Category:Sinclair ZX81 BASIC: Difference between revisions

Sinclair ZX81 BASIC is the dialect of BASIC resident in ROM on the ZX81 home computer (1981) and compatibles (Timex Sinclair 1000, Lambda 8300, and many others). It was developed by John Grant and Steve Vickers. Around 1.5 million ZX81s and 'official' compatibles were sold, together with a substantial number of clones (unofficial compatibles) manufactured in Brazil, Hong Kong, and elsewhere. Today, ZX81 emulators exist for a wide range of platforms and operating systems.

The ZX81 has no moving parts and only four microchips: the 3.25MHz Z80 CPU, an 8k ROM chip containing the operating system and BASIC, a 1k RAM chip, and an uncommitted logic array. Since there is no separate video chip, the CPU spends about 75% of its time driving the display and only 25% doing everything else. This can, however, be controlled under BASIC using the <code>FAST</code> and <code>SLOW</code> commands: <code>FAST</code> blanks the screen and allows the processor to operate at full speed, and <code>SLOW</code> reverts to the default behaviour. Even <code>FAST</code> mode can be slower than some other BASIC dialects running on comparable hardware, because ZX81 BASIC has no integer type: all numeric operations have to be done on 40-bit floats using software floating-point routines. If you are used to other popular 8-bit computers, you should expect the ZX81 to feel noticeably slower.

The original machine's 1k of RAM was shared between the display, the system variables and stack, and the user's program and variables. An expansion pack from Sinclair increased the RAM to 16k; other sizes were available from third parties, allowing the ZX81 to be expanded to a theoretical maximum of 56k. The Timex-branded modelmodels marketed in theNorth UnitedAmerica Statescame hadwith aeither minimum2k ofor 2k16k, as did many of the clones;. anMost expansionZX81 packBASIC wasprograms availableon fromRosetta SinclairCode towill increasework with the 1k configuration, but unfortunately some of them do require more. The minimum RAM requirement is usually stated in a note to 16k,the andprogram: expansionswhere ofit otheris sizesomitted, wereit producedcan bygenerally thirdbe partiesassumed to be 1k.