Alejandro Valero's Mercury Ace Is the Tricked-Out Jupiter Ace That Never Was

Vintage computing enthusiast Alejandro Valero has created a clone of the ill-fated Jupiter Ace microcomputer with a difference: it's boosted to specifications and features of which the original designers could have only dreamed, including high-resolution video and 528kB of user-accessible memory.

"Launched in 1982, Jupiter Ace is one of the least known personal computers of the domestic computing era. Even thought its commercial life was short and it never achieved the success of other contemporary system, those of us who saw the raise of personal computing in the '80s remember the Jupiter Ace as the machine with a novel approach, since it was based on Forth instead of BASIC," Valero explains.

"Nowadays," Valero continues, "more than four decades after, I've decided to create a clone which is aesthetically as close as possible to the original, without getting to the point of being an exact copy, by getting an understanding of the hardware to the point of allowing me to make modifications that add more power to it, and more importantly, to learn along the way."

The Jupiter Ace was a product of Jupiter Cantab, a Cambridge-based microcomputer company founded by Richard Altwasser and Steven Vickers to compete with the Sinclair ZX80 — built by their former employer Sinclair Research. The decision to use Forth when most rival machines of the era used BASIC, the availability of the far cheaper Sinclair ZX81, and the release of the full-color ZX Spectrum saw the Jupiter Ace fall by the wayside — and the company went bankrupt after just one year in operation.

Valero's Mercury Ace, then, is the Jupiter Ace that could have been — a fully-compatible clone, based on an existing design of Grant Searle and existing schematics, which offers a wealth of upgrades. The standard 1kB of user-accessible RAM has been boosted to a whopping, by 1980s standards, 528kB, split into 16kB on-board and 512kB in an add-on module, along with 32kB of text RAM and 32kB of character RAM; there's a high-resolution video mode, again by the era's standards, of 256×192; there's video shadow RAM support; and software-selectable ROM paging, all housed in a replica case.

Valero wasn't alone in the design: in addition to those mentioned above, Valero had assistance from Pedro Gimeno in designing the PCB and high-resolution add-on board, and Gimeno also the ROM; the case, meanwhile, is based on one released by Cees Meijer — with a few tweaks. The project also has the blessing of Paul Andrews, whose company acquired the rights to the Jupiter Ace in 2015.

More information on the project is available on Hackaday.io, while Valero has published everything you need to build your own in a Codeberg repository under the reciprocal GNU General Public License 3.