input data is converted into meaningful information and
this output is presented to the user with the help of output devices. An input
device is an electromechanical device that allows the user to feed information
into the computer for analysis, storage and to give commands to the computer.
An output device displays the processed information by converting into
graphical, alphanumeric, or audio-visual form. It can be displayed or viewed on
a monitor, printed on a printer, or listened through speakers. The printed form
of output is referred to as hard copy while the form of output displayed on the
screen is referred to as soft copy. Printers, plotters and microfilms are the
most commonly used hard copy output devices while monitors, voice response
systems, projectors, electronic whiteboards, headphones are some commonly used
soft copy output devices.
Importance
of Input/output devices
The processing of data by the computer system
can be viewed as a three-step process
Step
1 Data input via an input device
Step
2 Processing of data
Step
3 Data output via an output device
Examples
of input devices
Keyboard: It is the most common
data entry device. The keyboard is designed to resemble a regular typewriter
with a few additional keys with which an user can type text and commands.
Pointing devices are the input devices
by which a user can point or select items rapidly from the multiple options
displayed on the screen. These devices can also be used to create graphic
elements on the screen such as lines, curves and freehand shapes. The common
types of pointing devices include mouse, trackball, joysticks, touch screens
and light pens.
Speech recognition is the technology by
which sounds, words and phrases spoken by humans are converted into digital
signals, and these signals are transformed into coding patterns where the
meaning has been assigned.
Digital camera records images in a
electronic form and the image is represented in computer’s language of bits and
bytes.
Webcam is a portable video
camera, which captures live video or images that may be viewed in real time
over the network or the internet.
Scanner is a device that
scans an image and transforms the image ASCII (American Standard Code for
Information Interchange) codes. These images can be edited, manipulated,
combined and printed. The common types of scanners are handheld and flatbed.
Optical Character Recognition
(OCR)
software translates the bitmap image of text to ASCII codes that the computer
can interpret as letters, numbers and special characters.
Optical Mark
Recognition (OMR)
is the process of detecting the presence of intended marked responses. Optical
mark reading is done by a special device known as optical mark reader.
Magnetic Ink Character
Reader (MICR)
is used to recognize the magnetic ink characters, it reads the characters by
examining their shapes in a matrix form.
Bar
codes are machine-readable codes, represented in parallel vertical lines with
varying widths. By the combination of these vertical lines and pacing between
them, bar codes represent the alphanumeric data. Bar code data’s are read using
Bar code reader
Examples of output devices
Printers: A printer prints
information and data from the computer onto paper. The quality of printer is
determined by the clarity of a print it can produce, its resolution. Resolution
is used to describe the sharpness and clarity of an image. The higher the
resolution, the better is the image. Its measured in dpi(dots per inch). The
two basic categories of printers include Impact printers and Non-impact
printers. Impact printers work by physically striking a head or needle against
an ink ribbon to make a mark on the paper.
eg. Dot Matrix Printer, daisy wheel, Drum Printers and Non-impact
printers use techniques other than physically striking the page to transfer ink
onto the paper. eg. ink-jet and laser printers.
Plotters: They are
special-purpose drawing devices, which reproduce graphic images on paper using
a pen whose movements are controlled by the computer. Plotters are classified
as pen and electrostatic plotters.
Monitor: The monitor is the
most commonly used output device for producing soft-copy output. The two types
of monitors include Cathode Ray Tube (CRT) and Liquid Crystal Display (LCD).
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