The ZX80 was sold on its price. Sinclair’s own advertising called it the “world’s first complete personal computer for under £100”: £99.95 ready built, or £79.95 as a kit of parts to solder together at home. Your Computer later put the going rate for a personal computer at the end of the 1970s at around £300. For Sinclair’s money you got a plastic case about the size of a hardback book, a touch-sensitive keyboard, 1K of memory and a BASIC that fitted in 4K of ROM. You supplied the television and the cassette recorder.
It was not a comfortable machine to use. It could count only in whole numbers, and it could not draw the picture and run a program at the same time, so the screen went blank whenever it was busy. It was still a clever piece of design. The ZX81 and the ZX Spectrum both grew out of it, and both kept its best idea: you typed a BASIC keyword with one keypress, and the computer checked every line before it let you enter it.
Fast facts
- Launch: shown at an exhibition in Wembley at the end of January 1980, on sale by mail order in February 1980.
- Price: £79.95 as a kit, £99.95 built. In the United States it sold by mail order for $199.95 assembled.
- CPU: NEC 780-1, a copy of the Zilog Z80, at 3.25 MHz.
- RAM: 1K of static memory, expandable to 16K.
- ROM: 4K, holding the BASIC interpreter, the operating system and the character set.
- Display: 24 lines of 32 characters, black on white, through the aerial socket of a television.
- Keyboard: 40 touch-sensitive keys on a sealed membrane.
- Storage: cassette tape.
- Hardware design: Jim Westwood. Software: John Grant of Nine Tiles.
Who made it
Clive Sinclair told the American magazine Creative Computing in 1980 that work on the ZX80 “started in March 1979 and it was put on the market in February 1980”. Very few people were involved, he said: he had the original idea, two or three engineers worked on the detail, “one engineer in particular did the final design and one wrote the software”.
The engineer was Jim Westwood. David Tebbutt’s review of the machine for Personal Computer World, reprinted in Creative Computing in December 1980, thanks “Jim Westwood (its designer)” for answering his questions. Tebbutt had been lent a development machine, with a couple of EPROMs on stripboard wired into the ROM socket, and “thought it best to spare Mr. Sinclair’s blushes” by printing no pictures of its insides. A later Sinclair Research staff profile credits Westwood with the project management and the development of the ZX80’s hardware and display system. Westwood had joined Sinclair Radionics in 1963, and went on to design the ZX81’s custom chip.
The software came from outside. Sinclair commissioned the BASIC from Nine Tiles, a Cambridge software firm, where John Grant wrote it. Your Computer reported in 1986 that work on it had begun in April 1979, and that Grant’s ZX80 software was “generally recognised” as “a masterpiece of efficient and economic coding”. It was loosely based on the ANSI Minimal BASIC standard, and Grant set out to fit in as much of it as the 4K would allow. Nine Tiles went on to write the ROMs of the ZX81 and the Spectrum, where Steven Vickers did most of the work.
The case came from John Pemberton, Sinclair’s industrial designer at the time. Rick Dickinson, who took over from him, recalled in 2004 that his first job was to put “John Pemberton’s design for the ZX80 into production”, and that the case parts were vacuum formed because Sinclair “didn’t have the financial muscle to lay down expensive tooling”.
Typing it in
The ZX80’s BASIC is the part that impressed reviewers. Keywords did not have to be spelled out. Press the key marked with PRINT at the start of a statement and the whole word appeared, stored in memory as a single byte. A cursor showed what the computer expected next: an inverse K for a keyword, an L for anything else.
The interpreter also checked every line as it was typed. If it could not make sense of what you had written, it showed an inverse S (for syntax) at the point where it thought you had gone wrong, and refused to accept the line until you fixed it. Tebbutt called the syntax checking “superb — it’s impossible to go wrong”, and added: “What a grown up facility for such a small machine!” John McCallum, reviewing the ZX80 for BYTE in January 1981, wrote that he had “always been disappointed that most other versions of BASIC do not do this”. He also found that it applied the same checks when a running program asked you for input, so the ZX80 never gave you the string errors “so common with other personal computers”.
The keyboard itself divided opinion. It was a flat plastic sheet over contacts, sealed against spills. Tebbutt found that typing on it “gives a sensation of drumming your fingers rather than of doing anything useful”, then decided this was “a totally mistaken impression because it really works rather well”. McCallum struggled to hit the shifted keys without pressing an extra one by mistake, and kept ending up with zeros where he had meant to delete a character. He thought that saving money on the keyboard was still the right choice: “some people pay more for a keyboard than this entire computer costs”.
Whole numbers only
The 4K ROM had to hold the interpreter, the character set, the keyboard routines and the cassette routines, so the BASIC was small. It handled only whole numbers between −32768 and 32767. Divide 13 by 5 and you got 2. There were no floating-point numbers, no trigonometry, and no way to join two strings together. Programs and their data could only be saved to tape together, as a single file.
The vanishing picture
The ZX80 has no video chip. The Z80 processor draws the picture itself, helped by a few standard logic chips, and while it is drawing the picture it cannot do anything else. Sinclair’s designers made the processor do one job at a time: whenever it has other work to do, it stops drawing the picture. The screen goes blank while a program runs, while you type, and while it loads or saves a tape.
McCallum called this “the most limiting characteristic of the ZX80”. It ruled out the moving games of a PET or an Apple II. It had one benefit he could see: “when performing long calculations on the ZX80, it is easy to tell when the program ends — the room bursts into light!” Tebbutt found that the brief flicker as each key went in was useful, because it showed that the key had registered. The authors of The ZX80 Companion, a guide to the machine published in 1980, said the same.
For all that, the ZX80 ran BASIC quickly. McCallum ran a set of standard BASIC benchmarks, and the ZX80 came between second and third among the machines they had been run on. Only a 2 MHz 6502 system and a 4 MHz Z80 system beat it. Among the computers it beat was the TRS-80 Model I.
Selling it
According to Rodney Dale’s history of the company, published in Sinclair User in 1986, ten orders were placed at the Wembley exhibition in the first five minutes. The office in Cambridge was soon “inundated with cheques” and its switchboard “permanently jammed”. Over 20,000 had been sold by September 1980. By the following year Sinclair’s advertisements were saying that “over 50,000 were sold”. Alessandro Grussu’s Spectrumpedia, a modern history, puts the final total at more than 100,000.
Sinclair sold the ZX80 by post rather than through shops, from Cambridge and, for the United States, from an office in Boston run by Nigel Searle. BYTE noted that the American price had fallen from an expected $245 to $199.95 by the time the machine arrived there in autumn 1980.
A whole trade in add-ons grew up around it. The first add-ons were memory. Sinclair sold its own 1K to 3K RAM packs, Dickinson’s first job, followed in September 1980 by a 16K pack. The packs plugged into the edge connector at the back of the machine, and CRASH later recalled that pressure on the keyboard could rock them, and that quite a few machines failed when the connectors shorted. The problem went on to become famous on the ZX81. Other companies, dk’tronics and Quicksilva among them, began by selling memory for the ZX80.
The 8K ROM and the ZX81
Sinclair announced a new 8K BASIC for the ZX80 at the Personal Computer World Show in London in September 1980. It was a plug-in replacement for the original ROM, with a new keyboard overlay. The ZX80 Companion, going to press as it was announced, described a prototype that added floating-point arithmetic, scientific functions, string arrays, named files on tape and simple graphics commands.
The ROM Sinclair went on to sell was the BASIC of the ZX81, which arrived in March 1981: Sinclair User later described it as an add-on “to convert the ZX80 to the ZX81”. Sinclair’s order forms were still offering it for £19.95 in 1982. The ZX81 put most of the ZX80’s chips into a single custom chip, cost £69.95 built or £49.95 as a kit, and could keep the picture on the screen while a program ran. A new ROM could not give the ZX80 that last feature, and other companies sold kits that did. One advertisement promised “the full animated graphics of the ZX81 (No screen flicker!)” for £12.95 in kit form, for use only with the new ROM.
By late summer 1981, Your Computer‘s buyers’ guide listed the ZX80 as “now available second-hand”.
Sources
- Creative Computing, vol. 6 no. 12, December 1980: David Tebbutt’s review of the ZX80, reprinted from Personal Computer World (pp. 28–34): the NEC 780-1 at 3.25 MHz, the blanking display, the keyboard, the syntax checking, the development machine he was lent, and the thanks to “Jim Westwood (its designer)”. David Ahl’s interview with Clive Sinclair (p. 108): the development dates, the size of the team, and selling by direct mail in Britain and the United States.
- John C. McCallum, “The Sinclair Research ZX80”, BYTE, January 1981, pp. 94–102: the $199.95 price and American availability, single-keystroke keywords, syntax checking, screen blanking and “the room bursts into light”, the keyboard, the 4K ROM’s contents and missing functions, and the benchmark results. The review names the manual as Hugo Davenport’s A Course in BASIC Programming.
- Bob Maunder, The ZX80 Companion, 2nd edition (Linsac, 1980): the input range −32768 to 32767 (p. 11); whole-number division (p. 32); the NEC 780-1, the 3.25 MHz clock and the blanking display (pp. 83–84); the 8K ROM’s launch at the Personal Computer World Show, 4–6 September 1980, and its new features (pp. 122–124).
- Sinclair User issue 46, January 1986, pp. 85–87: extract from Rodney Dale’s The Sinclair Story: the Wembley launch at the end of January 1980, the Z80A from Nippon Electric, the first orders, over 20,000 sold by September 1980, Nigel Searle’s Boston office, and the 16K RAM pack in September 1980.
- Your Computer, August/September 1981: news report on the February 1980 launch (p. 19); Sinclair ZX81 advertisement, “At £99.95, the ZX80 offered a specification unchallenged at the price. Over 50,000 were sold” (p. 40); buyers’ guide (p. 68).
- Your Computer, January 1986, “Knight-clubbing”, by Ian Adamson, Richard Kennedy and Freda Trovato: work on the BASIC from April 1979, John Grant’s software, and the ANSI Minimal basis.
- Your Computer, January 1982 and February 1982: third-party advertisements for kits adding ZX81-style display to a ZX80 with the 8K ROM. Your Computer, March 1982: Sinclair order form offering the 8K BASIC ROM for the ZX80 at £19.95.
- CRASH issue 16, May 1985, p. 126, “The Sinclair Story”: prices of “£80 in kit form” and £100 built, whole numbers only, programs and data saved together, the RAM pack problem, and dk’tronics and Quicksilva.
- Edge issue 137, June 2004, pp. 80–83: interview with Rick Dickinson, on John Pemberton’s design, the vacuum-formed case parts, and the RAM packs.
- Alessandro Grussu, Spectrumpedia, volume 1 (English edition, CC BY-NC-ND 4.0), p. 18: £79.95 kit and £99.95 built, “more than 100,000 units” sold before production ended in August 1981; pp. 70–71: a Sinclair Research staff profile of Jim Westwood.