Jupiter Ace

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The Jupiter Ace was a British home computer of the early 1980s, produced by a company, set up for the purpose, named Jupiter Cantab. The Ace differed from other microcomputers of the time[1] in that it used FORTH instead of the more common BASIC.



Jupiter Cantab was formed by Richard Altwasser and Steven Vickers.[2] Both had been on the design team for the Sinclair ZX Spectrum. Altwasser did some work on the development of the ZX-81 and in the design of the hardware of the Spectrum. Vickers adapted and expanded the 4K ZX-80 ROM to the 8K ZX-81 ROM and wrote most of the ROM for the Spectrum. The Jupiter Ace was named after the early British computer, the ACE. The name was chosen to emphasize the "firsts" of using the FORTH language as more efficient for personal computers.

FORTH is a threaded code programming language that also acted as operating system. The system was adapted to the disk-less tape-using home computer hardware. On average, and for similar programs, ACE's FORTH was 5 times faster and used half the memory (which was a costly luxury at the time) of an equivalent program written in interpreted BASIC.[3] Forth programs tend to be more memory efficient than the bigger programs; as they become bigger, they reuse more previously-defined code.[4]

For such reasons FORTH was chosen to deliver better performance and [structured programming] flexibility.[5]

System characteristics

The Jupiter ACE is often compared with ZX81 due to its similar size, low cost, and similar form factor[who?], although internally it is an independent design. The ZX81 used 75% of its Z80 CPU time to drive the video. In ACE the Z80 CPU was fully used for running programs. The ACE used dedicated video memory of 2 KB, leaving the 1 KB main memory free for user programming.

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