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Definitions of computer

Definition- A computer is a device that accepts information (in the form of digitalized data) and manipulates it for some result based on a program or sequence of instructions on how the data is to be processed

A computer is a machine that manipulates data according to a set of instructions. Although mechanical examples of computers have existed through much of recorded human history, the first electronic computers were developed in the mid-20th century (1940–1945). These were the size of a large room, consuming as much power as several hundred modern personal computers (PCs).[1] Modern computers based on integrated circuits are millions to billions of times more capable than the early machines, and occupy a fraction of the space.[2] Simple computers are small enough to fit into a wristwatch, and can be powered by a watch battery. Personal computers in their various forms are icons of the Information Age and are what most people think of as "computers". The embedded computers found in many devices from MP3 players to fighter aircraft and from toys to industrial robots are however the most numerous. The ability to store and execute lists of instructions called programs makes computers extremely versatile, distinguishing them from calculators. The Church– Turing thesis is a mathematical statement of this versatility: any computer with a certain minimum capability is, in principle, capable of performing the same tasks that any other computer can perform. Therefore computers ranging from a mobile phone to a supercomputer are all able to perform the same computational tasks, given enough time and storage capacity. A computer is a physical collection of bits that you can touch. The screen, main system box, keyboard and mouse etc. But inside is this mystical stuff called software. Before we look at it, let's have a look inside the computer. At its simplest a computer is made up of the following parts, most of them in the system unit. • •

A Central Processing Unit (also called a CPU) Read-Only Memory (ROM) that holds Permanently Stored instructions.

Random Access Memory (RAM) to hold software and data. Input and Output Devices such as Screen, Keyboard, Mouse and Printer. A permanent storage device such as a hard disk, floppy disk or Flash drive,Pen drive,Memory card etc. • • •

But what exactly is software? It is the combination of Instructions and Data, known as machine code that forms the building blocks of applications such as Word Processor, Computer Game or Spreadsheet. This machine code lives in the memory of the computer as billions of little on off switches. Exactly the same as a number in a calculator. The CPU is the Brain The heart of the computer is the CPU plus its RAM. The CPU fetches data from RAM, carries out operations on the data and then stores it back in RAM. The CPU can also fetch data from permanent storage such as ROM, floppy disk, Flash or hard disk. It's permanent because when the power is switched off, a copy remains there. The data in memory (RAM or ROM) is organised in blocks of 8 switches. Each switch is known as bit and a block is a byte. Each bit can be On or Off. When a bit is On, it has the value 1, when its Off it has the value 0. This is called Binary Notation. There are 256 different combinations of 8 bits with the values 0 to 255. Table of Bit Values • • • • • •

Bits - Value 00000000 00000001 00000010 .. 11111111 -

0 1 2 255

Binary Conversion 101

In normal numbers, a value like 456 is made up of 4 x 100 + 5 x 10 + 6 x 1. This is a base 10 number. 10112 is a base 2 number which is equal to 8 x 1 + 4 x 0 + 2 x 1 + 1 x 1 = 11 in base 10. Most programmers don't need or use binary, but in C it can be a useful skill to have. A CPU handles data in multiples of 8 bits. In the 1980s when Home Computers like the CBM-64 existed, the CPUs were 8 bit processors, reading single bytes of data and could only execute three hundred thousand instructions per second. Now they can handle 64 bits of data in one go. Longer bit length means that the CPU is faster as it processes more data with each instruction. How Big is a Program? Computer programs can be as small as a few hundred bytes or as large as a few billion bytes. When a program is loaded into RAM from disk, the pattern of the bits is copied exactly- even one bit wrong can cause the program to fail. Computer hardware has been engineered so this doesn't happen. If an application is 40 Megabytes in size, then roughly 320 Million bits are copied into RAM. The prefix Kilo, Mega and Giga indicate the size of a program or data file in bytes. A Kilobyte is 1024 bytes, a Megabyte is 1024 Kilobytes and a Gigabyte is 1024 Megabytes. Put another way, a Gigabyte is 8,589,934,592 individual on/off switches! Instructions are just data The CPU is driven by machine code instructions and data - this is the stuff of software, just a pattern of bits in RAM. Instructions and data are indistingushablethey're just bit patterns. A typical CPU can read and process hundreds of millions of instructions each second. It is possible to program computers by just entering numbers directly into RAM but it is a very tedious and unproductive way of doing things.

What is Software and Types of software

A layer structure showing where Operating System is located on generally used software systems on desktops Practical computer systems divide software systems into three major classes[citation needed] : system software, programming software and application software, although the distinction is arbitrary, and often blurred.

System software System software helps run the computer hardware and computer system. It includes combination of the following: • • • • •

device drivers operating systems servers utilities windowing systems

The purpose of systems software is to unburden the applications programmer from the details of the particular computer complex being used, including such accessory devices as communications, printers, readers, displays and keyboards, and also to partition the computer's resources such as memory and processor time in a safe and stable manner.

Programming software Programming software usually provides tools to assist a programmer in writing computer programs, and software using different programming languages in a more convenient way. The tools include:

• • • • •

compilers debuggers interpreters linkers text editors

An Integrated development environment (IDE) is a single application that attempts to manage all these functions.

Application software Application software allows end users to accomplish one or more specific (not directly computer development related) tasks. Typical applications include: • • • • • • • • • • • • • • •

industrial automation business software computer games quantum chemistry and solid state physics software telecommunications (i.e., the internet and everything that flows on it) databases educational software medical software military software molecular modeling software image editing spreadsheet Word processing Decision making software Application software exists for and has impacted a wide variety of topics.

What is Hardware? Your PC (Personal Computer) is a system, consisting of many components. Some of those components, like Windows XP, and all your other programs, are software. The stuff you can actually see and touch, and would likely break if you threw it out a fifth-story window, is hardware. Not everybody has exactly the same hardware. But those of you who have a desktop system, like the example shown in Figure 1, probably have most of the components shown in that same figure. Those of you with notebook computers probably have most of the same components. Only in your case the components are all integrated into a single book-sized portable unit.

Figure 1 The system unit is the actual computer; everything else is called a peripheral device. Your computer's system unit probably has at least one floppy disk drive, and one CD or DVD drive, into which you can insert floppy disks and CDs. There's another disk drive, called the hard disk inside the system unit, as shown in Figure 2. You can't remove that disk, or even see it. But it's there. And everything that's currently "in your computer" is actually stored on that hard disk. (We know this because there is no place else inside the computer where you can store information!).

Figure 2 The floppy drive and CD drive are often referred to as drives with removable media or removable drives for short, because you can remove whatever disk is currently in the drive, and replace it with another. Your computer's hard disk can store as much information as tens of thousands of floppy disks, so don't worry about running out of space on your hard disk any time soon. As a rule, you want to store everything you create or download on your hard disk. Use the floppy disks and CDs to send copies of files through the mail, or to make backup copies of important items. Random Access Memory (RAM) There's too much "stuff" on your computer's hard disk to use it all at the same time. During the average session sitting at the computer, you'll probably use only a small amount of all that's available. The stuff you're working with at any given moment is stored in random access memory (often abbreviated RAM, and often called simply "memory"). The advantage using RAM to store whatever you're

working on at the moment is that RAM is very fast. Much faster than any disk. For you, "fast" translates to less time waiting and more time being productive. So if RAM is so fast, why not put everything in it? Why have a hard disk at all? The answer to that lies in the fact that RAM is volatile. As soon as the computer is shut off, whether intentionally or by an accidental power outage, every thing in RAM disappears, just as quickly as a light bulb goes out when the plug is pulled. So you don't want to rely on RAM to hold everything. A disk, on the other hand, holds its information whether the power is on or off. The Hard Disk All of the information that's "in your computer", so to speak, is stored on your computer's hard disk. You never see that actual hard disk because it's sealed inside a special housing and needs to stay that way. Unlike RAM, which is volatile, the hard disk can hold information forever -- with or without electricity. Most modern hard disks have tens of billions of bytes of storage space on them. Which, in English, means that you can create, save, and download files for months or years without using up all the storage space it provides. In the unlikely event that you do manage to fill up your hard disk, Windows will start showing a little message on the screen that reads "You are running low on disk space" well in advance of any problems. In fact, if that message appears, it won't until you're down to about 800 MB of free space. And 800 MB of empty space is equal to about 600 blank floppy disks. That's still plenty of room! The Mouse Obviously you know how to use your mouse, since you must have used it to get here. But let's take a look at the facts and buzzwords anyway. Your mouse probably has at least two buttons on it. The button on the left is called the primary mouse button, the button on the right is called the secondary mouse button or just the right mouse button. I'll just refer to them as the left and right

mouse buttons. Many mice have a small wheel between the two mouse buttons,

as illustrated in Figure 3. Figure 3 The idea is to rest your hand comfortably on the mouse, with your index finger touching (but not pressing on) the left mouse button. Then, as you move the mouse, the mouse pointer (the little arrow on the screen) moves in the same direction. When moving the mouse, try to keep the buttons aimed toward the monitor -- don't "twist" the mouse as that just makes it all the harder to control the position of the mouse pointer. If you find yourself reaching too far to get the mouse pointer where you want it to be on the screen, just pick up the mouse, move it to where it's comfortable to hold it, and place it back down on the mousepad or desk. The buzzwords that describe how you use the mouse are as follows: • •

Point: To point to an item means to move the mouse pointer so that it's touching the item. Click: Point to the item, then tap (press and release) the left mouse button.

• • • •

Double-click: Point to the item, and tap the left mouse button twice in rapid succession - click-click as fast as you can. Right-click: Point to the item, then tap the mouse button on the right. Drag: Point to an item, then hold down the left mouse button as you move the mouse. To drop the item, release the left mouse button. Right-drag: Point to an item, then hold down the right mouse button as you move the mouse. To drop the item, release the right mouse button.

The Keyboard Like the mouse, the keyboard is a means of interacting with your computer. You really only need to use the keyboard when you're typing text. Most of the keys on the keyboard are laid out like the keys on a typewriter. But there are some special keys like Esc (Escape), Ctrl (Control), and Alt (Alternate). There are also some keys across the top of the keyboard labeled F1, F2, F3, and so forth. Those are called the function keys, and the exact role they play depends on which program you happen to be using at the moment. Most keyboards also have a numeric keypad with the keys laid out like the keys on a typical adding machine. If you're accustomed to using an adding machine, you might want to use the numeric keypad, rather than the numbers across the top of the keyboard, to type numbers. It doesn't really matter which keys you use. The numeric keypad is just there as a convenience to people who are accustomed to adding machines.

Figure 4 Most keyboards also contain a set of navigation keys. You can use the navigation keys to move around around through text on the screen. The navigation keys won't move the mouse pointer. Only the mouse moves the mouse pointer.

On smaller keyboards where space is limited, such as on a notebook computer, the navigation keys and numeric keypad might be one in the same. There will be a Num Lock key on the keypad. When the Num Lock key is "on", the numeric keypad keys type numbers. When the Num Lock key is "off", the navigation keys come into play. The Num Lock key acts as a toggle. Which is to say, when you tap it, it switches to the opposite state. For example, if Num Lock is on, tapping that key turns it off. If Num Lock is off, tapping that key turns Num Lock on. Combination Keystrokes (Shortcut keys) Those mysterious Ctrl and Alt keys are often used in combination with other keys to perform some task. We often refer to these combination keystrokes as shortcut keys, because they provide an alternative to using the mouse to select menu options in programs. Shortcut keys are always expressed as: key1+key2 where the idea is to hold down key1, tap key2, then release key1. For example, to press Ctrl+Esc hold down the Ctrl key (usually with your pinkie), tap the Esc key, then release the Ctrl key. To press Alt+F you hold down the Alt key, tap the letter F, then release the Alt key.