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Memory Units

A memory unit is a fundamental part of a computer machine that performs a vital function for storing and
retrieving information and instructions. Memory units have distinct purposes, including primary and
secondary memories. In this article, we will delve into the concept of memory units, their kinds, functions,
and importance within the international field of computing.

Memory units are the lifeblood of computer structures. They offer the potential to store and get proper entry
to statistics, instructions, and packages, enabling computer structures to carry out a large variety of
obligations. In short, memory units are the digital brains of a PC or laptop, allowing it to systematize, hold,
and consider facts as desired. They are vital for the functioning of every hardware and software component of
a computer system, making them a vital part of any computing device.

Importance of Memory Units

o Speed: Memory units make it possible to store and retrieve instructions and data quickly, which
reduces processing instances and boosts overall system performance. This is crucial when handling
huge amounts of data or operating complicated programs.
o Temporary storage: Memory units serve as temporary storage for data and programs that are
currently in use, allowing users to quickly move between programs and files without waiting for data
to be loaded from a storage device.
o Multitasking: Memory units allow computer systems and different digital devices to do many tasks
simultaneously because they can store and retrieve data for multiple programs simultaneously.
o Reliability: Memory devices are extremely reliable because they're made to resist normal wear and
tear. They are a strong and reliable storage option because they are less vulnerable to damage from
outside forces like shock or vibration.
o Accessibility: Memory units are readily available and can be quickly updated or changed. This makes
increasing a system's memory capacity simple, enabling users to manage more data and execute
demanding programs.
o Energy efficiency: Memory units use less power than standard hard drives, resulting in lower heat
generation and reduced cooling requirements. This makes them more energy-efficient, specifically
crucial for devices like smartphones and laptops with limited battery life.

Types of memory units

Different kinds of memory units are utilized in computers, and each has its own purpose. Let's observe some
common types:

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1. RAM (Random access memory): RAM is like a quick and temporary workspace in your computer. It
stores data and programs that your computer is actively using. When you open a file or run the
software, it gets loaded into RAM, so your laptop can access it quickly. However, RAM is only
sometimes permanent storage, so everything in RAM is lost when you switch off your computer.
2. ROM (read-only memory): ROM is a memory that stores essential records that your laptop needs to
start up and run essential functions. It carries firmware or software programs. This is permanently
programmed into the computer's circuitry. The records in ROM cannot be modified, so it is secure and
reliable.
3. Cache Memory: Cache memory is a volatile memory used to store data or often accessed instructions.
Since the cache memory accesses data more quickly than RAM, this can enhance system performance.
Data can be accessed more quickly thanks to the greater proximity of cache memory to the CPU.
4. Virtual Memory: Virtual memory is a method of increasing available memory by utilizing hard drive
space. When RAM is at capacity, the computer temporarily transfers some data to the hard drive to
make room in RAM for different programs. This method enhances computer performance when
running numerous programs by allowing the machine to store more information than is feasible in
RAM.
5. Flash Memory: Flash memory is a non-volatile memory frequently appearing in solid-nation drives,
USB drives, and memory cards. It is extra reliable and faster than traditional hard drives, making it
appropriate for usage in devices that are portable. Transistors used in flash memory for data storage
remain current even if the power has been switched off.

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6. Registers: Registers are small, quick memory units found on the CPU. They can temporarily store
data during processing, like computation results or the content of certain memory addresses. Although
registers are the quickest type of memory currently accessible, their production costs are also the
highest.

Functions of Memory Units:

Memory devices serve numerous critical features in a computer device, and those capabilities are essential for
the overall operation and ordinary performance of the system.

o Data Storage: Memory devices offer storage for both transient and long-term facts. The primary
memory quickly holds statistics and commands while they're being actively used by the CPU, ensuring
that the computer can respond quickly to character input. Secondary memory serves as a long-term
garage answer, permitting customers to preserve files, set up software, and keep statistics that persist
even after the computer is turned off.
o Data Retrieval: Memory devices allow the computer system to retrieve records and commands
rapidly. Primary memory is, in particular, designed for quick record retrieval, offering the CPU the
essential sources to execute applications and carry out obligations successfully.
o Data Processing: The CPU uses number one memory as a workspace for information processing. It
masses statistics and commands from secondary memory into number-one memory for processing.
Once processing is complete, the results may be stored and returned to secondary memory, making an
allowance for fact modification and garage.
o Multitasking: Memory units play an important role in multitasking. They permit the computer system
to switch among distinctive packages and duties with the aid of storing and handling the facts and
instructions for everyone. With enough number-one memory, a computer can effortlessly cope with
multiple techniques simultaneously, enhancing productivity and customer enjoyment.
o System Performance: The amount and velocity of memory in a PC or laptop appreciably affect its
ordinary performance. A computer system with greater primary memory can manage huge and more
complex programs, leading to higher typical performance and faster reaction times. Additionally, the
entry speed of memory devices influences the PC's processing velocity, as quicker memory allows
faster information retrieval and execution of instructions.

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Measurements of memory units

Memory units are used to measure and represent data. These units, which can be measured in bits and bytes,
offer a technique to estimate the volume of data which can be stored in a specific device or system. Some of
the commonly used memory units are:

1. Bit: The computer memory units start from bit. A bit is the smallest memory unit to measure data
stored in main memory and storage devices. A bit can have only one binary value out of 0 and 1.
2. Byte: It is the fundamental unit to measure data. It contains 8 bits or is equal to 8 bits. Thus, a byte can
represent 2*8 or 256 values. They measure the size of files, documents, images, and other data types.
3. Kilobyte: A kilobyte contains 1024 bytes. It is frequently used to indicate data storage abilities and the
dimensions of small files. A small image or roughly 1024 characters of text can be stored in one
kilobyte. It frequently appears in spreadsheets, text documents, and small image files. Although
greater units of measurement have gained popularity as data files have grown in size, kilobytes are still
in use today.
4. Megabyte: A megabyte contains 1024 kilobytes. In comparison to a kilobyte, it represents more data.
Longer text pieces, high-resolution photos, and brief audio snippets can all fit into a megabyte. It is
frequently used for calculating the size of documents, software packages, and media files containing
songs and short films. Even though bigger units of measurement are being used more often due to the
expanding amount of data files, megabytes are still important and commonly utilized.
5. Gigabyte: A gigabyte contains 1024 megabyte. It has a considerable quantity of data storing capacity.
Larger files, such as high-definition films, entire photo albums, and software programs, can fit within a

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gigabit. Hard drives, solid-nation drives, and different types of data storage devices' storage capacities
are regularly measured using this technique. Gigabytes are a common unit of measurement in recent
times, particularly with the growth in the size of multimedia files and the demand for big amounts of
storage.
6. Terabyte: A terabyte contains 1024 gigabytes. It represents a huge quantity of data storage capacity.
Large databases, enormous video collections, and enterprise-level storage systems may all store a lot
of data in a terabyte. High-capacity external hard drives, cloud storage services, and data centers
frequently use it. Terabytes are becoming more and more significant as the need for large-scale data
processing and storage increases.
7. Petabyte: It represents a huge quantity of data storage capacity. Huge amounts of data, such as
important video libraries, huge databases, and enormous collections of high-resolution photographs,
can fit into a petabyte. It is frequently employed in data centers, cloud storage solutions, and data-
intensive scientific research.
8. Exabyte (EB): An exabyte contains 1024 petabytes. It has a huge quantity of storage capacity for
data. Large-scale data warehouses, worldwide internet traffic, and enormous video archives can be
stored in exabytes. Large-scale scientific simulations, cloud computing infrastructures, and enterprise-
level storage solutions all frequently rely on it.
9. Zettabyte (ZB): A zettabyte 1024 exabytes. It represents a data storing capacity that is nearly beyond
imagination. Mind-boggling amounts of data, such as global internet content, long-term Archival
storage, and thorough global data analysis, can be stored in zettabytes.
10. Yottabyte (YB): A yottabyte contains 1024 zettabytes. It represents an unbelievable volume of data
storage. A yottabyte may store unimaginable amounts of data, such as the equivalent of storing the
internet's content many times over or tracking enormous amounts of data from all available worldwide
sensors.

Central Processing Unit (CPU)


CPU [Central Processing Unit]. It is the brain of the computer. It is the part that does most of the work
in a computer system. Just like how our brain controls our body and processes information, the CPU carries
out instructions from programs and performs calculations. It’s made up of smaller components that work
together to execute tasks, making it the heart of any computing device.
All types of data processing operations from simple arithmetic to complex tasks and all the important
functions of a computer are performed by the CPU. It helps input and output devices to communicate with
each other and perform their respective operations. It also stores data which is input, intermediate results in

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between processing, and instructions. The CPU’s job is to make sure everything runs smoothly and
efficiently. In this article, we are going to discuss CPU in detail.

What is a CPU?
A Central Processing Unit is the most important component of a computer system. A CPU is hardware
that performs data input/output, processing, and storage functions for a computer system. A CPU can be
installed into a CPU socket. These sockets are generally located on the motherboard. CPU can perform
various data processing operations. CPU can store data, instructions, programs, and intermediate results.

History of CPU
Since 1823, when Baron Jons Jakob Berzelius discovered silicon, which is still the primary component used
in manufacturing CPUs today, the history of the CPU has experienced numerous significant turning points.
The first transistor was created by John Bardeen, Walter Brattain, and William Shockley in December 1947.
in 1958, the first working integrated circuit was built by Robert Noyce and Jack Kilby.
The Intel 4004 was the company’s first microprocessor, which it unveiled in 1971. Ted Hoff’s assistance was
needed for this. When Intel released its 8008 CPU in 1972, Intel 8086 in 1976, and Intel 8088 in June 1979, it
contributed to yet another win. The Motorola 68000, a 16/32-bit processor, was also released in 1979. The
Sun also unveiled the SPARC CPU in 1987. AMD unveiled the AM386 CPU series in March 1991.
In January 1999, Intel introduced the Celeron 366 MHZ and 400 MHz processors. AMD back in April 2005
with its first dual-core processor. Intel also introduced the Core 2 Dual processor in 2006. Intel released the
first Core i5 desktop processor with four cores in September 2009.
In January 2010, Intel released other processors like the Core 2 Quad processor Q9500, the first Core i3 and i5
mobile processors, and the first Core i3 and i5 desktop processors.
In June 2017, Intel released Core i9 desktop processor, and Intel introduced its first Core i9 mobile processor
In April 2018.

Different Parts of CPU

Now, the CPU consists of 3 major units, which are:
 Memory or Storage Unit
 Control Unit
 ALU(Arithmetic Logic Unit)
Let us now look at the block diagram of the computer:
Here, in this diagram, the three major components are also shown. So, let us discuss these major components
in detail.

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Memory or Storage Unit

As the name suggests this unit can store instructions, data, and intermediate results. The memory unit is
responsible for transferring information to other units of the computer when needed. It is also known as an
internal storage unit or the main memory or the primary storage or Random Access Memory (RAM) as all
these are storage devices.
Its size affects speed, power, and performance. There are two types of memory in the computer, which
are primary memory and secondary memory. Some main functions of memory units are listed below:
 Data and instructions are stored in memory units which are required for processing.
 It also stores the intermediate results of any calculation or task when they are in process.
 The final results of processing are stored in the memory units before these results are released to an output
device for giving the output to the user.
 All sorts of inputs and outputs are transmitted through the memory unit.

Control Unit
As the name suggests, a control unit controls the operations of all parts of the computer but it does not carry
out any data processing operations. Executing already stored instructions, It instructs the computer by using
the electrical signals to instruct the computer system. It takes instructions from the memory unit and then
decodes the instructions after that it executes those instructions. So, it controls the functioning of the
computer. Its main task is to maintain the flow of information across the processor. Some main functions of
the control unit are listed below:
 Controlling of data and transfer of data and instructions is done by the control unit among other parts of
the computer.
 The control unit is responsible for managing all the units of the computer.
 The main task of the control unit is to obtain the instructions or data that is input from the memory unit,
interpret them, and then direct the operation of the computer according to that.
 The control unit is responsible for communication with Input and output devices for the transfer of data or
results from memory.
 The control unit is not responsible for the processing of data or storing data.

ALU (Arithmetic Logic Unit)

ALU (Arithmetic Logic Unit) is responsible for performing arithmetic and logical functions or operations. It
consists of two subsections, which are:

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 Arithmetic Section: By arithmetic operations, we mean operations like addition, subtraction,

multiplication, and division, and all these operations and functions are performed by ALU. Also, all the
complex operations are done by making repetitive use of the mentioned operations by ALU.
 Logic Section: By Logical operations, we mean operations or functions like selecting, comparing,
matching, and merging the data, and all these are performed by ALU.
Note: The CPU may contain more than one ALU and it can be used for maintaining timers that help run the
computer system.

What Does a CPU Do?

The main function of a computer processor is to execute instructions and produce an output. CPU work
Fetch, Decode, and Execute are the fundamental functions of the computer.
 Fetch: the first CPU gets the instruction. That means binary numbers that are passed from RAM to
CPU.
 Decode: When the instruction is entered into the CPU, it needs to decode the instructions. with the help
of ALU(Arithmetic Logic Unit), the process of decoding begins.
 Execute: After the decode step the instructions are ready to execute.
 Store: After the execute step the instructions are ready to store in the memory.

Types of CPU
We have three different types of CPU:
 Single Core CPU: The oldest type of computer CPU is a single-core CPU. These CPUs were used in
the 1970s. these CPUs only have a single core that performs different operations. This means that
the single-core CPU can only process one operation at a single time. single-core CPU CPU is not
suitable for multitasking.
 Dual-Core CPU: Dual-Core CPUs contain a single Integrated Circuit with two cores. Each core has its
cache and controller. These controllers and cache work as a single unit. dual-core CPUs can work faster
than single-core processors.
 Quad-Core CPU: Quad-Core CPUs contain two dual-core processors present within a single integrated
circuit (IC) or chip. A quad-core processor contains a chip with four independent cores. These cores
read and execute various instructions provided by the CPU. Quad Core CPU increases the overall speed
of programs. Without even boosting the overall clock speed it results in higher performance.

Introduction to operating System and its Features

An operating system is the fundamental basis of all other application programs. Operating system is an
intermediary between the users and the hardware.

Operating system controls and coordinates the use of hardware among application programs. The major
services of an operating system are −

 Memory management
 Disk access
 Creating user interface

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 Managing the different programs operating parallel

 Likewise, it controls and manage the hardware’s working

Applications of Operating System

Following are the major applications of an operating system −

 An operating system is accountable for the formation and deletion of files and directories.
 An operating system manages the process of deletion, suspension, resumption, and synchronization.
 An operating system manages memory space by allocation and de-allocation.
 An operating system stores, organizes, and names and protects the existing files.
 Further, an operating system manages all the components and devices of the computers system
including modems, printers, plotters, etc.
 In case, if any device fails, the operating system detects and notify.
 An operating system protects from destruction as well as from unauthorized use.
 An operating system facilitates the interface to user and hardware.

Types of Operating System

Following are the major types of operating system −

 Disk Operating System (DOS)

 Windows Operating System
 Unix Operating System

Disk Operating System

MS-DOS is one of the oldest and widely used operating system. DOS is a set of computer programs, the
major functions of which are file management, allocation of system resources, providing essential features to
control hardware devices.

DOS commands can be typed in either upper case or lower case.

Features of DOS

Following are the significant features of DOS −

 It is a single user system.

 It controls program.
 It is machine independence.
 It manages (computer) files.
 It manages input and output system.
 It manages (computer) memory.
 It provides command processing facilities.
 It operates with Assembler.

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Types of DOS Commands

Following are the major types of DOS Command −

 Internal Commands − Commands such as DEL, COPY, TYPE, etc. are the internal commands that
remain stored in computer memory.
 External Commands − Commands like FORMAT, DISKCOPY, etc. are the external commands and
remain stored on the disk.

Windows Operating System

The operating system window is the extension of the disk operating system.

It is the most popular and simplest operating system; it can be used by any person who can read and
understand basic English, as it does not require any special training.

However, the Windows Operating System requires DOS to run the various application programs initially.
Because of this reason, DOS should be installed into the memory and then window can be executed.

Elements of Windows OS

Following are the significant element of Windows Operating System (WOS) −

 Graphical User Interface

 Icons (pictures, documents, application, program icons, etc.)
 Taskbar
 Start button
 Windows explorer
 Mouse button
 Hardware compatibility
 Software compatibility
 Help, etc.
Versions of Windows Operating System

Following are the different versions of Windows Operating System −

Version Year Version Year

Window 1.01 1985 Windows XP Professional x64 2005

Windows NT 3.1 1993 Windows Vista 2007

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Windows 95 1995 Windows 7 2009

Windows 98 1998 Windows 8 2012

Windows 2000 2000 Windows 10 2015

Windows ME 2000 Windows Server 2016 2016

Windows XP 2001

Unix Operating System

The Unix Operating System is the earliest operating system developed in 1970s. Let us consider the following
points relating to the Unix Operating System −

 It is an operating system that has multitasking features.

 It has multiuser computer operating systems.
 It runs practically on every sort of hardware and provides stimulus to the open source movement.
 It has comparative complex functionality and hence an untrained user cannot use it; only the one who
has taken training can use this system.
 Another drawback of this system is, it does not give notice or warn about the consequences of a user’s
action (whether user’s action is right or wrong).

Programming Language - Introduction

A programming language is a set of symbols, grammars and rules with the help of which one is able to
translate algorithms to programs that will be executed by the computer. The programmer communicates with
a machine using programming languages. Most of the programs have a highly structured set of rules. The
primary classifications of programming languages are:
 Machine Languages.
 Assembly Languages.
 High level Languages.

Machine Language
Machine language is a collection of binary digits or bits that the computer reads and interprets.
Machine language is the only language a computer is capable of understanding. Machine level language is a
language that supports the machine side of the programming or does not provide human side of the
programming. It consists of (binary) zeros and ones. Each instruction in a program is represented by a
numeric code, and numerical addresses are used throughout the program to refer to memory locations in the
computer’s memory. Microcode allows for the expression of some of the more powerful machine level
instructions in terms of a set of basic machine instructions.
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Assembly language
Assembly language is easier to use than machine language. An assembler is useful for detecting
programming errors. Programmers do not have the absolute address of data items. Assembly language
encourage modular programming

High level language

High level language is a language that supports the human and the application sides of the
programming. A language is a machine independent way to specify the sequence of operations necessary to
accomplish a task. A line in a high level language can execute powerful operations, and correspond to tens,
or hundreds, of instructions at the machine level. Consequently more programming is now done in high level
languages. Examples of high level languages are BASIC, FORTRAN etc

Compilation
The compiler program translates the instructions of a high level language to a machine level language.
A separate compiler is required for every high level language. High level language is simply a programmer’s
convenience and cannot be executed in their source. The actual high - level program is called a source
program. It is compiled (translated) to machine level language program called object program for that
machine by the compiler. Such compilers are called self resident compilers. Compiler compiles the full
program and reports the errors at the end

Compilation Process
The compilation and execution process of C can be divided in to multiple steps:
 Preprocessing Using a Preprocessor program to convert C source code in expanded source code.
"#include" and "#define" statements will be processed and replaced actually source codes in this step.
 Compilation Using a Compiler program to convert C expanded source to assembly source code.
 Assembly Using a Assembler program to convert assembly source code to object code.
 Linking Using a Linker program to convert object code to executable code. Multiple units of object
codes are linked to together in this step.
 Loading Using a Loader program to load the executable code into CPU for execution.

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Compilation Linking
 After all of the files are compiled, they must be "merged together" to produce a single
 executable file that the user use to run the program.
 In C, most compiled programs produce results only with the help of some standard programs, known
as library files that reside in the computer. This process is called linking.
 The result obtained after linking is called the executable file. The linker′s primary function is to bind
symbolic names to memory addresses.
 To do this, it first scans the files and concatenates the related file sections to form one large file. Then,
it makes a second pass on the resulting file to bind symbol names to real memory addresses.
 Loading is loading the executable into memory prior to execution
 There are two types of linking: Static linking. Dynamic linking.
 Static linking occurs at compilation time; hence it occurs prior to loading a program. With static
linking the external symbols that are used by the program (e.g. function names) are resolved at
compile time.
 Dynamic linking occurs at run time, so it occurs after or at the time of the loading of a program. With
dynamic linking the symbols are resolved either at loading time, or at run time when the symbol is
accessed (lazy binding).

Loading
 After the files are compiled and linked the executable file is loaded in the computer′s memory for
executing by the loader. This process is called Loading.
 Program loading is basically copying a program from secondary storage into main memory so it ′s
ready to run.
 In some cases, loading us just not copying the data from disk to memory, but also setting protection
bits, or arranging for virtual memory map virtual addresses to disk pages.

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List of Input Devices

Given below is the list of the most common input devices along with brief information about each of them.

1. Keyboard

 A simple device comprising keys and each key denotes either an alphabet, number or number
commands which can be given to a computer for various actions to be performed
 It has a modified version of typewriter keys
 The keyboard is an essential input device and computer and laptops both use keyboards to give
commands to the computer

2. Mouse

 It is also known as a pointing device

 Using mouse we can directly click on the various icons present on the system and open up various
files and programs
 A mouse comprises 3 buttons on the top and one trackball at the bottom which helps in selecting and
moving the mouse around, respectively
 In case of laptops, the touchpad is given as a replacement of the mouse which helps in the movement
of the mouse pointer

3. Joy Stick

 It is a device which comprises a stick which is attached at an angle to the base so that it can be moved
and controlled
 Mostly used to control the movement in video games
 Apart from a computer system, a joystick is also used in the cockpit of an aeroplane, wheelchairs,
cranes, trucks, etc. to operate them well

4. Light Pen

 It is a wand-like looking device which can directly be moved over the device’s screen
 It is light-sensitive
 Used in conjunction with computer’s cathode ray tube

5. Microphone

 Using a microphone, sound can be stored in a device in its digital form

 It converts sound into an electrical signal
 To record or reproduce a sound created using a microphone, it needs to be connected with an amplifier

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6. Scanner

 This device can scan images or text and convert it into a digital signal
 When we place any piece of a document on a scanner, it converts it into a digital signal and displays it
on the computer screen

7. Barcode Reader

 It is a kind of an optical scanner

 It can read bar codes
 A source of light is passed through a bar code, and its aspects and details are displayed on the screen
All the devices mentioned above are the most commonly used input devices. Several other such types of
equipment are used in different fields which can be counted as an input device.

List of Output Device

The commonly used output devices have been listed below with a brief summary of what their function is and
how they can be used.

1. Monitor

 The device which displays all the icons, text, images, etc. over a screen is called the Monitor
 When we ask the computer to perform an action, the result of that action is displayed on the monitor
 Various types of monitors have also been developed over the years

2. Printer

 A device which makes a copy of the pictorial or textual content, usually over a paper is called a printer
 For example, an author types the entire book on his/her computer and later gets a print out of it, which
is in the form of paper and is later published
 Multiple types of printers are also available in the market, which can serve different purposes

3. Speakers

 A device through which we can listen to a sound as an outcome of what we command a computer to
do is called a speaker
 Speakers are attached with a computer system and also are a hardware device which can be attached
separately
 With the advancement in technology, speakers are now available which are wireless and can be
connected using BlueTooth or other applications

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4. Projector

 An optical device which presents an image or moving images onto a projection screen is called a
projector
 Most commonly these projectors are used in auditoriums and movie theatres for the display of the
videos or lighting
 If a projector is connected to a computer, then the image/video displayed on the screen is the same as
the one displayed on the computer screen

5. Headphones

 They perform the same function as a speaker, the only difference is the frequency of sound
 Using speakers, the sound can be heard over a larger area and using headphones, the sound is only
audible to the person using them
 Also known as earphones or headset.

Operating System:
When you turn on a computer, it goes through several steps to prepare itself for Use. The first step is a
self-test .The computer identifies the devices that are attached to it counts the amount of memory available
and does a quick check to see whether the memory is functioning properly. This routine is initiated by apart of
the system software located in read –only memory a chip that contains brief permanent instructions for getting
the computer started. Operating system is a set of software that provides an interface between the machine and
the user. An Operating System not only provides an interface between the user and the hardware, but also
manages the memory, CPU, disks,
I-O management, and controls the execution of the programs. Operating System is a must for all computers
ranging from mainframes and supercomputers to small personal computers.
DOS Commands
DOS is nothing but one of the operating system. At the DOS prompt the user can enter a command. DOS
command can be classified into two categories.
1. INTERNAL DOS COMMANDS
2. EXTERNAL DOS COMMANDS

INTERNAL DOS COMMANDS are commands, which are used frequently and are stored in the Random
Access Memory of the computer. They are also referred to as MEMORY RESIDENT COMMANDS.

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EXTERNAL DOS COMMANDS are commands, which are used less frequently and are stored on the DOS
Diskette.
File organization under DOS:
DOS stores data on the secondary storage devices in the form of files. A file is a collection of data,
which has a certain unique name and occupies a certain amount of space (in bytes) on the disk. Each file is
differentiated from the other by the file name. Thus, not two file on the disk have the same filename.
There are some rules associated with naming of files. A file name has two parts
 The primary name
 Extension name.
The primary name can be a maximum of 8 character and the extension name can be a maximum of 3
Characters.

The DIR command

The DOS directory command is used to display a list of files on a diskette. This command is an internal
command.
Format : Dir
When the dir command is typed at the prompt it will display a list of the files contained on the default drive
along with the following information;
- the size of the file in “bytes”
- the data when information or instructions were last placed in the file.
- The time when information or instructions were last placed in the file.
Let us see an example:
C>dir <Enter>
Volume in drive A is DOS
Volume serial Number is 195E-79ec
COUNTRY SYS 17069 09-04-91 12:18
EGA SYS 4885 09-04-91 10:10a
FORMAT COM 14986 09-04-91 11:21
KEY COM 32911 09-04-91 1:30P
23434324 BYTES

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23434343433 BYTES FREE

The first 3 lines identifies the diskette in the A drive by printing its volume label and Volume serial
Number. The fourth line on words the directory listing follows.
The first column in the listing lists the filename. The second column lists the extension name. The third
column gives information on the size of the file in bytes. The fourth column gives the date of creation of the
file or the date when the file was last updated. The fifth column gives the time of file creation or last updation.
The last line tells how many files there are in the diskette and how many bytes of free or unused space there is
on the diskette.

The dir command is also used to display information on a single file.

For example:
C>dir format <enter>
Volume in drive A is DOS.
Volume serial number is 939e-343d
Directory of A:
FORMAT COM 32323 09-09-98 12:11 a
3434 BYTES
1 File(s)

DIR command with various options

Dir /w -This command displays the directory of a disk across the width of a screen.
Dir /p- /p stands for the pause mode
Dir *.* - lists all files with any primary name and any secondary name
Dir a*.*- lists all files starting with “a” in the primary name and any extension.
Dir *.- com lists all files with extension name “com”
Dir *.- Lists all files with no extension name.

CLS Command:
CLS command clears the screen and the DOS prompt is moved to the top of the screen
C>cls <enter>
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Copy Command:
COPY command is used to take another copy of a given file name.
Format:
C> copy <source file name > <destination file name >
Example:
C> copy text1.bas text2.bas
In the above example, the content of text.bas file will be copied into to text2.bas
in the same directory. Like wise files from one floppy to another floppy also can be done.

DEL Command:
Del command is used to delete a file or group of files in the floppy.
Format :
C > del <file name>
Example:
C> del text1.bas
The above command, will delete the file in the name of text1.bas.

REN command:
This command is used to change the file name.
Format:
C> REN <Source file name > <New file name >
Example:
C> Ren Text1.bas text10.bas
The above command changes the old file name text1.bas into to text10.bas

Creating & changing the Directories:

Using MD command new directory can be created
Format:
C> md <name of the directory>
Example:
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C> md basic
In the above example the MD command creates a directory in the name ‘basic’ Using RD command a
particular directory can be deleted. If there is no file in a directory then only the directory will be deleted.
Format:
C> rd <name of the directory to be deleted>

Example:
C> rd basic
In the above example the RD command removes a directory in the name of ‘basic’
Change directory:
By using CD command the current directory can be changed.
Example : C>cd basic
After execution of the above command the prompt will be in the following format
C/>BASIC>
External Commands:
The hard disk though its name makes it sound though some times can suffer a head crash. i.e, the read/write
collides with the platters destroying data. In such occasions all data on the disk is lost and irrecoverable. In
order to avoid this situation the utility called BACKUP is used.
Example 1:
B> Backup C: *.* A:
In the above case all files on the drive c are copied on to the diskette in drive A. All files present on the drive
A diskette are lost. If additional disk are required, BACKUP will ask for them.
Example 2:
C>Backup C:*.* A:/S
Will backup all files including those in sub directories (S option) onto the diskette in drive A:
Example 3:
C>Backup C:*.* A:/A
Can be used if you wish to add files to diskette on the A drive rather than replacing them.
Example 4:
C>Backup C:*.* A:/M
Will backup only those files, which have changed since the last backup Restore Command:
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The BACKUP command stores the files in a particular format, which can’t be retrieved through the copy
command. A special command called RESTORE is used for this purpose.
Example 1:
B> RESTORE A: C:TRY.*
Will restore from the diskette in drive A, all the files that have a filename of TRY and may have any
extension name.
Example 2:
C>RESTORE A: C:TRY.*/P
Gives you the option of being selective in choosing the files to be restored by prompting for each file only if
there is a change in the destination file. The changes can even be attributes of the file.
Example 3:
C>RESTORE A: C: /S
Will restore all files from the disk(s) in drive C, including all subdirectories and their files.
Disk comp Command :
It compares the contents of disk in the source drive and the disk in the target drive. DISKCOMP is a process
that is performed generally after a DISKCOPY command to check whether the DISKCOPY process has taken
place correctly or not.
DISK COMP performs a track by track comparison of the disks. It automatically determines the number of
sides and sectors per track based on the format of the source disk.
Format:”
DISKCOMP <DRILVE1:><DRIVE2:>
Example:
A> diskcomp a: b:<enter>

Format Command :
A brand new floppy diskette or hard disk cannot be used straight away. It has
to be prepared for use. The process of preparing a diskette for use by the computer is called FORMATTING.
FORMAT places an electronic road map on the diskette. Diskette can be used on the computer only after they
are formatted. The map contains directions to access the various parts of the floppy disk. The formatting
process
• sets up “information tracks” on a diskette which will store the data
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• Checks the quality of a diskette. If a defective are is discovered, the area in

“locked out” from use.
• Erase information which is previously stored (if any) on the disk.
Format:
A>FORMAT <DRIVE>
Example: A> FORMAT B: <ENTER>
The FORMAT command is also used to make a BOOTABLE FLOPPY also by transferring the operating
system files onto the floppy. This is done by using the option with the format command.

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