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COMPUTER DEFINITION:A computer is an electronic device, which executes software programs. It is made up of two parts - hardware and software . The computer processes input through input devices like mouse and keyboard. The computer displays output through output devices like a monitor and printer.
USES:
1. Word Processing - Word Processing software automatically corrects spelling and grammar mistakes. You can use the copy and paste features. You can print documents and make several copies. It is easier to read a word-processed document than a handwritten one. You can add images to your document.
2. Internet - It is a network of almost all the computers in the world. You can browse through much more information than you could do in a library. That is because computers can store enormous amounts of information.
3. Banks - All financial transactions are done by computer software.
They provide security, speed and convenience.
4. Travel - One can book air tickets or railway tickets and make hotel
reservations online.
5. Telecommunications - Software is widely used here. Also all mobile
phones have software embedded in them.
6. Defence - There is software embedded in almost every weapon.
Software is used for controlling the flight and targeting in ballistic
missiles. Software is used to control access to atomic bombs.
7. E-Learning - Instead of a book it is easier to learn from an E-learning
software.
CHARACTERISTICS :1. Speed : Computers work at an incredible speed. A powerful
computer is capable of performing about 3-4 million simple instructions per second.
2. Accuracy : In addition to being fast, computers are also accurate. Errors that may occur can almost always be attributed to human error
3. Diligence :Unlike human beings, computers are highly consistent. They do not suffer from human traits of boredom and tiredness resulting in lack of concentration. Computers, therefore, are better than human beings in performing voluminous and repetitive jobs.
4. Versatility :Computers are versatile machines and are capable of performing any task as long as it can be broken down into a series of logical steps. The presence of computers can be seen in almost every sphere – Railway/Air reservation, Banks, Hotels, Weather forecasting and many more.
5. No IQ: - Computer is a dumb machine and it cannot do any work without instruction from the user. It performs the instructions at tremendous speed and with accuracy.
Computer Classification: Computers can be generally classified
1. Personal computer: A small, single-user computer based on a
microprocessor. In addition to the microprocessor, a personal
computer has a keyboard for entering data, a monitor for
displaying information, and a storage device for saving data.
2. Workstation: A powerful, single-user computer. A workstation is
like a personal computer, but it has a more powerful
microprocessor and a higher-quality monitor.
3. Minicomputer: A multi-user computer capable of supporting from
10 to hundreds of users simultaneously.
4. Mainframe: A powerful multi-user computer capable of
supporting many hundreds or thousands of users simultaneously.
5. Supercomputer: An extremely fast computer that can perform
hundreds of millions of instructions per second.
Basic computer Operations:1. Input: This is the process of entering data and programs in to the
computer system. It 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.
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 Central
Processing 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.
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 and makes 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. Similarly the 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.
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 care of step by step
processing of all operations inside the computer.
FUNCTIONAL UNITS:The computer system is divided into three separate units for its operation. They
are :
1) arithmetic logical unit
2) control unit.
3) central processing unit.
Arithmetic Logical Unit (ALU) :
1. Logical Unit :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 by the
ALU are addition, subtraction, multiplication, division, logic and comparison. 2. Control Unit (CU) : The next component of computer is the Control Unit,which acts like the supervisor seeing that things are done in proper fashion.Control Unit is responsible for co coordinating various operations using timesignal. The control unit determines the sequence in which computer programsand instructions are executed
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 sorts of calculations and directs different parts of
the computer functions by activating and controlling the operations.
Computer basically consists of two parts:
1. Hardware
2. Software
Hardware:- Hardware refers to the physical devices of the computersystem. Thus the various input, output, storage, processing devicesconnected in a computer system constitute the hardware. Somecommon hardware devices are the monitor, the floppy disk drive, harddisk drive etc.
Software:To make the hardware work properly we require a set of
instructions. These set of instructions or programs which enhance
the capability of the computer machine is called software. Software
is a group of programs that solve specific problems. It acts as an
interface between the user and the hardware.
Types of software:
Software can be classified into two main categories:
1. The Application Software
2. the system Software
1.Application Software:- Application Software is a set of programsdesigned to solve specific functions of the user. The set of programsincluded in the application software packages are called applicationprograms and the programmers who prepare the applicationsoftware are called application software programmers.
It can be broadly classified into following categories:
1. Word processing software
2. Spreadsheet software
3. Database software
4. Graphics and presentation software
5. Entertainment and Educational software
6. Communication software
1. Word Processing Software: It is most widely used application
in the computer system to create, edit, view, store, retrieve and
print all kind of text based documents. The various documents
includes newspapers, magazines, letters and advertisements.
We can also bold, italic and underline a particular character
using this application software. Some commonly used word
processing softwares available are Microsoft Word, Word Pad
etc.
2. Spreadsheet Software: Spreadsheets are the applications that can hold
large amount of numerical data arranged in rows and columns. The
Spreadsheet software allows the user to prepare the computerized ledger. It
is used for financial results, maintain accounts etc.. Each box in which data
is entered is called cell. Different cells are combined to form a worksheet,
changes can also be made easily in each cell.
3.Database Software:- A database software is a set of programs
that can helps the user to create the database, maintains it by
performing modifications, organize it and relatively retrieve
useful information from it. It permits users to create and
maintain database to extract information from the database
whenever required.
4.Graphics and Presentation software :- It permits the users to
create charts, line drawing and graphically portray the data in
an electronic spreadsheet or database.
5.Communication software:- It permits users to send and
receive transmission of data to/from remote computers, and to
process and store the data as well.
2.)System Software:- The system software is a set of programs that
coordinate the operations of various hardware components connected to a
computer. It acts an interface between the user and the computer. The
programs that constitute the system software are called the system
programs and the people who prepare the system software are called
system programmers. Examples of system software are Operating system,
Compilers , Linkers , Assemblers and Interpreter.
Features:-
1.It allows the use of system programming.
2.Fast in speed.
3.It is machine dependent that is same system software cannot run on
different machine.
4.Smaller in size.
5.Difficult to design.
Operating System:-
An operating system is the program that, after being initially loaded into the
computer by a boot program, manages all the other programs in a computer. The other
programs are called applications or application programs. The application programs
make use of the operating system by making requests for services through a defined
application program interface (API). In addition, users can interact directly with the
operating system through a user interface such as a command language or a graphical
user interface (GUI)
USER
An operating system performs these services for applications:
1.)In a multitasking operating system where multiple programs can be running at the
same time, the operating system determines which applications should run in what
order and how much time should be allowed for each application before giving
another application a turn.
2.)It manages the sharing of internal memory among multiple applications.
3.)It handles input and output to and from attached hardware devices, such as hard
disks, printers, and dial-up ports.
o.s
HARDWARE
4.)It sends messages to each application or interactive user (or to a system
operator) about the status of operation and any errors that may have occurred.
5.)On computers that can provide parallel processing, an operating system can
manage how to divide the program so that it runs on more than one processor at a
time.
Linux, Windows 2000, OS/400 are all examples of operating systems.
Types:
1. Real-Time Systems:- A real-time operating system is a multitasking operating
system that aims at executing real-time applications.. The main objective of real-
time operating systems is their quick and predictable response to events. They
have an event-driven or time-sharing design and often aspects of both.
2.Multiuser :- A multi-user operating system allows multiple users to
access a computer system concurrently. Time-sharing system can be
classified as multi-user systems as they enable a multiple user access to
a computer through the sharing of time. Single-user operating systems,
as opposed to a multi-user operating system, are usable by a single user
at a time. Being able to have multiple accounts on a Windows
operating system does not make it a multi-user system.
3.Multitasking:- When only a single program is allowed to run at a
time, the system is grouped under a single-tasking system. However,
when the operating system allows the execution of multiple tasks at
one time, it is classified as a multi-tasking operating system. Multi-
tasking can be of two types: pre-emptive or co-operative. In pre-
emptive multitasking, the operating system slices the CPU time and
dedicates one slot to each of the programs. Unix-like operating systems
such as Solaris and Linux support pre-emptive multitasking.
4.Distributed:- A distributed operating system manages a group of
independent computers and makes them appear to be a single computer.
The development of networked computers that could be linked and
communicate with each other, gave rise to distributed computing.
Distributed computations are carried out on more than one machine.
When computers in a group work in cooperation, they make a
distributed system.
5. Embedded:- Embedded operating systems are designed to be used in
embedded computer systems. They are designed to operate on small
machines like PDAs with less autonomy. They are able to operate with
a limited number of resources. They are very compact and extremely
efficient by design. Windows CE and Minix 3 are some examples of
embedded operating systems.
Booting Process:-
Any computer becomes operational when some software takes
control of it. The process of starting or switching on the
computer is called booting of the computer. The disk with the
help of which the system boots itself is called bootable
diskand the program or set of instructions which help to
start the computer are called bootable programs.
There are mainly two types of booting:
1. Hot booting
2. Cold booting
1.Hot booting:-In this booting, we boot the system when the
computer halts or crashes due to some reasons by either pressing
the reset button or by pressing ctrl+alt+del keys simultaneously
from the keyboard. It is also known as resetting. On pressing the
restart button the computer restarts itself. If it doesn’t do so then
user should turn the power off, wait for few seconds, then again
switch on the power button and resume the operation.
2. Cold booting:-Switching on the computer by pressing ON/OFF
switch on the computer’s cabinet is known as cold booting. This
type startup is slow process and programs are loaded from the disk.
Programming LanguagesThere are two major types of programming languages. These are Low Level
Languages and High Level Languages. Low Level languages are further divided in to
Machine language and Assembly language.
Low Level Languages:- The term low level means closeness to the way in which the
machine has been built. Low level languages are machine oriented and require
extensive knowledge of computer hardware and its configuration.
(a) Machine Language:- Machine Language is the only language that is directly
understood by the computer. It does not needs any translator program. We also call it
machine code and it is written as strings of 1′s (one) and 0’s (zero). When this
sequence of codes is fed to the computer, it recognizes the codes and converts it in to
electrical signals needed to run it. For example, a program instruction may look like
this:
1011000111101
It is not an easy language for you to learn because of its difficult to understand. It is
efficient for the computer but very inefficient for programmers. It is considered to the
first generation language. It is also difficult to debug the program written in this
language.
Advantage:The only advantage is that program of machine language run very fast because no translation
program is required for the CPU.
Disadvantages:1.It is very difficult to program in machine language. The programmer has to know details of
hardware to write program.
2.The programmer has to remember a lot of codes to write a program which results in program
errors.
3.It is difficult to debug the program.
(b) Assembly Language:-It is the first step to improve the programming structure. You
should know that computer can handle numbers and letter. Therefore some combination of
letters can be used to substitute for number of machine codes.
The set of symbols and letters forms the Assembly Language and a translator program is
required to translate the Assembly Language to machine language. This translator program is
called `Assembler’. It is considered to be a second-generation language.
Advantages:1.The symbolic programming of Assembly Language is easier to understand and saves a lot of
time and effort of the programmer.
2.It is easier to correct errors and modify program instructions.
3.Assembly Language has the same efficiency of execution as the machine level language.
Because this is one-to-one translator between assembly language program and its
corresponding machine language program.
Disadvantages:
1.One of the major disadvantages is that assembly language is machine
dependent. A program written for one computer might not run in other
computers with different hardware configuration.
HIGH LEVEL LANGUAGES:-Higher level languages are simple
languages that use English and mathematical symbols like +, -, %, / etc. for its
program construction. Higher level languages are problem-oriented languages
because the instructions are suitable for solving a particular problem. For
example COBOL (Common Business Oriented Language) is mostly suitable
for business oriented language where there is very little processing and huge
output. There are mathematical oriented languages like FORTRAN (Formula
Translation) and BASIC (Beginners All-purpose Symbolic Instruction Code)
where very large processing is required.
Advantages :Higher level languages have a major advantage over machine
and assembly languages that higher level languages are easy to learn and use.
It is because that they are similar to the languages used by us in our day to
day life.
Assemblers
Assemblers performs the following functions:-
1.translate assembly instructions and pseudo-instructions
into machine instructions
2. Convert decimal numbers, etc. specified by
programmer into binary
Assemblers make two passes over the assembly file:-
a) First pass:- It reads each line and records labels in a
symbol table
b)Second pass:- It uses information in symbol table to produce
actual machine code for each line
Assembly Language
ProgramAssembler Machine Level Language
Program
INPUT OUTPUT
Linker
Linker is a tool that merges the object files produced by separate
compilation or assembly and creates an executable file
It performs the following tasks:-
1.Searches the program to find library routines used by program,
e.g. printf(), math routines.
2.Determines the memory locations that code from each module
will occupy and relocates its instructions by adjusting absolute
references.
Prog1.obj Prog2.obj Progn.obj
Linker
Executable Program File
Compilers
A compiler is a program that reads a program in one language, the
source language and translates into an equivalent program in another
language, the target language.
The translation process should also report the presence of errors in the
source program.
Source Program → Compiler → Target Program
↓
Error Messages
There are two parts of compilation:-
1.)The analysis part breaks up the source program into constant piece
and creates an intermediate representation of the source program.
2.)The synthesis part constructs the desired target program from the
intermediate representation.
LoaderA loader is the part of an operating system that is responsible for loading
programs. It is one of the essential stages in the process of starting a program,
as it places programs into memory and prepares them for execution. Loading
a program involves reading the contents of executable file, the file containing
the program text, into memory, and then carrying out other required
preparatory tasks to prepare the executable for running. Once loading is
complete, the operating system starts the program by passing control to the
loaded program code.
All operating systems that support program loading have loaders, apart from
systems where code executes directly from ROM or in the case of highly
specialized computer systems that only have a fixed set of specialised
programs.
In the case of operating systems that support virtual memory, the loader may
not actually copy the contents of executable files into memory, but rather may
simply declare to the virtual memory subsystem that there is a mapping
between a region of memory allocated to contain the running program's code
and the contents of the associated executable file.
Computer Memory
DEFINITION:-Memory is something that stores, preserves and recalls data
when needed. Computer memory stores data that is accessed by the Central
Processing Unit (CPU). Thus, memory acts as storage for uncompleted tasks and
other information needed to accomplish those tasks.
TYPES OF MEMORY:-
1) RAM (Random-Access Memory): This is the same as main memory. When
used by itself, the term RAM refers to read and write memory; that is, you can
both write data into RAM and read data from RAM. This is in contrast to ROM,
which permits you only to read data. Most RAM is volatile, which means that it
requires a steady flow of electricity to maintain its contents. As soon as the
power is turned off, whatever data was in RAM is lost.
TYPES OF RAM:
1. Dynamic RAM (DRAM): Most computers incorporate two types of
volatile RAM: static and dynamic. Although both types require constant
electrical current to function, they have some important differences.
Dynamic RAM is less expensive, and therefore it is the most widely used.
DRAM stores each bit of information in a separate capacitor on the
integrated circuit. The DRAM chip requires only one transistor and one
capacitor for each bit of storage. This makes it both cheap and space
efficient. DRAM also suffers periodic access limitations, because it
cannot be read during the refresh cycle. One specialized type of DRAM
is more common is embedded DRAM, or EDRAM.EDRAM is DRAM
integrated onto the same chip as the processor and used as cache memory.
2. Static RAM (SRAM): Static RAM (SRAM) has the advantage of
being faster than DRAM, although the disadvantage is that it is more
expensive.
SRAM generally requires less power than DRAM, although its
power requirements vary depending on clock speed. At higher
clock speeds, it can use as much power as DRAM; however, at
more moderate speeds, it requires only a fraction of what DRAM
uses. When idle, SRAM power requirements are low. Each bit in a
SRAM chip requires a cell of six transistors, although DRAM
needs only one transistor and one capacitor. This means that
SRAM cannot achieve the storage densities of the DRAM family.
As with DRAM, SRAM chips are mostly large arrays of these cells
of transistors. The two primary applications of SRAM are
1. Embedded use and in computers. Embedded use refers to
SRAM use in automotive and consumer electronics, industrial
equipment, and almost all appliances or toys with an electronic
user interface.
2. Devices, such as cell phones and music synthesizers, can
incorporate several megabytes of SRAM.
2)ROM (read-only memory): Computers almost always
contain a small amount of read-only memory that holds
instructions for starting up the computer. Unlike RAM, ROM
cannot be written to.
TYPES OF ROM:1) PROM(programmable read-only memory): A PROM is a
memory chip on which you can store a program. But once the
PROM has been used, you cannot wipe it clean and use it to store
something else. Like ROMs, PROMs are non-volatile.
2) EPROM(erasable programmable read-only memory): An
EPROM is a special type of PROM that can be erased by
exposing it to ultraviolet light.
3)EEPROM(electrically erasable programmable read-only
memory): An EEPROM is a special type of PROM that can be
erased by exposing it to an electrical charge.
CACHE MEMORY:
Cache memory is random access memory (RAM )that a
computer microprocessor can access more quickly than it can
access regular RAM. As the microprocessor processes data, it
looks first in the cache memory and if it finds the data there
(from a previous reading of data), it does not have to do the more
time-consuming reading of data from larger memory.
Cache that is built into the CPU is faster than separate cache,
running at the speed of the microprocessor itself. However,
separate cache is still roughly twice as fast as Random Access
Memory (RAM). Cache is more expensive than RAM, but it is
well worth getting a CPU and motherboard with built-in cache in
order to maximize system performance.
Disk caching applies the same principle to the hard disk that memory
caching applies to the CPU. Frequently accessed hard disk data is
stored in a separate segment of RAM in order to avoid having to
retrieve it from the hard disk over and over. In this case, RAM is faster
than the platter technology used in conventional hard disks.
Main Memory
(RAM)
Cache
Memory
Processor(CPU)
SECONDARY STORAGE DEVICES
The primary memory stores all the information in the form of electric
signals. So whenever power fails or you switch off the computer all the
information that has been stored is lost. Therefore there was requirement of
some other memory medium where large data and information can be stored
permanently. This requirement of memory generated the secondary storage
devices or Secondary Memory of the computers. The Secondary Memory is
also known as Auxiliary Memory or Backup Memory.
TYPES OF SECONDARY STORAGE DEVICES:
i) Floppy disk
ii) Hard disk
iii) CDROM
iv) Magnetic tape
v) DVD
i) Floppy Disk: A floppy disk is a secondary storage device. It is a
circular piece of plastic material coated with particles, which are
magnetized. This thin plastic sheet is protected from outside by a plastic
cover to prevent the sensitive data stored on them. The commonly used
floppy disks are of 3.5 ” diameter. Floppies are used to store data and
transfer them from one computer to another. Due to their size and portability
they are the most popular storage mediums in offices and at homes.
The data inside the floppies are stored in tracks and sectors. The entire
floppy is divided into circular segments called tracks. Each track is given a
unique number. The outermost track is referred as 0 and the track inner to
them is 1 and so on. Each track is further divided into segments called
sectors. The number of segments in each track has the same capacity. In a
typical 3.5” floppy disk the number of tracks and sectors and their storage
capacity is denoted below:
1.44 MB = 1.474560 bytes = 512 bytes X 2 sides
ii) HARD DISKS: A hard disk is fixed inside the cabinet of CPU (Central
Processing Unit). It is made up of many rigid metal platters coated to store
data magnetically. The hard disk rotates while recording data. This rotation
speed is measured in the unit of revolutions per minute (rpm). The normal
speed of hard disks is 3600 revolutions per second. The read/write head of
the hard disks moves across its surface. The storage capacity of the hard
disks is many times more than the floppy disks.
The normal storage capacity of hard disks installed inside the Pentium-IV
machines now a day is 40 Gigabytes. Due to large storage capacity it is
preferred to store all important data into the hard disks of the computers.
The data stored in the hard disks are retrieved faster as compared to the
floppy disks as they are installed inside the computers.
diskDisk head
iii) CD-ROM (COMPACT DISK READ ONLY MEMORY)
Compact Disks most popularly known as CDs are the most attractive
storage device these days. They are Read only memory device as without
the CD writers we cannot store our files and folders on them. The diameter
of the CD ranges from 10 cms to 30 cms. A typical CD is of 13 cm diameter.
One CD can store 600 MB to 750 MB data on it. Laser reads the normally
used CDs. So once the data is stored into the CD ROM it cannot be erased.
Recently writable CDs are also introduced in the market but they are not so
common. The read/write speed of a CD-ROM is average access tune is 125
milliseconds.
CD comprises of a transparent thin layer of aluminium covering the pitted
surface for reflectivity. The data may be in the form of text, image, sound,
video clips, animated movies or their combinations. The CD Rom drive are
mostly used to keep back ups & access the data for reading.
iv) Magnetic Tape: Magnetic Tape is a recording medium consisting of
a thin tape with a coating of a fine magnetic material, used for recording
analogue or digital data. A device that stores computer data on magnetic
tape is a tape drive. The capacity of tape media are generally on the same
order as hard disk drives . Magnetic Tapes Generally transfer data a bit
slower than hard drives, however magnetic tapes are cheaper and are more
durable
Organization of data on disks:
I)TRACKS: A circle on the disk surface on which data are contained.
II)SECTORS:1. That portion of a track falling along a predefined pie-shaped portion of
the disk surface.
2. The number of bytes stored in a sector is the same, regardless of where
the sector is located; thus, the density of bits is greater for sectors near the
centre of the disk
3. The rotational speed is constant; i.e., constant angular velocity
4. Thus, the transfer rate is the same for inner sectors and outer sectors
III) CYLINDERS: A set of tracks simultaneously accessible from the
heads on the head assembly.
IV) HEADS:A transducer attached to an arm for writing/reading data
to/from the disk surface
Head assembly: A mechanical unit holding the heads and arms. All the
head/arm units move together, via the head assembly
42Figure 11.1 Moving-head disk mechanism (HDD)
Access time : The access time or response time of a rotating drive is
a measure of the time it takes before the drive can actually transfer data. The
factors that control this time on a rotating drive are mostly related to the
mechanical nature of the rotating disks and moving heads. It is composed of
a few independently measurable elements that are added together to get a
single value when evaluating the performance of a storage device. The key
components that are typically added together to obtain the access time are:
1. Seek time
2. Latency time
1. Seek Time: The seek time measures the time it takes the head assembly
on the actuator arm to travel to the track of the disk where the data will be
read or written.[7] The data on the media is stored in sectors which are
arranged in parallel circular tracks and there is an actuator with an arm that
suspends a head that can transfer data with that media. When the drive needs
to read or write a certain sector it determines in which track the sector is
located.
It then uses the actuator to move the head to that particular track. If the
initial location of the head was the desired track then the seek time would be
zero. If the initial track was the outermost edge of the media and the desired
track was at the innermost edge then the seek time would be the maximum
for that drive.
2. Latency Time: It is the delay waiting for the rotation of the disk to bring the required disk sector under the read-write head. It depends on the rotational speed of a disk , measured in revolutions per minute (RPM).For most magnetic media-based drives, the average rotational latency is typically based on the empirical relation that the average latency in milliseconds for such a drive is one-half the rotational period. Maximum rotational latency is the time it takes to do a full rotation excluding any spin-up time . Therefore the rotational latency and resulting access time can be improved (decreased) by increasing the rotational speed of the disks.
45
Seek Time Latency Time Transfer Rate
Desired
track
Seek
Head
TransferLatency
Note: Access time = seek time + latency