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.
Introduction
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 FORTH environment as more efficient for personal computers. FORTH is a threaded code programming language that also acted as operating system.
Differently from previous introductory computers and being its major characteristic, its default programming language was Forth. Forth was considered well adapted to microcomputers (with small memory and relatively low-performance processors) for being fast. About 10 times faster than BASIC,[3] added to allow implementation of machine code routines, if needed for a particular task. And for embodying structural programming concepts found in Pascal Language.
For such reasons it was designed with FORTH, chosen to deliver better performance and Structured Programming flexibility.[4]
System characteristics
A small Jupiter ACE system
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.
The Jupiter ACE was new to the market and the designers couldn't afford to use an uncommitted logic array (ULA), a design approach then gaining popularity in other computers (such as the ZX 81) to reduce component count, because these weren't economical in small quantities. Instead they reduced the number of chips required via clever design.
Like the Spectrum, the Ace used black rubber keys. Audio capabilities were CPU controlled with programmable frequency and duration. Sound output was through a small built-in speaker. A television was needed as a display - which was in black and white only.
ACE's FORTH was "ten times faster than Basic"[5] (a reference to ACE FORTH),[6] and used less than half the memory (which was a costly luxury at the time) of an equivalent program written in interpreted BASIC.[7] Forth programs tend to be more memory efficient than the bigger programs; as they become bigger, they reuse more previously-defined code.[8]
Control structures could be nested to any level, limited only by available memory. It also allowed recursive programming, if desired. Programs and data storage was by means of a common cassette tape, which was typical of home computers of the time.
Specifications
- Processor: Zilog Z80A clocked at 3.25 MHz.[9]
- Memory: 1 KB, expandable up to 49 KB (Video SRAM excluded).
- Video: Independent sub-system using dedicated 2 banks of 1 KB making a total of 2 KB of extra SRAM.
- Sound: Internal Speaker.
- Keyboard: 40 keys.
- Expansion: 2 connectors: One CPU related similar to the one in the ZX-81, the other connecting to the Video sub-system.
References to the ACE RAM usually include the separate 2 KB video memory, which is not available for user programs, thus leading to some confusion.
Hardware
- Video
One 1K bank allowed redefinition of most of its 128 ASCII based characters in 8×8 pixel bitmap format. The other 1K bank stored the full screen display of 24 rows x 32 columns of characters in black and white. So while the Ace had only one text video mode, redefinition of the character shapes could provide graphics in a low resolution of 64x48, and a higher resolution mode of 256x192 graphics, limited by the 128 available (definable) 8x8 chars. Both graphics and text could be displayed at the same time.
The font of the character set is identical to that of the Spectrum, but the display is white on black whereas the Spectrum has colour hardware. Although a colour graphics board was designed[10] none was ever produced commercially.
- Sound
An internal speaker was directly controlled by the CPU in single task mode, with control of sound frequency and its duration in milliseconds.
- External Storage
Storage was through a cassette tape interface at 1500 baud.
- Add-ons
Originally developed to receive ZX-81 add-ons, with a compatible expansion slot, it was actually delivered in a different configuration. A simple rewiring adapter could be used, but not very effectively due to power losses. Dedicated add-ons were needed and built by external companies, after the initial 16 KB by Jupiter Cantab.
- RAM[11]
- Pack 16 KB by Jupiter Cantab.
- Pace 16 KB and 32 KB by Stonechip Electronics.
- Pack 48 KB by Boldfield (new Jupiter ACE owner after Jupiter Cantab).
- Keyboard[12]
- Memotech Keyboard, by Memotech.
- Sound[13]
- SoundBoard (1983) by Essex Micro Electronics,
- Storage[14]
- Jet-Disc Disc Drive System (1983) by MPE (control up to four 3", 5", or 8" drives).
- "Deep Thought" Disc interface with a 4K AceDOS in an EPROM (1986) by J Shepherd & S Leask.
- Printer Adapters
- ADS Centronics Interface Machine (1983), by Advanced Digital Systems,[15]
- RS232 & Centronics PrinterCard (1984) by Essex Micro Electronics.[16]
- Graphics Card
- Gray Scale card - 4 shades of gray by S Leask (1986)
Firmware
The ACE had an 8 KB ROM containing the Forth kernel and operating system, and the predefined dictionary of Forth words in about 5KB. The remaining 3KB of ROM were used for tape control, floating point numbers library and character definitions table.[17] Some of the ROM was written in Z80 machine code, but some was also coded in Forth.
The next 8 KB were split in 2 blocks of 4KB each. The video subsystem access allowing two different priorities by the user to the 2KB VRAM, Regular or Overriding video. The 1 KB of user RAM was only partially decoded, so it echoed in the full 4 kB block address space it resides. So a 16 KB space was used for ROM, VIDEO, and USER, leaving free a 16 KB space for RAM extension plus 32KB space free for all possible usages.
ACE's Forth
ACE's Forth was based mostly on Forth-79, with some relevant differences.[18] Runtime error checking could be turned off to raise speed by 25% to 50%. A few extra words were named similar to known BASIC sound, video and tape commands, as behavior was the same. The implementation lacked less frequently used Forth words, but these were easily implemented if needed.
The ACE's dialect of FORTH introduced several innovations. It simplified usual Forth definer and compiler words creation, replacing the CREATE .. DOES>,[19] creation pair with:
- DEFINER .... DOES> : Create new Defining words, usually used to define and build data data structures. Similar to CREATE..DOES usage in standard FORTH.[20] ( Examples: Arrays, Records, ... ).
- COMPILER .. RUNS> : Create new Compiling words, less frequently used to extend the language with compiler words where CREATE..DOES> is FORTH implementation dependent.[21] ( Examples: control structures like Case, Infinite-Loop, ... ).
As an operating system, it was adapted to Tape usage, saving/loading user vocabularies instead of the usual numbered programming blocks used in diskette systems. As FORTH programming environment, it added syntax checking to control structures and definer constructions.
The ACE's Forth could decompile its programs, unlike usual Forth systems. This decompiling ability had several advantages as a solution to the absence of the more flexible disk system used by Forth. It did not store the text of a Forth program, instead it compiled the code after editing and stored it in ready-to-run format. While this saved computer memory it also saved time in reading and writing programs from cassette tape. This tape-friendly and RAM-saving solution was unique to the Jupiter ACE Forth.
Finally, its FORTH was adapted to the disk-less tape-using home computer hardware.
Commercial
Though Forth delivered several advantages over the interpreted BASIC used on all other contemporary home computers, the weak box and small initial memory kept the sales low despite technical interest.[22]
Models
1982 - Original Jupiter ACE in a yogurt-pot type of case - Reported 8000 units built.[23]
1983 - Jupiter ACE 4000 on stronger injection moulded case - Reported 800 units built.[24]
Sales
Sales of the machine were never very large; as of the early 2000s, surviving machines are quite uncommon, fetching high prices as collector's items. One main reason for low sales seems to have been the need to buy an extra 16 KB RAM-extension which almost doubled the ACE's price. It happened that the designed 4 KB of base RAM was not built in favour of the less costly 1 KB delivered. The absence of colour kept the ACE squarely in a niche market of programming enthusiasts.
References
- ^ "Sales Brochure". http://www.jupiter-ace.co.uk/advert_J CSB_1.html. Page1
- ^ "An interview with Richard Altwasser and Steven Vickers". http://www.sincuser.f9.co.uk/004/newb iz.htm.
- ^ "The Complete FORTH", by Alan Winfield, 1983, Sigma Technical Press, page xi
- ^ "Electronics & Computing - Jupiter Ace Review, 1982, November", page 70
- ^ "Popular Computing Weekly(26August1982): Spectrum team deal their Ace". http://jupiter-ace.co.uk/news_pcw8207 2600005.html.
- ^ "Benchmarks (Entry #9)". http://jupiterace.proboards.com/index .cgi?action=display&board=presoth er&thread=315.
- ^ Popular Computing Weekly, 1982, August, 26: Spectrum team deal their Ace
- ^ James, John S.: "Byte Magazine, 1980, Aug. - What is Forth?", page 102, "Characteristics of FORTH Code" section
- ^ . p. 40. ISBN 978-84-689-9280-8. "Micro Z80 a 3.25 MHz [...], el Jupiter Ace [...]"
- ^ "Adding colour to the Ace". http://www.jupiter-ace.co.uk/hardware _colour_board.html. article in ETI Magazine, April 1984
- ^ "RamPacks". http://www.jupiter-ace.co.uk/hardware _rampacks.html.
- ^ "Memotech Keyboard". http://www.jupiter-ace.co.uk/hardware _memotechKboard.html.
- ^ "EME AY-3-8910 Sound board Review". http://www.jupiter-ace.co.uk/review_s oundcard.html.
- ^ "Disc Drives". http://www.jupiter-ace.co.uk/hardware _JetDisc.html.
- ^ "ADS Centronics". http://www.jupiter-ace.co.uk/hardware _ads_centronics_review.html.
- ^ "Printercard". http://www.jupiter-ace.co.uk/hardware _printercard.html.
- ^ "ACE ROM Project (E-Book)". http://factor-h.net/_extra/ace_rom_pr oject.zip.
- ^ Vickers, S: "Jupiter ACE Manual", page 176, 1982.
- ^ Winfield, Alan: "The Complete Forth", Chapter 9 "Extending FORTH", Sigma Technical Press, 1983.
- ^ Vickers, S: "Jupiter ACE Manual", page 120, 1982.
- ^ Vickers, S: "Jupiter ACE Manual", page 136, 1982.
- ^ "Jupiter ACE Reviews". http://www.jupiter-ace.co.uk/reviews. html.
- ^ "What is A Jupiter ACE". http://www.jupiter-ace.co.uk/whatisan ace.html.
- ^ "What is A Jupiter ACE 4000". http://www.jupiter-ace.co.uk/ace4000. html.
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