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A PROGRAM which appears to defy the rules of mathematics has been added to the Video Software range of 'serious' software for the ZX-81. Called Video-Index, the maths-defying element is the fitting of 57,000 characters of data in a 16K memory, which is achieved by an ingenious technique whereby duplications of descriptions are detected and eliminated.
Written largely in machine code for speed, VideoIndex provides a technique for using the ZX-81 to build a catalogue or index which can be stored on cassette and re-used. The program, which is supplied with a demonstration index of computer magazine articles about the ZX-81, costs £9.95 and can be obtained from Video Software, West Midlands.
A CASSETTE with 10 games to run on the ZX-81 with 16K RAM offers a wide choice. Recorded on both sides, the cassette offers all 10 games twice but in a different order, depending on the side of the cassette used.
The games include board and card games such as Othello and Pontoon and combat games such as Laser Bases.
It also offers Rectangle, where the object is to form rectangles with a bigger total area than those formed by the computer. The skill in this game is to form rectangles which are fairly big without having them blocked and at the same time to use your points to block the rectangles the computer tries to make.
The user and the computer take turns to choose a point, neither knowing which points the other has chosen until one calls 'show'. The games, assembled on the Cassette Two which costs £5, are available from the Michael Orwin ZX-81 Software Catalogue, London.
Orwin is putting together Cassette Three, which includes a game called Princess of Kraal, wherein the princess has to be rescued from a dungeon six levels deep and where you, the rescuer, having chosen the level of difficulty, time period of the game and type of maze, find your way to the correct room via perils including rockfalls, monsters and floods. There are some bonuses on the way but the princess is undoubtedly difficult to find.
A VERSION of Galaxians, the popular arcade game, is now available to ZX-81 users through W H Smith. Called predictably ZX-Galaxians, it requires 16K of RAM and offers personalised high-scoring routines, swooping attackers, full explosions and continuous status reports.
The originators, Artic Computing, believe that it was chosen by W H Smith because it is exceptional. Written in machine code, the game runs smoothly with no flicker on the screen, mostly because it uses pixels which split the characters in two.
W H Smith is selling Galaxians on a cassette at £4.95, which includes a dungeons and dragons random adventure game, Swords of Peace. Artic Computing can be contacted at Hull, North Humberside.
AN EFFECTIVE tool for the speedy development of Z-80 machine code routines entails a number of procedures which will facilitate loading, as well as check and query errors. Developed by Michael Cox Information Services, the M/C Load and M/C Edit programs form a suite which retails at £8.90 and is intended for use with a fully-debugged machine code program.
The procedures require you to draft your routine manually, listing Assembler mnemonics and, for the instruction codes, the relevant hex code. Using M/C Load, you then enter hex and decimal arguments to derive the ZX-81 code, which is added to the manual draft.
Using M/C Edit, the ZX81 code is entered together with break-points as required. So, when the routine is proved, the M/C Load program is used to enter the finished routine in memory.
MCIS can be contacted at North Weald Bassett, Essex.
ANOTHER GAME for the soon-to-be-released Michael Orwin Cassette Three requires 16K of memory and will be one of 10 or so games on the cassette. Starship Trojan puts you in the unfortunate position of being the only survivor on a starship which has been badly damaged in a meteor storm. It is satisfactory to be a survivor but you have to repair the damage to the ship before the total air level drops below 3,000 units and you only have 70 hours for repairs before your next inter stellar jump.
There are other dangers lurking but at least you are armed with lasers and stun grenades. The game promises to be at least as absorbing as previous Orwin cassettes and will be available from Michael Orwin, London.
A SYSTEM which enables you to keep detailed records of bank transactions and thus produce a better statement than that of your bank can is available to users of the ZX-81 16K RAM system. Personal Banking System offers facilities such as automatic posting on the statements of all standing orders due monthly, quarterly, six-monthly or annually and incorporates a machine code load/save feature which permits the storing of transactions in data files on cassette, separate from the program. That facility saves and loads the program variables only.
The Personal Banking System is available for £9.95 inclusive of cassette and user manual from J P Gibbons, Kent.