Jupiter Ace

The Jupiter Ace was a compact British home computer designed by former Sinclair engineers Richard Altwasser and Steve Vickers. Rather than following the market’s near-universal adoption of BASIC, it placed a complete Forth programming environment in ROM.

Forth’s compact compiled code made effective use of the Ace’s tiny standard memory and ran much faster than interpreted BASIC. The unconventional language, monochrome character graphics and limited commercial software restricted sales, but made the computer one of the era’s most distinctive designs.

Notable Features

• ACE Forth in ROM served as both programming language and interactive operating environment.
• All 128 display characters could be redefined for character-based graphics.
• Forth words could be compiled, listed, edited and saved as a dictionary to cassette.

Historical Significance

• Designed by key contributors to the ZX81 and ZX Spectrum after leaving Sinclair Research.
• One of the very few consumer computers supplied with Forth instead of BASIC.

Collector’s Notes

• Standard user RAM is 1KB; quoted 3KB totals include two dedicated video-memory banks.
• The membrane keyboard, RAM expansions and original Forth manual are central to a complete example.

Specifications

Technical Information
Name	Jupiter Ace
Manufacturer	Jupiter Cantab
Launched	Wednesday, September 22, 1982
Discontinued	1984
Launch Price	£89.95
Country	United Kingdom
CPU	Zilog Z80A at 3.25 MHz
Units Sold	Approximately 5,000
Operating System	ACE Forth based on the Forth-79 standard
I/O	Cassette, television and expansion connectors
Keyboard	Integrated 40-key membrane keyboard
Storage	Approximately 1500-baud cassette
Sound	CPU-driven internal speaker
Graphics	128 redefinable 8 x 8 characters and semigraphics
Display	32 x 24 monochrome characters
ROM	8KB containing ACE Forth
RAM	1KB user RAM plus 2KB dedicated video memory; expandable to approximately 49KB
CPU Speed	3.25 MHz