How Will I Use an Operating System?

The user interface of an operating system is the portion of the program with which users interact.
The user interface can be

1. Command-line,
2.Menu-driven, and
3.Graphics-based.

A command-line interface requires a user to type the desired response at a prompt using a special command language.

To be an effective user of any command-line software, you must memorize its commands and their exact syntax-no easy task.

A menu-driven interface allows the user to select commands from a list (menu) using the keyboard or a pointing device such as a mouse.

A graphical user interface (GUI):

The trend is away from text-based, command-line interfaces to user-friendly, graphics-oriented environment called a graphical user interface (GUI).

Graphical user interfaces rely on graphics-based software.

Graphic-based software permits the integration of text with high-resolution graphic
image, called icons.

GUI users interact with the operating system and other software packages by using a pointing device and a keyboard to issue commands.

Rather than enter a command directly, the user chooses from options displayed on the screen.

The equivalent of a syntax-sensitive operating system command is entered by pointing to and choosing one or more options from menu or by pointing to and choosing a graphics image, called an icon.

Typically GUI includes some or all of the following parts:

-Icons, which are graphical images that represent items, such as files and directories.
-Agraphical pointer, which is controlled by a pointing device (mouse), to select icons and
commands and move on-screen items.
-On-screen pull-down menus that appear or disappear, controlled by the pointing device.
-Windows that enclose applications or objects on the screen.

GUIs have effectively eliminated the need for users to memorize and enter cumbersome commands.

Type of Processing

A multiprocessing operating system allows the simultaneous execution of programs by a computer that has two or more CPUs. Each CPU can be either dedicated to one program, or dedicated to specific functions and then used by all programs.

Interprocessing, also called dynamic linking, is a type of processing that allows any change made in one application to be automatically reflected in any related, linked application.

Real-time processing allows a computer to control or monitor the performance of other machines and people by responding to input data in a specified amount of time.

Virtual-machine (VM) processing creates the illusion that there is more than one physical machine. VM capabilities permit a computer to run numerous operating systems at one time. VM capabilities are typically used on supercomputers and mainframes.

Virtual memory, also called virtual storage, allows you to use a secondary-storage device as an extension of main memory. Virtual memory resolves the problem of insufficient main memory to contain an entire program and its data.

Major Functions of Operating Systems

The major functions of an OS are:

-resource management,
-data management,
-job (task) management, and
-standard means of communication between user and computer.

The resource management function of an OS allocates computer resources such as CPU time, main memory, secondary storage, and input and output devices for use.

The data management functions of an OS govern the input and output of the data and their location, storage, and retrieval.

The job management function of an OS prepares, schedules, controls, and monitors jobs submitted for execution to ensure the most efficient processing. A job is a collection of one or more related programs and their data.

A job is a collection of one or more related programs and their data.

The OS establishes a standard means of communication between users and their computer systems. It does this by providing a user interface and a standard set of commands that control the hardware.

Typical Day-to-Day Uses of an Operating System

-Executing application programs.
-Formatting floppy diskettes.
-Setting up directories to organize your files.
-Displaying a list of files stored on a particular disk.
-Verifying that there is enough room on a disk to save a file.
-Protecting and backing up your files by copying them to other disks for safekeeping.

How Do Operating Systems Differ?

Operating systems for large computers are more complex and sophisticated than those for microcomputers because the operating systems for large computers must address the needs of a very large number of users, application programs, and hardware devices, as well as supply a host of administrative and security features.

Operating system capabilities can be described in terms of

-the number of users they can accommodate at one time,
-how many tasks can be run at one time, and
-how they process those tasks.

Number of Users:

A single-user operating system allows only one user at a time to access a computer.

Most operating systems on microcomputers, such as DOS and Window 95, are single-user access systems.

A multiuser operating system allows two or more users to access a computer at the same time (UNIX).

The actual number of users depends on the hardware and the OS design.
Time sharing allows many users to access a single computer.
This capability is typically found on large computer operating systems where many users need access at the same time.

Number of Tasks

An operating system can be designed for single tasking or multitasking.

A single tasking operating system allows only one program to execute at a time, and the program must finish executing completely before the next program can begin.

A multitasking operating system allows a single CPU to execute what appears to be more than one program at a time.

Context switching allows several programs to reside in memory but only one to be active at a time. The active program is said to be in the foreground. The other programs in memory are not active and are said to be in the background. Instead of having to quit a program and load another, you can simply switch the active program in the foreground to the background and bring a program from the background into the foreground with a few keystrokes.

Cooperative multitasking in which a background program uses the CPU during idle time of the foreground program. For example, the background program might sort data while the foreground program waits for a keystroke.

Time-slice multitasking enables a CPU to switch its attention between the requested tasks of two or more programs. Each task receives the attention of the CPU for a fraction of a second before the CPU moves on to the next. Depending on the application, the order in which tasks receive CPU attention may be determined sequentially (first come first served) or by previously defined priority levels.

Multithreading supports several simultaneous tasks within the same application. For example, with only one copy of a database management system in memory, one database file can be sorted while data is simultaneously entered into another database file.

Operating System

What Is an Operating System?

An operating system (OS) is a core set of programs that control and supervise the hardware resources of a computer and provide services to other system software, application software, programmers, and users of a computer.

The OS gives the computer the instructions it needs to operate, telling it how to interact with hardware, other software, and the user.

The OS establishes a standard interface, or means of communication, between users and their computer systems.
When you power up a computer, you boot the system.
The booting procedure is so named because the computer "pulls itself up by its own bootstraps" (without the assistance of humans).
When booting the system,

First, a program in read-only memory (ROM) initializes the system and runs a system check to verify that the electronic components are operational and readies the computer for processing.
Next, the operating system is loaded to RAM, takes control of the system, and presents the user with a system prompt or a GUI screen full of options.

Operating System Parts

Operating systems are composed of two major parts:

control programs, and
service program.

Control programs manage computer hardware and resources.
The main program in most operating systems is the supervisor program.

A supervisor program is a control program that is known in some operating systems as the monitor, executive, or kernel.
The supervisor program is responsible for controlling all other OS programs as well as other system and application programs.
The supervisor program controls the activities of all of the hardware components of a computer.


Service programs are external OS programs that provides a service to the user or programmer of a computer.
They must be loaded separately because they are not automatically loaded when the operating system is loaded.
They perform routine but essential functions, such as formatting a disk for use and copying files from one location to another.

Computer language-oriented software includes

language translators such as assemblers, interpreters, and compilers.

Program generators (programs that automatically generate program code), debugging and testing programs.

Utilities are programs that are purchased as separate products; they perform a wide range of functions. This type of software includes products such as

-data conversion programs that convert data from one format to another,
-data recovery programs that restore damaged or accidentally erased data,
-librarians that log and track the locations of disk or tape program files,

-security and auditing programs, and

-merge and sort programs.

Application software refers to programs that allow you to accomplish specific tasks, like creating a document, organizing data, or drawing graphs.

Software acts as a connection, or interface, between you and the hardware.

-Interface is a term that describes how two parts are joined so that they can work together.

-System software and application software provide an interface to the hardware.

Shows the functional relationship among system software, application software, hardware, and a user.

Categories of Software

Knowledge the Rooms in the House

Computer hardware cannot perform alone.

Software refers to the instructions that direct the operations of a computer.

There are two basic types of software:

-system software (controls hardware), and
-application software (performs specific tasks).

System software refers to programs designed to perform tasks associated with directly controlling and utilizing computer hardware.

-It does not accomplish specific tasks for a user, such as creating documents or analyzing data.

-System software includes:

-Operating systems (the most important type of system software),
-Data management software,
-Computer language-oriented software, and
-Utilities that help users perform various functions.

-Data management software includes:

-database and file management programs that manage data for an operating system.
-data center management programs used on large system computers that control program execution, monitor system usage, track system resources and utilization, and bill users accordingly.

Interactive With The System

To interact effectively with a computer, user needs to be knowledgeable in four areas.

1.General software concepts (for example, windows, menus, uploading, and so on)

2.The operation and use of the hardware over which you have control (such as the PC, magnetic
disk, and printer).

3.The function and use of the computer's operating system and/or its graphical user interface
(GUI), both of which provide a link between the user, the computer system, and the various
applications.

4.The specific applications programs you are using

The first three areas are prerequisites to the fourth because you will need a:

• working knowledge of software concepts,
  
• hardware, and
  
• the operating system and/or a GUI
  

before you can make effective use of

• Quicken (accounting),
  
• Harvard Graphics (presentation graphics),
  
• Paradox (database).

COMMUNICATION AND NETWORK CONCEPTS

Evolution of Networking: ARPANET, Internet, Interspace.

Different ways of sending data across the network with reference to switchingtechniques.

Data Communication terminologies: Concept of Channel, Baud, Bandwidth (Hz, KHz, MHz) and Data transfer rate (bps, kbps, Mbps, Gbps, Tbps).

Transmission media: Twisted pair cable, coaxial cable, optical fiber, infrared, radio link, microwave link and satellite link.

Network devices: Modem, RJ45 connector, Ethernet Card, Hub, Switch, Gateway.

Different Topologies- Bus, Star, Tree; Concepts of LAN, WAN, MAN.

Protocol: TCP/IP, File Transfer Protocol (FTP), PPP, Level-Remote Login (Telnet), Internet, Wireless/Mobile Communication, GSM, CDMA, WLL, 3G, SMS, Voice mail, Application Electronic Mail, Chat, Video Conferencing.

Network Security Concepts: Cyber Law, Firewall, Cookies, Hackers and Crackers.

WebPages; Hyper Text Markup Language (HTML), eXtensible Markup Language (XML); Hyper Text Transfer Protocol (HTTP); Domain Names; URL; Protocol Address; Website, Web browser, Web Servers; Web Hosting.

COMPUTER SYSTEM ORGANISATION

Number System: Binary, Octal, Decimal, Hexadecimal and conversion between two different number systems. Integer, Floating Point, 2�s complement of number from base-2;

Internal Storage encoding of Characters: ASCII, ISCII (Indian scripts Standard Code for Information Interchange), UNICODE;

Microprocessor: Basic concepts, Clock speed (MHz, GHz), 16 bit, 32 bit, 64 bit processors; Types � CISC, RISC; Concept of System Buses, Address bus, Data bus.

Concepts of Accumulator, Instruction Register, and Program Counter;

Commonly used CPUs and CPU related terminologies: Intel Pentium Series, Intel Celeron, Cyrix, AMD Series, Xeon, Intel Mobile, Mac Series; CPU Cache;
Concept of heat sink and CPU fan, Motherboard; Single, Dual and Multiple
processors;

Types of Memory: Cache (L1,L2), Buffer, RAM (DRAM, SDRAM, RDRAM, DDRAM), ROM (PROM, EPROM), Access Time;

Input Output Ports/Connections: Power connector, Monitor Socket, Serial (COM)and Parallel (LPT) port, Universal Serial Bus port, PS-2 port, SCSI port, PCI/MCIsocket, Keyboard socket, Infrared port (IR), audio/speaker socket, Mic socket; data Bus; external storage devices connected using I/O ports;

Power Supply: Switched Mode Power Supply (SMPS): Elementary Concept of
Power Supply: Voltage, Current, Power (Volt, Ampere, Watt), SMPS supplies �
Mother Board, Hard Disk Drive, Floppy Disk Drive, CD/DVD Drive;

Power Conditioning Devices: Voltage Stabilizer, Constant Voltage Transformer (CVT), Uninterrupted Power Supply (UPS)-Online and offline.

Network �Architectures�

A host refers to any device that is connected to your network. Some define ahost as any device that has been assigned a network address.

A host can serve one or more functions:

� A host can request data (often referred to as a client)
� A host can provide data (often referred to as a server)
� A host can both request and provide data (often referred to as a peer)

Because of these varying functions, multiple network �architectures� have been developed, including:

� Peer-to-Peer networks
� Client/Server networks
� Mainframe/Terminal networks

When using a peer-to-peer architecture, all hosts on the network can bothrequest and provide data and services. For example, configuring two Windows XP workstations to share files would be considered a peer-to-peer network.

Though peer-to-peer networks are simple to configure, there are several key disadvantages to this type of architecture. First, data is spread across multiple devices, making it difficult to manage and back-up that data.
Second, security becomes problematic, as you must configure individual permissions and user accounts on each host.

When using a client/server architecture, hosts are assigned specific roles.Clients request data and services stored on Servers. Connecting Windows XP workstations to a Windows 2003 domain controller would be considered a client/server network.

While client/server environments tend to be more complex than peer-to-peer networks, there are several advantages. With data now centrally located on a server or servers, there is only one place to manage, back-up, and secure that data. This simplified management allows client/server networks to scale much larger than peer-to-peer. The key disadvantage of client/server architecture is that it introduces a single point of failure.

When using a mainframe/terminal architecture, often referred to as a thinclient environment, a single device (the mainframe) stores all data and services for the network. This provides the same advantage as a client/server environment � centralized management and security of data.

Additionally, the mainframe performs all processing functions for the dumb terminals (or thin-clients) that connect to the mainframe. The thin clients perform no processing whatsoever, but serve only as input and output devices into the mainframe. Put more simply, the mainframe handles all the �thinking� for the thin-clients.

A typical hardware thin-client consists of a keyboard/mouse, a display, and an interface card into the network. Software thin-clients are also prevalent, and run on top of a client operating system (such as Windows XP or Linux).

Windows XP�s remote desktop is an example of a thin-client application.

- Introduction to Networks -

What is a Network?

A network is defined as devices connected together to share information and services. The types of data/services that can be shared on a network is endless - documents, music, email, websites, databases, printers, faxes, telephony, videoconferencing, etc.

Protocols are �rules� that govern the method by which devices share data and services. Protocols are covered in great detail in subsequent sections.

Basic Network Types

Networks are generally broken down into two types:

LANs (Local Area Networks) - a high-speed network that covers a relatively small geographic area, usually contained within a single building or campus. A LAN is usually under the administrative control of a single entity/organization.

WANs (Wide Area Networks) � The book definition of a WAN is a network that spans large geographical locations, usually to interconnect multiple LANs.

A more practical definition describes a WAN as a network that traverses a public network or commercial carrier, using one of several WAN technologies. Thus, a WAN can be under the administrative control of several entities or organizations, and does not need to �span large geographical distances.�

MAN (Metropolitan Area Network). A MAN is defined as a network that spans several LAN�s across a city-wide geographic area. The term �MAN� is less prevalent than either LAN or WAN.

Number Systems and Binary Arithmetic

Number Systems

This focuses on the way communication takes place inside and among different computer devices.

Types of number systems:

1. Decimal (Denary): In primary school we used to write numbers in terms of Units, Tens, Hundreds and Thousands. Our number system, the DENARY system, bases itself on TEN states 0, 1, 2, 3, 4, 5, 6, 7, 8, 9

2. Binary: A numbering system using the digits "0" and "1" in the decimal system. We know that computers are machines built from microscopic switches with only TWO states: ON or OFF (0 or 1). All computer programs are executed in binary form only. When a user enters data into a computer (such as inputting letters) a translator has to convert that inputted data into its binary equivalent.

3. Hexadecimal: This is a numbering system involving 16 states and is used so that binary data would be easier to be represented.

Weights

A number is made up of digits, where every digit has a certain value of importance. When we were in primary school we were taught to place numbers under Units, Tens, Hundreds and Thousands and so on. What we were being taught was in fact the so-called DENARY WEIGHTS. Let us analyse the real value of a DECIMAL NUMBER.

Suppose we have the decimal number 213910. Each digit has a position. Thus, the digit three has a value of 3 tens(30) and 2 has a value of 2 thousands (2000).

Weights in the Binary System:

Weights can be called Place Values. Similar to the denary weights, there are the binary weights that only differ in the range of digits. Suppose we have the binary number 10101012.

Conversions:

At Matsec Level one needs to remember the following number conversions:

1. From binary to decimal
2. From decimal to binary
3. From binary to hexadecimal
4. From hexadecimal to binary
5. From decimal to hex
6. From hex to decimal

Logic circuits

Electronic circuits which process information encoded as one of a limited set of voltage or current levels. Logic circuits are the basic building blocks used to realize consumer and industrial products that incorporate digital electronics. Such products include digital computers, video games, voice synthesizers, pocket calculators, and robot controls.

All logic circuits may be described in terms of three fundamental elements, shown graphically in the illustration. The NOT element has one input and one output; as the name suggests, the output generated is the opposite of the input in binary. In other words, a 0 input value causes a 1 to appear at the output; a 1 input results in a 0 output. (All signals are interpreted to be one of only two values, denoted as 0 and 1.)

Logic elements.

The AND element has an arbitrary number of inputs and a single output. As the name suggests,the output becomes 1 if, and only if, all of the inputs are 1; otherwise the output is 0. The AND together with the NOT circuit therefore enables searching for a particular combination of binary signals.

The third element is the OR function. As with the AND, an arbitrary number of inputs may exist and one output is generated. The OR output is 1 if one or more inputs are 1.
The operations of AND and OR have some analogies to the arithmetic operations of multiplication and addition, respectively. The collection of mathematical rules and properties of these operations is called boolean algebra.

While the NOT, AND, and OR functions have been designed as individual circuits in many circuit families, by far the most common functions realized as individual circuits are the NAND and NOR circuits of the illustration. A NAND may be described as equivalent to an AND element driving a NOT element. Similarly, a NOR is equivalent to an OR element driving a NOT element.
As the names of the logic elements described suggest, logic circuits respond to combinations of input signals. Logic networks which are interconnected so that the current set of output signals is responsive only to the current set of input signals are appropriately termed combinational logic.

An important further capability for processing information is memory, or the ability to store information. The logic circuits themselves must provide a memory function if information is to be manipulated at the speeds the logic is capable of. Logic circuit networks that include feedback paths to retain information are termed sequential logic networks, since outputs are in part dependent on the prior input signals applied and in particular on the sequence in which the signals were applied.

Several alternatives exist for the digital designer to create a digital system. Two common realizations are ready-made catalog-order devices, which can be combined as building blocks, and custom-designed devices. Gate-array devices comprise a two-dimensional array of logic cells, each equivalent to one or a few logic gates. Programmable logic arrays have the potential for realizing any of a large number of different sets of logic functions. In table look-up, the collection of input signals are grouped arbitrarily as address digits to a memory device. Finally, the last form of logic network embodiment is the microcomputer.

logic circuit, electric circuit whose output depends upon the input in a way that can be expressed as a function in symbolic logic; it has one or more binary inputs (capable of assuming either of two states, e.g., �on� or �off�) and a single binary output. Logic circuits that perform particular functions are called gates. Basic logic circuits include the AND gate, the OR gate, and the NOT gate, which perform the logical functions AND, OR, and NOT. Logic circuits can be built from any binary electric or electronic devices, including switches, relays, electron tubes, solid-state diodes, and transistors; the choice depends upon the application and design requirements. Modern technology has produced integrated logic circuits, modules that perform complex logical functions. A major use of logic circuits is in electronic digital computers. Fluid logic circuits have been developed whose function depends on the flow of a liquid or gas rather than on an electric current.

Number systems and computer codes

Computer works with binary number system that is consist of only two digits zero and one. Inside the computer binary number is represented by an electrical pulse. One means a pulse of electricity and zero means no pulse. All the data enters into the computers first converts into the binary number system. One digit in binary number system is called bit and combination of eight bits is called byte. A byte is the basic unit that is used to represent the alphabetic, numeric and alphanumeric data.

Data is the combination of characters, numbers and symbols collected fro a specific purpose.
Data is divided into three types; alphabetic data, numeric data and alphanumeric data.
Numeric data consist of ten digits 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, two signs + and � and decimal point . There are different types of number system that are used to represent numeric data.
These number systems are decimal number system, binary number system, octal number system and hexadecimal number system.

Alphabetic data is used to represent 26 alphabetic. It consist of capital letters from A to Z, small letters from a to z and blank space. Alphabetic data is also called non numeric data.

Alphanumeric data used to represent alphabetic data, numeric data, special character and symbols.

Any type of data is represented in computer as binaries. The binaries are the 1 or 0. Actually the 1 mean ON and 0 mean OFF. This combination can represent any type of data.

For example, we want input the letter A.This letter will be converted to its binary codes by using ASCII (or any other which is used by computer) codes.The code for A letter is 65.The 65will be converted to its binary equivalent which is 01000001.By using same logic any type of data is represented in computer.

Following are the types of data.

Numerical data: the numerical data consists of numbers only (decimal or float) e.g. 28774,
383.38, 3238.

Alphabetical data: The alphabetical data consists of letters and symbols e.g. car, bridge, man.

Alphanumerical data: This type of data is the combination of alphabetical data and numerical
data e.g. Abc23, 34 New street.

Apart from these types of data the data can be in the form Audio visual data, physical data, Musical data. These types of data is provided by using special kind of hardware. The use of these data types is not limited and the examples of such data can be seen easily.

Computer is a system to manipulate data. Monitor, where we see data, is not the place to store them (though one of the police team had ceased the monitor to investigate a case of data theft!). It is the secondary storage devices (hard disk, floppy disk, CD, DVD, etc.) where the data are stored. Whatever we write through the keyboard or try to push through the various input devices, the corresponding input devices convert them first into digital signals to produce 0 or 1 (bits). These continuous streams of bits are then stored or represented signifying the non-availability or availability of the voltage. To avoid further ambiguity in retrieval, these bits are stored and accessed in a group, say 8 bits together. The group of 8 bits is called byte and thus the higher units of bit calculation are the KB (1 KB = 1024 bytes), MB (1 MB = 1024 KB), GB (1 GB = 1024 MB), etc.

There exist several kinds of data such as Textual, Numerical, Alphanumerical, logical, Pictorial or Audiovisual. Each type of data has some pre-defined way of representation and other behaviour inside the computer. The textual data are the alphabetic character set of any language whereas the digits constitute the numeric part of the data. The mixture of alphabetic and numeric data together form the alphanumeric character sets. The logical data are those that help to analyse the comparison concept. Pictures and sounds create the pictorial and audiovisual data for the computer.

Data Types

A data type is a type of data. Of course, that is rather circular definition, and also not very helpful. Therefore, a better definition of a data type is a data storage format that can contain a specific type or range of values.

When computer programs store data in variables, each variable must be assigned a specific data type. Some common data types include integers, floating point numbers, characters,strings, and arrays. They may also be more specific types, such as dates, timestamps, boolean values, and varchar (variable character) formats.

Some programming languages require the programmer to define the data type of a variabl before assigning it a value. Other languages can automatically assign a variable's data type when the initial data is entered into the variable. For example, if the variable "var1" is created with the value "1.25," the variable would be created as a floating point data type. If the variable is set to "Hello world!," the variable would be assigned a string data type. Most programming languages allow each variable to store a single data type. Therefore, if the variable's data type has already been set to an integer, assigning string data to the variable may cause the data to be converted to an integer format.

Data types are also used by database applications. The fields within a database often require a specific type of data to be input. For example, a company's record for an employee may use a string data type for the employee's first and last name. The employee's date of hire would be stored in a date format, while his or her salary may be stored as an integer. By keeping the data types uniform across multiple records, database applications can easily search, sort, and compare fields in different records.

Computer software

What is Software?

Software is a set of instruction written to interface between user and machine.

Who writes this instructions?

Programmers writes this instructions.

How the programmers write the instructions /software?

They use computer languages to write software applications.

Software can be divided into three main categories:

- Languages
- Applications
- Operating Systems (OS)

LANGUAGE:

It is one of the software type, use to write extensive applications and operating systems It did not contains any limitations in programming. By using the languages you can write any thing for a computer.

For instance just imagine a language like a piece of cloth with that you want to make a shirt or paint curtain for windows or door, than you will take that cloth to the tailor and have him made for you or if you know tailoring you can stitch it at home.

Where as: Cloth is Computer Language
Tailor is Computer programmer
Shirt/Paint is Computer application

Example of languages are:

- CC++
- Fortran
- Cobol
- Pascal
- Perl
- Assembly Language
- Machine Language
- Java
- VB.NET
- C#
- Oracle Forums

APPLICATION:

Software applications are user friendly and most of the time it is custom made for the end-user. Because it serving a specific purpose so it is having its own limits and bounds. It will not work beyond its bounding, for example if you want design picture in a word editor you may not able to get the result according to your desire.

Following are the different categories of applications

- Database Applications
- Front End Applications
- Reports Applications
- Word Editors
- Spread Sheets Editors
- Application for presentation
- Graphics Designing Application
- CAD designing Application
- Computer Games
- SCADA Applications

Some of the popular Applications are:

- Oracle
- MSoffice (Word,Excel,Access,PowerPoint,Outlook, etc.)
- VB
- VC++
- Autocad

OPERATING SYSTEM:

This is the interface between user and computer or man and machine. This is the main and mandatory software in computer. Without Operating System (OS) computer will never starts. It is the mediator between you as an user and computer.

Think that you are suppose to talk to a person who does not understand your language. What you will do in this situation? Off course you take the help of person who knows both yours and other person's language, he is the mediator. And that's what the computer Operating System is doing.

It is very interesting that the thing from which OS has comes out still require OS to run on. In other words all languages and applications require a platform which is nothing but OS. So that conclusion on any computer first should have OS than you can have language or application on it.

Example of some of the Operating Systems:

- Windows
- Unix
- Linux
- Apple Mach
- Solaris
- Ban
- VMS
- RS
- OS2
- IRIX
- AIX
- HP-UX

Types of Computers

Definition of a Computer

A computer can be defined as an electronic device that receives input from the user through a mouse or keyboard, processes it in some fashion and displays the result on a screen. It can also be assumed as any device that has a microprocessor in it.

Types of Computers

Fundamentally, there are two types of computers

• analog
• digital
  

Analog computers solve problems by using continuously changing data such as

• temperature
• pressure
• voltage

Digital computers solves problems by manipulating discrete binary digits (1s and 0s).

3 Main Types of Computers

• mainframes
• minicomputers
• microcomputers
  

They differ in size, speed of operation, amount of data that can be stored, and the number of simultaneous users.

Microcomputers:

• Personal or desktop computer designed for general use by a single person.
• Home and all types of businesses.
• Entertainment, communication, personal databases, and spreadsheets, word processing, accounting, inventory control, research.
  

Minicomputers:

• Mid-range servers supporting smaller number of simultaneous users, typically 50 to 100.
• Larger businesses.
• Accounting, billing, and inventory records.
  

Mainframe computers:

• Allow many simultaneous users.
• Industry, research, and university computing centers.
• Typically huge databases, complex mathematical operations, processing millions of transactions everyday.
  

Types of Computers Based on Size

Desktop - A Personal Computer that is not designed for portability. The computer is set up in a permanent location. Most desktops offer more power, storage and versatility for less cost.

Laptop - These are also called notebooks. Laptops are portable computers that integrate the display, keyboard, a pointing device or trackball, processor, memory and hard drive all in a battery-operated package slightly larger than an average hardcover book.

Palmtop - More commonly known as Personal Digital Assistants (PDAs)

• Palmtops are tightly integrated computers that often use flash memory instead of a hard drive for storage
• These computers usually do not have keyboards but rely on touchscreen technology for user input
• Palmtops are typically smaller than a paperback novel, very lightweight with a reasonable battery life. A slightly larger and heavier version of the palmtop is the handheld computer.
  

Workstation - A desktop computer that has a more powerful processor, additional memory and enhanced capabilities for performing a special group of task, such as 3D Graphics or game development.

Server - A computer that has been optimized to provide services to other computers over a network. Servers usually have powerful processors, lots of memory and large hard drives.

Supercomputer- This type of computer usually costs hundreds of thousands or even millions of dollars. Although some supercomputers are single computer systems, most are comprised of multiple high performance computers working in parallel as a single system. The best known supercomputers are built by Cray Supercomputers.

Wearable- The latest trend in computing is wearable computers. Common computer applications (e-mail, database, multimedia, calendar/scheduler) are integrated into watches, cell phones, even clothing!

Basic Units of a Computer

Modular units usually consist of the following separate components:

• The Computer
• The Monitor
• The Keyboard
• The Mouse
• Peripherals
• Central Processing Unit (CPU)
  

Central processing unit (CPU):

The heart of the computer, this is the component that actually executes instructions organized in programs ("software") which tell the computer what to do.

Storage Devices

Memory(fast, expensive, short-term memory): Enables a computer to store, at least temporarily, data, programs, and intermediate results.

Mass storage device (slower, cheaper, long-term memory): Allows a computer to permanently retain large amounts of data and programs between jobs. Common mass storage devices include disk drives and tape drives.

Input Devices

1. Keyboard
2. Mouse
3. Tracker ball
4. Joystick
5. Light pen
6. Digial Camera
7. Microphone
8. Touch screen
9. Video Digitiser
10. Graphics tablet
11. Scanner
12. OCR (Optical Character Recognition)
    

Output Devices

1. Monitors or Visual Display Units (VDUs)
2. Printers
3. Plotters
4. Speakers LCD
5. projectors
   

Written By Santhosh