"The Atari A to Z" by Mark S Baines Copyright (c) 1998 Mark S Baines All Rights Reserved YOU MUST READ "READ_ME.NOW" BEFORE YOU LOOK AT ANY OF THIS FILE ***************************************************************************** H HAL Hard Array Logic. A read-only version of a user-programmable PAL device which contains hundreds or thousands of logic gates which have been manufactured with the connections between them 'hard-wired' to a customer's specification. HALs are used when a successful PAL needs to be produced in quantity. Half-duplex In a communications system, when messages are sent in both directions but only one direction at a time. Halt To stop the execution of a sequence of instructions, usually temporarily. Handle A fictitious name or monicker of a person usually on a communications system. Also, the identifying name given to a GEM object in programming source code, such as a windows object. Also, a small square attached to the corners and centre of the four edges of a frame in a WIMP environment program. By grabbing a handle (hold down a mouse button and move) the frame can be re-sized to the desired position. See Frames. Handshaking The initial interchanges made between modems on a communications system, before transmitting data, to establish a common protocol. Hard copy A copy on paper, a printout. Hard disk - HD, HDD An aluminium magnetizable storage disk. Hard disk units used in micros are of the Winchester type and usually consist of more than one aluminium disk (a platter) mounted above another on a rotating spindle forming a stack. Because these stacks are rigid they can be rotated at 3,600 rpm and have the head extremely close to the surface (less than a particle of smoke or dust, which is why they exist in hermetically sealed cases) enabling a smaller track width and therefore a greater capacity than floppy disks of the same size. Common disk diameters are 5.25 inch and 3.5 inch whereas 2.5 inch and 2 inch disks are becoming common in notebook style portable computers. The Falcon can be fitted internally with a 2.5 inch hard disk unit. See Disk and Floppy. Hardware Any electrical, mechanical or structural part of a computer system. Hardware scrolling The hardware scrolling introduced with the STE is the provision of some extra registers and a facility to allow the screen's memory address to be set to point to word boundary increments instead of the ST's 256-byte boundaries. It is possible to implement horizontal and vertical scrolling by pre-preparing the screen bitmap and moving the screen address pointer. By moving the pointer 160 bytes (the number of bytes in a normal screen line) vertical scrolling will result. Of the three new registers, HSCROLL contains the horizontal pixel scroll offset thus allowing for smooth single-pixel scrolling. LINEWID indicates the number of extra words of data which represent a single display line thus allowing for virtual screens wider than that displayed. Line-wise and pixel-wise scrolling are achievable as is vertical split screens. Hard wired Bypassing a communications link or electrical components by means of a direct cable. Hash The ASCII character 35 '#', a symbol meaning 'number' in the US. Also, to perform arithmetic operations with numbers that have no numerical significance. Hash total A control total formed by adding the contents of a field, such as the account number or customer name, in each record of a group. These fields don't contain numbers except that the characters are represented as binary numbers in storage and it is these that are added. Hashing algorithm An algorithm used in constructing and maintaining hashed random files by which record keys are modified to produce their addresses in an address space of the file in storage. HBL Horizontal BLank interrupt. A MC680x0 processor interrupt that is generated every time the video raster scan line returns from the right-hand side of the screen to the left-hand edge of the next scan line. On the ST this interrupt occurs every 50 to 64 ęs depending on the resolution (mono or colour). Although occurring very often, this interval does not allow for very many instructions to be carried out in that time and so is not important except for certain screen effects, such as displaying more colours on the screen than the normal system allows. The VBL interrupt is much more useful. HC High-speed Cmos. CMOS logic semiconductor devices were not particularly fast until HC technology speeded them up. Such chips have the letters 'HC' in their names, such as a MC68HC000 and have mostly replaced ordinary CMOS chips. HCT High-speed Cmos Ttl. A HC CMOS chip with TTL inputs. These provide a means of connecting HC-type chips to TTL logic. HCR Handwritten Character Recognition. Computer input equipment and techniques for identifying handwritten characters using a stylus and the pen-stroke information directly. Such a system is used on the Atari Stylus computer. HD High Density. HD Hard Disk. HDD Hard Disk Drive. HD6301 The ST-Falcon range keyboard processor responsible for polling the keyboard for input as well as from the mouse and joysticks. The 6301 runs at 1 MHz and is effectively, an 8-bit microprocessor with 4 K ROM and 128 bytes of RAM, input/output lines and a serial interface which handles the traffic to and from the main motherboard, especially the ACIA. The ROM contains Atari's custom keyboard driver program. The HD6301 is designed to operate independently of the central processor, relieving it from these time consuming tasks. It also contains a real-time clock which counts in one second increments. HDX Atari's hard disk driver and utility software, generally not regarded to be as good as third party drivers from ICD and Supra. Head One or more electromagnets or transducers used to read and write data in bit- pattern form onto the magnetizable surface of a disk or tape. On floppy disks and tape systems these heads touch the recording surface. In Winchester hard disks, they fly above the surface on the air boundary layer, only touching the surface when they come to rest. Head crash When a head meets the surface of a hard disk in an uncontrolled manner resulting in irreparable damage of that surface and loss of data. Header block Data placed at the beginning of a block of data to identify or define it for storage or transmission, e.g. at the start of a metafile. There is typically a header at the beginning of each sector on a disk used to confirm the positioning of the read/write heads. Also, the block of data at the beginning of GEMDOS executable files containing important information required by that program. See Program header. Header file A file with a .H file name extender containing definitions of functions, types and macros needed for the compilation of C/C++ programs. Heat sink Part of a semiconductor designed to dissipate heat generated during operation. Help key Atari keyboard key whose action is usually defined by a program, except that TOS assigns the combination [Alt-Help] to cause a screen dump to the printer. Help menu A GEM program menu containing guidance on the program's use. Hercules A IBM PC compatible screen display system that provides 720 x 348 pixel monochrome graphics display and an 80 x 25 text mode. Hertz - Hz The unit of frequency equal to one cycle per second. Hex, HEX HEXadecimal. Hexadecimal - Hex A number system with a radix of sixteen, frequently used to represent binary numbers. The digits are 0-9 followed by A-F, F being equal to decimal fifteen. To distinguish them from decimal numbers (or other character sequences) hex numbers are usually preceded with a '$' character, as in $00FC0000. HGC Hercules Graphics Card. See Hercules. Hidden line In a two-dimensional display of a three-dimensional object, a line that could not be seen when viewing the 'real' object and so should not appear in the display. Hide To make an object, such as the mouse, invisible. Hierarchy An organization of items on different levels in which the upper items have a precedence or control over the lower levels. The TOS filing system is hierarchical with its root directory and subdirectories. High In electrical and logic circuits the higher of two possible voltages, usually a control voltage. High density - HD A relative term applied to a disk's capacity. High density 3.5 inch floppies have a capacity of 1.44 Mb, twice the ST's norm. These are fitted as standard to all Mega STEs, TTs and Falcons. High-level language A programming language that does not reflect the structure of a particular computer or processor and thus can be used to write programs for different computers, such as C, BASIC, Pascal. High memory - HIMEM The upper addresses of the available RAM. High resolution A relative term used to denote the amount of pixels or dots on a screen. On the ST range it refers to the mono monitor resolution of 640 x 400 pixels, whereas the TT high resolution is 1,280 x 960 pixels. Highlight To emphasize text or other object, such as with reverse video or bold type. High-speed A data communications device capable of handling more than 4,800 bps. Hinting A special algorithm used for producing small point sizes from scalable fonts where the position of some of the dots making up a character is optimized for better results. See Scalable fonts. History file The continuous flow of data received during a communications link can be saved to a memory buffer and to disk. This file shows the 'history' of the transmission and is often more convenient to read off-line than the same data whilst on-line. Also, the term is synonymous with 'archive file'. Hit rate The number of successes in relation to the number of tries, such as in finding the relevant number of words of data in a RAM cache. HLL High-Level Language. Home The top upper left corner of a screen display. Horizontal tab - HT ASCII character 9 which moves the printing position or cursor a preset distance to the right along the line, commonly four or eight character positions in a monospaced font display. Host adapter A circuit board that interfaces the ST/STE's DMA port to an industry standard SCSI interface and which is usually embedded into the drive itself. Host computer/machine The controlling main computer in a communications system, the one that the terminals and other computers would log on to. Housekeeping Routines that perform some management operations on storage that don't concern the processing of data, such as copying, deleting, archiving files etc. Such processes normally 'tidy-up' the system keeping it at optimum performance. HP-GL Hewlett-Packard Graphics Language. A system for describing vector graphics drawings in a form which can be stored or output to a plotter or laser printer and devised by Hewlett-Packard. Now very much a standard and currently at version 2 (HP-GL/2). HTML HyperText Markup Language. The language used to create hypertext documents for use on a WWW server. Simple commands are added to a ASCII text file which provide links to graphic files, sound and other pages. HTML describes the structure of a WWW page, the server provides the layout. HTML+ is being developed which will provide more features. See WWW, Hypertext. HTTP HyperText Transfer Protocol. The transfer protocol used to transmit WWW hypertext pages across the Internet from a WWW/HTTP server to the remote client which displays them. Huffman compression A lossless file compression method based on the RLE algorithm that uses a dictionary to store the frequency of patterns of repeating data which is stored with the resulting compressed file. It is highly efficient on text, less so on images and produces better results than the RLE method. See Compression. Human-oriented language A programming language containing features similar to a natural language, such as BASIC. Hybrid computer A computer combining digital and analogue elements. Hypermedia A mixture of hypertext and multimedia, viewing hypertext documents whose links are video, film, sampled speech or music. See Hypertext. Hypertext A document containing highlighted or usually, underlined words, icons and pictures that link into other parts of the document, other documents or pictures. When a link is selected, usually with the mouse, you are shown that link and therefore you can progress through that document not in the usual linear fashion; from start to end; but taking any route that interests you. The Internet's World Wide Web and the shareware program ST-Guide use hypertext documents. Hyphenation The placing of a hyphen (-) where a word has been split at the end of a line and where it is not desirable to move the whole of that word on to the next line. Hz HertZ. H 63 entries EOF