Originally someone who was fascinated by computers and tried to program them as efficiently as possible or explore how they worked. Now normally used to refer to someone who is trying to break into a secure computer system for criminal purposes, such as someone trying to discover a way into a bank.

Half Duplex

Communication that alternates between sending and receiving.

Hand-held scanner

A small device that plugs into a controller card in your PC. The scanner contains a row of light-sensitive cells along its bottom surface. When you drag the scanner over an image, it reads the amount of light reflected from the image or photograph and converts this into a form which can be displayed on your PC. When you buy a hand-held scanner it normally comes with the special controller card that plugs inside your PC.


In a graphics or DTP program, a small square that's displayed on the edge of the frame, object or image. If you move the mouse pointer over the handle and click and drag with the mouse, you will resize or move it.


A procedure performed by modems, terminals, and computers to verify that communication has been correctly established.


A slang term that means your computer has stopped responding because of a temporary fault. Some programs which are not tested thoroughly are liable to stop at unpredictable times and hang the computer. This means that you cannot do anything else except switch off your PC and start again.

Hard Copy

A printed document or copy of an image that's stored on computer.

Hard disk

A rigid magnetic disk that is able to store many times more data than a floppy disk. Usually it cannot be removed from the disk drive that's located inside your PC. In most PCs the hard disk drive is called drive C:, whereas the floppy disk drive is called drive A: or B:. A hard disk drive can normally store several hundred million bytes (or characters) of information, whereas a floppy disk can only store one and a half million bytes. If you hear a clicking or whirring sound when you save a document, that's the hard disk working .


Any physical unit, hard disk, monitor or electronic circuit that is part of a computer system.

Hayes modem

Most modems in use today are "Hayes-compatible" modems, with a standard set of alphanumeric commands.


A function in an application that displays text on screen to explain how to use the software or how use a particular function. Context-sensitive help displays explanatory text about the particular control or command you are using rather than about the general program. Most software applications running under Windows on a PC link the help text to the F1 key.

Help key

A particular key on the keyboard that is linked to the help system of a software program. Most Windows applications on a PC have standardised on the F1 key as the help key. Just press this key at any time and the software will display explanatory text that should help you understand the function or command you are puzzling over.

Hidden files

Your PC has a whole range of important and private files that you have probably never seen. If you list the files through the Explorer or by using the DIR command at the DOS prompt, the operating system software will not show you the hidden files. These are files that have had a special flag set so that they are not displayed and cannot be easily deleted. If you really want to see all the files on your hard disk, use the Attrib command .


To select a word or section of text in a document by moving the mouse pointer over the word and double-clicking on the mouse button. In Word for Windows, a double-click will highlight the word you are over, a triple-click highlight the line, and a quadruple-click will highlight the paragraph.

Home key

A key on the PCs keyboard in the group above the four cursor keys. It will move the cursor to the start of the current line. Some word processing programs will move the cursor to the start of the document if you press the Home key twice.

Horizontal scroll bar

A bar at the bottom of a window which indicates there is more information that can be displayed in the window. You can display the rest of the information by clicking on the arrow buttons at each end of the scroll bar.


A computer that is attached to a network or the Internet. Hosts allow users on client machines to connect and share files or transfer information. Individual users communicate with hosts by using client application programs.


The name given a host computer connected to the Internet.

Host Address

The address of a host computer on the Internet.

Hot key

A way of selecting a menu option or command by pressing two or more keys at the same time. For example, instead of selecting the File/Save menu option, most Windows programs use a hot key shortcut of ALT-S (the Alt key and the S key pressed at the same time) to do the same thing. Another useful hot key shortcut is Alt-F4 which will quit any Windows program.


In a multimedia title, an area of an image that does something if you move the mouse pointer on to it and click on the mouse button. Normally, you can tell that there is a hotspot in an image because the mouse pointer changes shape from an arrow to a hand. For example, if the multimedia title displayed a picture of a guitar, there could be a hotspot over each string which would play the sound of the string being plucked.


Stands for Hyper Text Markup Language. A series of special code that define the typeface and style that should be used when displaying the text and also allow hypertext links to other parts of the document or to other documents. HTML is used to create documents for the graphical part of the internet, the World Wide Web. A document coded in HTML can be displayed on any viewer software that understands HTML, Such as Mosaic or Netscape Navigator.


The combination of hypertext and multimedia in an online document.


A communications program that is included with Windows 95 and allows you call a remote computer via a modem and transfer files. It's not meant to be used to access the Internet. It's more useful when used to access bulletin boards or other online services.


A type of text that allows embedded links to other documents. Clicking on or selecting a hypertext link displays another document or section of a document. Most World Wide Web documents contain hypertext.