Jupiter ACE

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The Jupiter ACE was a British home computer of the 1980s, marketed by a company named Jupiter Cantab and named after the early British computer, the ACE. The company was formed by Richard Altwasser and Steven Vickers, who had been on the design team for the Sinclair ZX Spectrum.

The Jupiter ACE somewhat resembled a ZX81 in a white case, with black rubber keys like the Spectrum. It displayed output on a television, and programs could be saved and loaded on cassette tape, as was standard at that time. The machine was based on a Zilog Z80 processor clocked at 3.25MHz, and came with 3 kB RAM, expandable to 49 kB. While it had only one video mode, text only, which displayed 24 rows of 32 columns of characters in black and white, it was possible to display graphics, by redefining the 8×8 pixel bitmap of any of the 128 characters. Like the ZX Spectrum, the machine's audio capabilities were restricted to beeps of programmable frequency and duration, output through a small built-in speaker.

Although the hardware, and to some extent the software, of the ACE was similar to the ZX81 and in particular the ZX Spectrum, unlike those machines it used discrete transistor-transistor logic rather than the ULAs of the Sinclair machines. The font of the character set was identical to that of the Spectrum, but again unlike the earlier machines, the display was white on black. Unlike the ZX81, the display was generated by hardware. Like the Spectrum, the keyboard was of the rubber-keyed or 'chiclet' variety, but there was no single-keyword entry. The case and speaker were also very similar, although there was an extra interface for the attachment of a colour graphics board that was never produced.

The major difference from the 'introductory computer' that was the ZX81, however, was that the Jupiter ACE's designers, from the outset, intended the machine to be for programmers: the machine came with Forth as its default programming language. The dialect of Forth used on the ACE was based on Forth-79 rather than FIG-Forth, although it deviated somewhat from it in various ways. In particular, screens were not used and the editor was like the Sinclair one rather than the original Forth editor. An interesting innovation is that it did not store the text of the Forth program (as in other Forth systems) but compiled the code after editing and stored it in ready-to-run format. When you edited a word, it would then decompile the code on-the-fly back into text for editing. This saved memory space and also time in reading and writing programs from cassette tape. The ACE had an 8K ROM containing the O/S, Forth Kernel and the predefined dictionary of Forth words. Some of the ROM was written in Z80 machine code, but some was also coded in Forth, giving it very elegant self-referential operating system.

Several words were borrowed from Sinclair Basic. Though Forth gave a great speed advantage over the interpreted BASIC that was used on other machines, it did, along with the meager sound and graphics capabilities compared to the upcoming competition, kept the ACE squarely in a niche market. Sales of the machine were never very large; as of the early 2000's, surviving machines are quite uncommon, fetching quite high prices as collectors items.

External links

Sinclair computers, derivatives, and clones (ZX80/81, ZX Spectrum, and QL clones)

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