A second, safe copy of a file, letter or data. You should do regular backups of your important work in case something goes wrong and you erase it. It might seem boring at the time,. But its far more boring to type all the information back in again. Normally you back up data on a little cassette tape or, if you don't have too much, on to floppy disks. Windows has a utility that makes backing up easy. You tell in which folder, directory or file you want to copy and whether you want to make a backup to a floppy disk or tape. Once you have made a backup, keep it well away from your main computer.

Bad sector

A fault in a floppy disk or hard disk. Disks are divided into tracks which contain many sectors. If you have a bad sector, it means the disk surface has been damaged at this point and that the disk drive cannot read the data there. To fix it, use the disk tools you will find in Windows 95 or run Scandisk from the DOS prompt. For serious faults, use a special program like Norton's Disk Doctor.


This refers to the difference (measured in Hz), between the highest and lowest frequencies of a transmission. Most people loosely refer to bandwidth as the amount of data that can be transferred over a network connection.

BAT or batch file

The three-letter file name extension given to batch program files that contain batch commands stored as text. A batch file contains DOS commands that you can type at the DOS prompt, together with other control commands. It's a convenient way of grouping a series of commands you need to run frequently. To run all the commands stored in batch file, just type in the name of the file without its .BAT extension and each line will be run consecutively. When you first switch on your PC a batch file called AUTOEXEC.BAT is run. This contains all the setup and configuration commands that define the environment and set up any special devices like a CD-ROM drive. To see if you have any batch files on your hard disk, use the DIR*.BAT command from the DOS prompt or the File Manager in Windows and look for .BAT file extension. To see what's inside a batch file, use the Type command in DOS .

Baud rate

The speed at which data is transmitted over telephone lines. For example, a 2400-baud modem sends data at a rate of 2,400 bits (about 300 characters) per second. Two modems can only connect if they can operate at the same baud rate.


Bulletin Board System (see bulletin board).

Beta software

An early version of a software product that is being tested and is not yet working properly. Avoid using beta software regularly, since it is not 100 percent reliable. When all the problems have been found and fixed, the software is then released. Often PC magazines will test beta versions of a new software program to give readers an idea of what the finished version will be like when it comes out .

Bezier curve

A geometric curve where shape is defined by two endpoints, called control handles. It's like an elastic band that you can pin down at each end and then more the middle bit around to the shape you want .


The common name for base two maths. In binary, the smallest unit is a bit (short for a binary digit). This can have one of just two values: 0 or 1. Computers count using base two, since the two values are easy to represent electrically: as 0 volts for zero and (normally) 5 volts for a one .


Stands for Basic Input/Output System, and is pronounced bye-oss. This is a series of instructions that manages the basic functions in your PC. For example, the BIOS looks after how the keyboard works and makes sure the right character code is sent when you press a key. It also manages the disk drives and the monitor. You don't have to worry about the BIOS, and you are very unlikely to ever see it, since it's stored on a special chip inside your computer .


A binary digit, the smallest unit of data used in a computer; 7 or 8 bits are typically used to represent a single character of text.

Bits Per Second (bps)

The speed at which bits are transmitted.


Images and fonts are made up of tiny dots or pixels. If you zoom in close to a bitmap image you will see the dots grow. Compare this with a vector image, in which the shapes are described mathematically, so they appear sharp however much you zoom in .


The three letter file-name extension that's given to files that store bitmap image data. If you use the Paint utility in Windows, you can save or open BMP files created in any other paint program.


A computer network devoted to academic use that provides email and file transfer services using a store-and-forward protocol. It is based on the IBM Network Job Entry protocols. A more recent version of Bitnet (known as Bitnet-II) encapsulates the Bitnet protocol within IP packets.

Boot, boot up

To start up a computer. This is process carried out when your PC is switched on. First, a sequence of instructions stored with the BIOS in a chip are executed and they tell the computer to look on the boot disk for the main operating system. The PC tests the floppy drive A: and then the hard drive C: for a valid boot disk that contains the operating system

Boot disk

Disk containing the operating system that is loaded when a PC is switched on. The boot up instructions tell the hardware to read in the operating system software. Normally, the boot disk is your main hard disk. But you can use a floppy disk as a boot disk , if it is formatted as a system or boot disk.


If you send email and it fails to arrive at its intended recipient for any reason (incorrect user name, network failure, etc.), the message "bounces" and returns to you. The subject line in a bounced message usually says something like: Undeliverable Mail or Message Undeliverable.


A signal sent from a user's terminal to the network, which causes interruption of an activity.


To move through a multimedia program or through a list of files in no particular order. You control which page you go to next and what you view .


An error in a program that means it does not work properly. (See also Beta).


A symbol- often a filled circle or square- printed in front of a line of text to draw attention to it. If you are using a Windows word processor, you can add bullet by changing the font to Symbol or Windings .

Bulletin Board Service (BBS)

Computer you can call up and connect to via a modem and a phone line. Bulletin boards normally have a lots of free software that you can download, together with areas called forums where you can discuss topics with other users. More sophisticated systems have links to other bulletin computers or even the internet. When you sign up with a BBS you are given an account which has your own user name and password. To use it again, you need to enter your user name and password. To access a bulletin board you need to have a modem. You also need communications software. All versions of Windows come with free communications software to get you started. In Windows 3.x this is called Terminal; in Windows 95 it's called Hyper Terminal. Some professional on-line services, like CompuServe, have their own communications software .


A group of eight bits -that's eight binary digits-which is the usual form in which data is manipulated within a computer. One byte can hold numbers between 0 and 255. For example, each different letter of the alphabet, numeral and punctuation mark has a special code that describes it (see ASCII) code. This code is stored within one byte, and so your computer can identify 256 different characters .