8/6/2019 Open Elective Notes
http://slidepdf.com/reader/full/open-elective-notes 1/19
BASIC COMPUTER OPERATIONS
A computer as shown in Fig performs basically five major operations or functions irrespective of their sizeand make. These are
1) it accepts data or instructions by way of input, 2) it stores data, 3) it can process data as required by the
user, 4) it gives results in the form of output, and 5) it controls all operations inside a computer. We
discuss below each of these operations.
1. Input: This is the process of entering data and programs in to the computer system. You should know
that computer is an electronic machine like any other machine which takes as inputs raw data and performs some processing giving out processed data. Therefore, the input unit takes data from us to the
computer in an organized manner for processing.
Fig.
2. Storage: The process of saving data and instructions permanently is known as storage. Data has to be
fed into the system before the actual processing starts. It is because the processing speed of CentralProcessing Unit (CPU) is so fast that the data has to be provided to CPU with the same speed. Therefore
the data is first stored in the storage unit for faster access and processing. This storage unit or the primarystorage of the computer system is designed to do the above functionality. It provides space for storing data
and instructions.
The storage unit performs the following major functions:
1 All data and instructions are stored here before and after processing.
2 Intermediate results of processing are also stored here.
3. Processing: The task of performing operations like arithmetic and logical operations is called
processing. The Central Processing Unit (CPU) takes data and instructions from the storage unit andmakes all sorts of calculations based on the instructions given and the type of data provided. It is then sent
back to the storage unit.
4. Output: This is the process of producing results from the data for getting useful information. Similarlythe output produced by the computer after processing must also be kept somewhere inside the computer
before being given to you in human readable form. Again the output is also stored inside the computer for
further processing.
1
8/6/2019 Open Elective Notes
http://slidepdf.com/reader/full/open-elective-notes 2/19
5. Control: The manner how instructions are executed and the above operations are performed.
Controlling of all operations like input, processing and output are performed by control unit. It takes careof step by step processing of all operations in side the computer.
2.4 FUNCTIONAL UNITS
In order to carry out the operations mentioned in the previous section the computer allocates the task
between its various functional units. The computer system is divided into three separate units for its
operation. They are 1) arithmetic logical unit, 2) control unit, and 3) central processing unit.
2.4.1 Arithmetic Logical Unit (ALU)
After you enter data through the input device it is stored in the primary storage unit. The actual processing
of the data and instruction are performed by Arithmetic Logical Unit. The major operations performed bythe ALU are addition, subtraction, multiplication, division, logic and comparison. Data is transferred to
ALU from storage unit when required. After processing the output is returned back to storage unit for
further processing or getting stored.
2.4.2 Control Unit (CU)
The next component of computer is the Control Unit, which acts like the supervisor seeing that things aredone in proper fashion. The control unit determines the sequence in which computer programs and
instructions are executed. Things like processing of programs stored in the main memory, interpretation of
the instructions and issuing of signals for other units of the computer to execute them. It also acts as aswitch board operator when several users access the computer simultaneously. Thereby it coordinates theactivities of computer’s peripheral equipment as they perform the input and output. Therefore it is the
manager of all operations mentioned in the previous section.
2.4.3 Central Processing Unit (CPU)
The ALU and the CU of a computer system are jointly known as the central processing unit. You may call
CPU as the brain of any computer system. It is just like brain that takes all major decisions, makes all sortsof calculations and directs different parts of the computer functions by activating and controlling the
operations.
FLOW CHART
A flowchart is a common type of diagram, that represents an algorithm or process, showing the
steps as boxes of various kinds, and their order by connecting these with arrows. This diagrammatic
representation can give a step-by-step solution to a given problem. Data is represented in these boxes, andarrows connecting them represent flow / direction of flow of data. Flowcharts are used in analyzing,
designing, documenting or managing a process or program in various fields.
A typical flowchart from older Computer Science textbooks may have the following kinds of
symbols:
Start and end symbolsRepresented as circles, ovals or rounded rectangles, usually containing the word "Start" or "End",
or another phrase signaling the start or end of a process, such as "submit enquiry" or "receive product".Arrows
Showing what's called "flow of control" in computer science. An arrow coming from one symbol
and ending at another symbol represents that control passes to the symbol the arrow points to.
Processing stepsRepresented as rectangles. Examples: "Add 1 to X"; "replace identified part"; "save changes" or
similar.
Input/OutputRepresented as a parallelogram. Examples: Get X from the user; display X.
2
8/6/2019 Open Elective Notes
http://slidepdf.com/reader/full/open-elective-notes 3/19
Conditional or decision
Represented as a diamond (rhombus). These typically contain a Yes/No question or True/Falsetest. This symbol is unique in that it has two arrows coming out of it, usually from the bottom point
and right point, one corresponding to Yes or True, and one corresponding to No or False. The
arrows should always be labeled. More than two arrows can be used, but this is normally a clear indicator that a complex decision is being taken, in which case it may need to be broken-down
further, or replaced with the "pre-defined process" symbol.
A number of other symbols that have less universal currency, such as:
• A Document represented as a rectangle with a wavy base;
• A Manual input represented by parallelogram, with the top irregularly sloping up from left to right.An example would be to signify data-entry from a form;
• A Manual operation represented by a trapezoid with the longest parallel side at the top, to
represent an operation or adjustment to process that can only be made manually.
• A Data File represented by a cylinder.
Flowcharts may contain other symbols, such as connectors, usually represented as circles, to represent
converging paths in the flowchart. Circles will have more than one arrow coming into them but only one
going out. Some flowcharts may just have an arrow point to another arrow instead. These are useful torepresent an iterative process (what in Computer Science is called a loop). A loop may, for example,
consist of a connector where control first enters, processing steps, a conditional with one arrow exiting the
loop, and one going back to the connector. Off-page connectors are often used to signify a connection to a(part of another) process held on another sheet or screen. It is important to remember to keep these
connections logical in order. All processes should flow from top to bottom and left to right.
3
8/6/2019 Open Elective Notes
http://slidepdf.com/reader/full/open-elective-notes 4/19
EX:-
4
8/6/2019 Open Elective Notes
http://slidepdf.com/reader/full/open-elective-notes 5/19
Characteristics of computer
Now-a-days computer is playing a main role in everyday life it has become the need of people just liketelevision, telephone or other electronic devices at home. It solves the human problems very quickly as
well as accuratly. The important characteristics of a computer are described below:
1. Speed
The computer is a very high speed electronic device. The operations on the data inside the computer are
performed through electronic circuits according to the given instructions. The data and instructions flowalong these circuits with high speed that is close to the speed of light. Computer can perform million of
billion of operations on the data in one second. The computer generates signals during the operation
process therefore the speed of computer is usually measure in mega hertz (MHz) or gega hertz (GHz). It
means million cycles units of frequency is hertz per second. Different computers have different speed.
2. Arithmetical and Logical Operations
A computer can perform arithmetical and logical operations. In arithmetic operations, it performs theaddition, subtraction, multiplication and division on the numeric data. In logical operation it compares the
numerical data as well as alphabetical data.
3. Accuracy
In addition to being very fast, computer is also very accurate device. it gives accurate output result
provided that the correct input data and set of instructions are given to the computer. It means that outputis totally depended on the given instructions and input data. If input data is in-correct then the resulting
output will be in-correct. In computer terminology it is known as garbage-in garbage-out.
4. Reliability
The electronic components in modern computer have very low failure rate. The modern computer can
perform very complicated calculations without creating any problem and produces consistent (reliable)
results. In general, computers are very reliable. Many personal computers have never needed a servicecall. Communications are also very reliable and generally available whenever needed.
5. Storage
A computer has internal storage (memory) as well as external or secondary storage. In secondary storage,
a large amount of data and programs (set of instructions) can be stored for future use. The stored data and
programs are available any time for processing. Similarly information downloaded from the internet can
be saved on the storage m
6. Retrieving data and programs
The data and program stored on the storage media can be retrieved very quickly for further processing. Itis also very important feature of a computer.
7. Automation
A computer can automatically perform operations without interfering the user during the operations. It
controls automatically different devices attached with the computer. It executes automatically the programinstructions one by one.
8. Versatility
5
8/6/2019 Open Elective Notes
http://slidepdf.com/reader/full/open-elective-notes 6/19
Versatile means flexible. Modern computer can perform different kind of tasks one by one of
simultaneously. It is the most important feature of computer. At one moment your are playing game oncomputer, the next moment you are composing and sending emails etc. In colleges and universities
computers are use to deliver lectures to the students. The talent of computer is dependent on the software.
9. Communications
Today computer is mostly used to exchange messages or data through computer networks all over the
world. For example the information can be received or send throug the internet with the help of computer.
It is most important feature of the modern information technology.
10. Diligence
A computer can continually work for hours without creating any error. It does not get tired while workingafter hours of work it performs the operations with the same accuracy as well as speed as the first one.
11. No Feelings
Computer is an electronic machine. It has no feelings. It detects objects on the basis of instructions given
to it. Based on our feelings, taste, knowledge and experience: we can make certain decisions and
judgments in our daily life. On the other hand, computer can not make such judgments on their own. Their judgments are totally based on instructions given to them.
12. Consistency
People often have difficulty to repeat their instructions again and again. For example, a lecturer feelsdifficulty to repeat a same lecture in a class room again and again. Computer can repeat actions
consistently (again and again) without loosing its concentration:
• To run a spell checker (built into a word processor) for checking spellings in a document.
• To play multimedia animations for training purposes.
• To deliver a lecture through computer in a class room etc.
A computer will carry out the activity with the same way every time. You can listen a lecture or performany action again and again.
13. PrecisionComputers are not only fast and consistent but they also perform operations very accurately and precisely.For example, in manual calculations and rounding fractional values (That is value with decimal point can
change the actual result). In computer however, you can keep the accuracy and precision upto the level,
you desire. The length calculations remain always accurate.
Classification of Computer
There are three main types of computers based on working.
Digital computer
Analog computer
Hybrid computer
Digital Computer:
A digital computer operates directly decimal digits that represent discrete data.
It takes input and gives output in the form of numbers.
It used for business and scientific and data processing.
It is useful for evaluating arithmetic expression and manipulation data.
6
8/6/2019 Open Elective Notes
http://slidepdf.com/reader/full/open-elective-notes 7/19
Analog computer:
Analog computer measures continuous electrical or physical magnitude like voltage, pressure etc,.
It accepts inputs which vary with time and intensity and directly applied to various devices.
The output from the system in the form graph reduced by plotting by pen or traced by cathode
tube.
Hybrid computer:
It is a combination of analog and digital computer. Hybrid computer is a digital computer that
accepts analog signals, converts them to digital and processes them in digital form. This integration isobtained by digital to analog and analog to digital converter. A hybrid computer may use or produce
analog data or digital data. It accepts a continuously varying input, which is then converted into a set of discrete values for digital processing.
Ex: In a hospital an intensive care unit (ICU) having analog devices may measure a patient heart function,temperature and other quantities. This measurement may convert into numbers and supplied to a digital
computer. This computer monitors gives the patients vital signs. It highlights the signals whenever an
abnormal detected.
Types of Computer (Based on Size)1. Main frame computer:
A main frame computer system is largest, fast operating and one of the most expensivecomputer systems.
These computers have word-length ranging form 32 bits to 64 bits.
They have large memory and support both multitasking and multi user capabilities.
They are capable of handling large number of peripherals (I/O devices).
The processing speed range in between 1 to 10 million instructions per second (MIPS).
This computer supports 100 users at a time.
The cost of this computer ranges from few lakhs to 50 lakhs of rupees.
The main frames are generally used to support wide database management system for
commercial applications. They are designed to handle complex scientific and engineering task.
2. Mini computer:
Mini computers are medium size, multi user computer system.
They are UNIX operating system to support 16 to 20 users at a time.
These are slower than main frame computer.
These computers have word length ranging form 8 bits to 32 bits.
The cost range from 50,000 to 1.5 lakhs.
Mini computers are suitable for research laboratories, small factories, engineering colleges.
They have the capacity of processing one million instructions per second. These are computers which support multi user capabilities.
They have more storage capacity compared to a micro computers
These are suitable for small scale business data processing and accounting problems.
3. Micro computer:
They have limited input, output capabilities little software and little storage capacity.
Early micro computer had word length of 8 bits. At presents micro computer had word
length 16 bit to 32 bit.
7
8/6/2019 Open Elective Notes
http://slidepdf.com/reader/full/open-elective-notes 8/19
Micro computer were first developed and introduced by IBM (International BusinessMachine) in the early 80’s. Due to their small size and commendable processing speed they were
given the name personal computer (PC).
They are cheap and easy to use.
Micro computer have a wide range of application.
These computers are used in general purpose calculation, home applications, commercial
applications, office automation.
4. Super computer:
Super computer are much faster and more powerful than main frame computers.
These computers have word length ranging form 64 bits to 96 bits.
A super computer contain a number of CPU’s which operate in parallel to make it faster.
They are used for solving very sophisticated problem.
They are also used in weapons, whether forecasting, research and development, automaticnuclear and plasma physics.
These are suitable for astrological computations, which involves complex mathematical
computations various assumptions and parameters.
Super computer have limited market because of their high cost.
Computer Generations:
We have five generations of computer and duration of each generation is around one decayed (10 Years).
First Generation (1940 – 1955)
Computer were extremely large, these computers typically used about 10 to 15 thousand vacuumtubes.
A vacuum tube has shorter life and limited reliability.
Large amount of heat produced by Vacuum tubes and they were bulky. These tubes consume lot of power while in operation.
Lot of space was required.
These computers had limited internal storage capacity and they were very slow.
These computer were program in machine language i.e., instructions to the computer were in the
form zero’s and one’s.
Punch cards were used to enter data into the computers.Ex: IBM-650
Second Generation (1956-1965)
Transistors made up of germanium semi-conductors as switching electronics device were used in thisgeneration.
Transistors were smaller, faster and more reliable.
Power consumption was less as compare to vacuum tubes.
Computers were smaller in size and occupied less space. These computers are cheaper than
vacuum tubes.
Magnetic core memories were used for internal storage.
Internal storage capacity of computer was increased to about 100k byte.
A no. of high level language were developed during this period. Ex: FORTAN, COBOL.
Ex: IBM-7090
Third Generation (1966-1975)
8
8/6/2019 Open Elective Notes
http://slidepdf.com/reader/full/open-elective-notes 9/19
These computers were built using integrated circuits. A IC is a circuit consisting of transistor, resistors and
capacitors assembled on a single chip on silicon.
Computers were built using both small scale integrated circuits (10 transistor/chip) and medium
scale IC’s (100 transistor/chip).
The size of internal storage (main memory) increased to 4 mega bytes.
Improved magnetic disk technology fully replaced magnetic tapes as secondary memory (external
memory).
Power consumption and size of a computer is reduced.
Multi-processing, Multi programming concepts are introduced.
Ex:- IBM-360/91
Fourth Generation (1976-1985)
Fourth generation of computers user microprocessors or a large scale IC that would perform variousfunctions like arithmetic, logical and other control operations.
Personal computers were introduced, cost of these computers become very less.
Interactive graphics I/O devices were developed. Networking computer system has been
introduced. Memory and size are reduced.
Ex : IBM PC.
Fifth Generation (1985 Onwards)
These computers are under development stage.
A chip contains million of components in a single IC’s.
The input and output information for these computers will be in the form of speech and graphic
images.
Computer will able to receive speech commands.
Computer will be able to see its surroundings.
Computers will use Intelligence software (Artificial Intelligence).
INPUT/OUTPUT DEVICES:
• The CPU of a microcomputer cannot do anything until it has data with which to work.
• All data that enters the CPU for processing originally comes from devices located outside the boxthat houses the CPU.
• These devices are called input devices because their function is to get data into the computer.
• Input devices can consist of such things as the keyboard, a floppy or hard disk, a mouse, another computer, or a laboratory instrument. Figure 6 illustrates some common input devices.
• In order to know what the CPU is doing, we must be able to view its operation.
• In order to do this, data must be sent out of the CPU to output devices.• These may consist of printers, plotters, and video monitors. Output can also be stored for later
viewing by sending it to floppy or hard disks.
• Data that are entered into the computer must be stored while waiting to be processed by the CPU.
• Data must also have someplace to go after being processed. The area of the computer that holdsdata is called the memory.
• All of the electronic and mechanical components of a microcomputer system are collectively
known as the hardware.
9
8/6/2019 Open Elective Notes
http://slidepdf.com/reader/full/open-elective-notes 10/19
In summary, a microcomputer (PC) consists of a central processing unit that accepts data from an input
device, processes the data, and then sends it to an output device. During the processing, data are stored inthe computer's memory. A typical microcomputer configuration is shown in below Figure 1.
Figure 1: Typical Microcomputer Hardware
When a microcomputer (PC) is first turned on, its memory is empty. Before it can begin processing any of your data, you must somehow get your data into the memory of the microcomputer.
The four most common methods of entering data into a computer are shown below.
1. Information is typed in from the keyboard.
2. Data are read in from secondary storage devices like floppy disks, hard disks, or tapedrives.
3. Data are collected and entered into the computer from interface devices such as analog-to-
digital converters.4. Information is entered into the computer from drawing or pointing devices such as a
digitizer (a type of drawing pad), a mouse, a joystick, or a scanner.
Most information that is processed by a computer originally gets into the computer by being typed in froma keyboard. Figure 2 is a diagram of a standard PC keyboard.
Figure 2: Standard PC Keyboard and QWERTY Keys
Early devices• Punched card
KEYBOARD:• The keyboard is divided into three sections.
• The main section looks much like a standard typewriter keyboard.
• It contains all the letters of the alphabet, standard punctuation symbols, the numbers zero through
nine, and several special purpose keys.• The arrangement of the keys in the main section is referred to as a QWERTY format, which
comes from the order of the first six keys in the second row.• The keys across the top are called special function keys (or just function keys). When you press a
function key depends on what software you are running.
• On the right side of the keyboard is the numeric keypad. The keys in this section are arranged like
those on a calculator and are designed to speed the entry of numeric data.
Types:
10
8/6/2019 Open Elective Notes
http://slidepdf.com/reader/full/open-elective-notes 11/19
Standard: Standard keyboards, such as the 101-key US traditional keyboard 104-key Windows
keyboards, include alphabetic characters, punctuation symbols, numbers and a variety of function keys. The internationally-common 102/105 key keyboards have a smaller 'left shift' key and an
additional key with some more symbols between that and the letter to its right (usually Z or Y).Gaming and multimedia: Keyboards with extra keys, such as multimedia keyboards, have special keys
for accessing music, web and other oft-used programs, a mute button, volume buttons or knob
and standby (sleep) button. Gaming keyboards have extra function keys, which can be
programmed with keystroke macros. For example, 'ctrl+shift+y' could be a keystroke that is
frequently used in a certain computer game. Shortcuts marked on color-coded keys are used for some software applications and for specialized for uses including word processing, video editing,
graphic design and audio editing.Thumb-sized: Smaller keyboards have been introduced for laptops, PDAs, cellphones or users who have a
limited workspace.
Numeric: Numeric keyboards contain only numbers, mathematical symbols for addition, subtraction,
multiplication, and division, a decimal point, and several function keys (e.g. End, Delete, etc.).They are often used to facilitate data entry with smaller keyboard-equipped laptops or with smaller
keyboards that do not have a numeric keypad.
MOUSE:
A pointing device is any human interface device that allows a user to input spatial data to a computer. Inthe case of mice and touch screens, this is usually achieved by detecting movement across a physical
surface. Analog devices, such as 3D mice, joysticks, or pointing sticks, function by reporting their angle of deflection. Movements of the pointing device are echoed on the screen by movements of the cursor ,
creating a simple, intuitive way to navigate a computer's GUI.
• Another popular input device is the mouse. A mouse is a device used to control the motion of the
cursor (the object on the screen that shows where the next user action will take place) on the video
display.• The outside and inside of a typical two-button mouse are shown in Figure 3.
Figure 3 A Typical PC Mouse
Imaging and Video input devicesVideo input devices are used to digitize images or video from the outside world into the computer. Theinformation can be stored in a multitude of formats depending on the user's requirement.
• Webcam
• Image scanner
• Fingerprint scanner • Barcode reader
• 3D scanner
• Laser rangefinder
11
8/6/2019 Open Elective Notes
http://slidepdf.com/reader/full/open-elective-notes 12/19
Audio input devicesIn the fashion of video devices, audio devices are used to either capture or create sound. In some cases, an
audio output device can be used as an input device, in order to capture produced sound.
• Microphone
• MIDI keyboard or other digital musical instrument
Visual Display UnitA visual display unit, often called simply a monitor or display, is a piece of electrical equipment which
displays images generated from the video output of devices such as computers, without producing a permanent record.
Most new monitors typically consist of a TFT LCD, with older monitors based around a cathode
ray tube (CRT). Almost all of the mainstream new monitors being sold on market now are LCD.
Screen Size: The size of a display is typically given as the distance between two opposite screen corners.
Ex: 15” (15 inches), 17” & 21”.
Imaging Techniques: As with television many different hardware technologies exist for displaying
computer-generated output:
• Liquid crystal display (LCD). TFT LCDs are the most popular display device for new computers.o Passive LCDs produce poor contrast, slow response, and other image defects. These were
used in most laptops until the mid 1990s.
o Thin Film Transistor LCDs give much better picture quality in several respects. Nearly all
modern LCD monitors are TFT.
• Cathode ray tube (CRT)
o Raster scans computer monitors, which produce images using pixels. These were the most
popular display device for older computers.
o Television sets were used by most early personal and home computers, connecting
composite video to the television set using a modulator . Resolution and image quality werestrongly limited by the display capabilities of television.
• Plasma display
• Video projectors use CRT, LCD or many other technologies to send light through the air to a
projection screen. Front projectors use screens as reflectors to send light back, while rear projectors use screens as diffusers to refract light forward. Rear projectors are often integrated into
the same case as their screen.
• Surface-conduction electron-emitter display (SED)
• Organic light-emitting diode (OLED) display
• Penetron military aircraft displays
Cathode Ray Tube (CRT):
A comparison of a 21" CRT TV monitor with a 17" CRT PC monitor
The CRT is the picture tube of a monitor. The back of the tube has a negatively charged cathode.
The electron gun shoots electrons down the tube and onto a charged screen. The screen is coated with a
pattern of phosphor dots that glow when struck by the electron stream. Each cluster of three dots, one of each color, is one pixel.
The image on the monitor's screen is usually made up from at least tens of thousands of such tiny
dots glowing on command from the computer. The closer together the pixels are, the sharper the image on
12
8/6/2019 Open Elective Notes
http://slidepdf.com/reader/full/open-elective-notes 13/19
screen can be. The distance between pixels on a computer monitor screen is called its dot pitch and is
measured in millimeters. Most monitors have a dot pitch of 0.28 mm or less.There are two electromagnets around the collar of the tube which deflect the electron beam. The
beam scans across the top of the monitor from left to right, is then blanked and moved back to the left-
hand side slightly below the previous trace (on the next scan line), scans across the second line and so onuntil the bottom right of the screen is reached. The beam is again blanked, and moved back to the top left
to start again. This process draws a complete picture, typically 50 to 100 times a second. The number of
times in one second that the electron gun redraws the entire image is called the refresh rate and is
measured in hertz (cycles per second). It is common in television or very early computer equipment, to usea technique called interlacing, in which all the odd-numbered lines of an image are traced, and then all the
even-numbered lines; the circuitry of such an interlaced display need be capable of only half the speed of
a non-interlaced display. An interlaced display, particularly at a relatively low refresh rate, can appear tosome observers to flicker , and may cause eyestrain.
Comparison:CRT
Advantages:
• Very high contrast ratio (20,000:1 or greater, much higher than many modern LCDs and plasmadisplays.)
• High speed response
• Excellent Additive color, wide gamut and low black level limited only by external environment.
• Can display natively in almost any resolution and refresh rate
• Near zero color, saturation, contrast or brightness distortion. Excellent viewing angle.
• No input lag
• A reliable, proven display technology.Disadvantages:
• Large size and weight (a 40" unit weighs over 200lbs)
• Geometric distortion in non-flat CRTs
• Older CRTs are prone to burn-in.
• Greater power consumption than similarly sized displays, such as LCD.
• Screened devices are prone to more effect at highest resolution (does not apply to triple-tube projection)
LCD
Advantages:
• Very compact and light
• Low power consumption
• No geometric distortion
Disadvantages:
• Low contrast ratio.
• Limited viewing angle. This causes color, saturation, contrast and brightness to vary, even within
the intended viewing angle from mere variations in posture.• Uneven backlighting in some monitors can cause brightness distortion, especially toward the
edges.
• Slow response times, which cause smearing and ghosting artifacts (although many modern LCDs
have response times of 8ms or less).
• Only has one native resolution. Displaying other resolutions requires a video scaler , which
degrades image quality at lower resolutions.
• Fixed bit depth, many cheaper LCDs are incapable of truecolor.
• Somewhat more expensive than CRT
13
8/6/2019 Open Elective Notes
http://slidepdf.com/reader/full/open-elective-notes 14/19
MEMORY SYSTEM IN A COMPUTER There are two kinds of computer memory: primary and secondary. Primary memory is accessible
directly by the processing unit. RAM is an example of primary memory. As soon as the computer is
switched off the contents of the primary memory is lost. You can store and retrieve data much faster with primary memory compared to secondary memory. Secondary memory such as floppy disks, magnetic
disk, etc., is located outside the computer. Primary memory is more expensive than secondary memory.
Because of this the size of primary memory is less than that of secondary memory. We will discuss aboutsecondary memory later on.
Computer memory is used to store two things: i) instructions to execute a program and ii) data. When the
computer is doing any job, the data that have to be processed are stored in the primary memory. This datamay come from an input device like keyboard or from a secondary storage device like a floppy disk.
As program or the set of instructions is kept in primary memory, the computer is able to follow instantlythe set of instructions. For example, when you book ticket from railway reservation counter, the computer
has to follow the same steps: take the request, check the availability of seats, calculate fare, wait for
money to be paid, store the reservation and get the ticket printed out. The programme containing these
steps is kept in memory of the computer and is followed for each request.
But inside the computer, the steps followed are quite different from what we see on the monitor or screen.
In computer’s memory both programs and data are stored in the binary form. You have already been
introduced with decimal number system, that is the numbers 1 to 9 and 0. The binary system has only twovalues 0 and 1. These are called bits. As human beings we all understand decimal system but the computer
can only understand binary system. It is because a large number of integrated circuits inside the computer
can be considered as switches, which can be made ON, or OFF. If a switch is ON it is considered 1 and if it is OFF it is 0. A number of switches in different states will give you a message like this: 110101....10.
So the computer takes input in the form of 0 and 1 and gives output in the form 0 and 1 only. Is it not
absurd if the computer gives outputs as 0’s & 1’s only? But you do not have to worry about. Everynumber in binary system can be converted to decimal system and vice versa; for example, 1010 meaning
decimal 10. Therefore it is the computer that takes information or data in decimal form from you, convert
it in to binary form, process it producing output in binary form and again convert the output to decimalform.
The primary memory as you know in the computer is in the form of IC’s (Integrated Circuits). These
circuits are called Random Access Memory (RAM). Each of RAM’s locations stores one byte of information. (One byte is equal to 8 bits). A bit is an acronym for binary digit , which stands for one binary
piece of information. This can be either 0 or 1. You will know more about RAM later. The Primary or internal storage section is made up of several small storage locations (ICs) called cells. Each of these cellscan store a fixed number of bits called word length.
Each cell has a unique number assigned to it called the address of the cell and it is used to identify the
cells. The address starts at 0 and goes up to (N-1). You should know that the memory is like a largecabinet containing as many drawers as there are addresses on memory. Each drawer contains a word and
the address is written on outside of the drawer.
Memory can be classified into two types
14
8/6/2019 Open Elective Notes
http://slidepdf.com/reader/full/open-elective-notes 15/19
Primary memory
Secondary memory
15
8/6/2019 Open Elective Notes
http://slidepdf.com/reader/full/open-elective-notes 16/19
Capacity of Primary Memory
You know that each cell of memory contains one character or 1 byte of data. So the capacity is defined in
terms of byte or words. Thus 64 kilobyte (KB) memory is capable of storing 64 _ 1024 = 32,768 bytes. (1
kilobyte is 1024 bytes). A memory size ranges from few kilobytes in small systems to several thousandkilobytes in large mainframe and super computer. In your personal computer you will find memory
capacity in the range of 64 KB, 4 MB, 8 MB and even 16 MB (MB = Million bytes).
The following terms related to memory of a computer are discussed below:
1. Random Access Memory (RAM): The primary storage is referred to as random access memory
(RAM) because it is possible to randomly select and use any location of the memory directly store and
retrieve data. It takes same time to any address of the memory as the first address. It is also calledread/write memory. The storage of data and instructions inside the primary storage is temporary. It
disappears from RAM as soon as the power to the computer is switched off. The memories, which
loose their content on failure of power supply, are known as volatile memories .So now we can saythat RAM is volatile memory.
2. Read Only Memory (ROM): There is another memory in computer, which is called Read Only
Memory (ROM). Again it is the ICs inside the PC that form the ROM. The storage of program anddata in the ROM is permanent. The ROM stores some standard processing programs supplied by the
manufacturers to operate the personal computer. The ROM can only be read by the CPU but it cannot
be changed. The basic input/output program is stored in the ROM that examines and initializes various
equipment attached to the PC when the switch is made ON. The memories, which do not loose their content on failure of power supply, are known as non-volatile memories. ROM is non-volatile
memory.
3. PROM There is another type of primary memory in computer, which is called Programmable ReadOnly Memory (PROM). You know that it is not possible to modify or erase programs stored in ROM,
but it is possible for you to store your program in PROM chip. Once the programmes are written it
cannot be changed and remain intact even if power is switched off. Therefore programs or instructionswritten in PROM or ROM cannot be erased or changed.
4. EPROM: This stands for Erasable Programmable Read Only Memory, which over come the problem
of PROM & ROM. EPROM chip can be programmed time and again by erasing the information stored
earlier in it. Information stored in EPROM exposing the chip for some time ultraviolet light and iterases chip is reprogrammed using a special programming facility. When the EPROM is in use
information can only be read.
5. Cache Memory: The speed of CPU is extremely high compared to the access time of main memory.Therefore the performance of CPU decreases due to the slow speed of main memory. To decrease the
mismatch in operating speed, a small memory chip is attached between CPU and Main memory whose
access time is very close to the processing speed of CPU. It is called CACHE memory. CACHEmemories are 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 each memory makes main
memory to be faster and larger than it really is. It is also very expensive to have bigger size of cachememory and its size is normally kept small.
6. Registers: The CPU processes data and instructions with high speed, there is also movement of data between various units of computer. It is necessary to transfer the processed data with high speed. So
the computer uses a number of special memory units called registers. They are not part of the mainmemory but they store data or information temporarily and pass it on as directed by the control unit.
SECONDARY/AUXILIARY MEMORY:
It is used as parentally data storage device.
Secondary memory access rate is slow.
16
8/6/2019 Open Elective Notes
http://slidepdf.com/reader/full/open-elective-notes 17/19
It stores system programs, data files, software, audio and video file.
Cost is less.
Information is stored here is first transferred to the main memory and then processed by the CPU.
Secondary memories are magnetic memory like magnetic tape, hard disc, floppy disc etc.,
17
8/6/2019 Open Elective Notes
http://slidepdf.com/reader/full/open-elective-notes 18/19
18
8/6/2019 Open Elective Notes
http://slidepdf.com/reader/full/open-elective-notes 19/19
Top Related