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ZX80

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ZX80
TypeHome computer
Release dateUnited Kingdom: 29 January 1980
(44 years ago) (1980-01-29)
Introductory price£99.95 GBP (£541; $741 at 2024 prices)
Discontinued1981
Units shipped100,000[1]
MediaCassette tape
Operating systemSinclair BASIC
CPUZ80 @ 3.25-3.55 MHz (most machines used the NEC μPD780C-1 equivalent)
Memory1 KB (16 KB max.)
StorageExternal Compact Cassette recorder
DisplayMonochrome display on UHF television
Graphics24 lines × 32 characters or
64 × 48 block graphics mode
PredecessorMK14
SuccessorZX81

The Sinclair ZX80 is a home computer launched on 29 January 1980[2] by Science of Cambridge Ltd. (later to be better known as Sinclair Research). It is notable for being one of the first computers available in the United Kingdom for less than a hundred pounds. It was available in kit form for £79.95, where purchasers had to assemble and solder it together, and as a ready-built version at £99.95.[3][4]

The ZX80 was advertised as the first personal computer for under £100 and received praise for its value and documentation. However, it faced criticism for screen blanking during program execution, small RAM size, and the keyboard design. It was very popular straight away, and for some time there was a waiting list of several months for either version of the machine.

Name

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The ZX80 was named after the Z80 processor with the 'X' meaning "the mystery ingredient".[5]

Hardware

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Internally, the machine was designed by Jim Westwood around a Z80 central processing unit with a clock speed of 3.25 MHz, and was equipped with 1 KB of static RAM and 4 KB of read-only memory (ROM). It had no sound output.[6]

The ZX80 was designed around readily available TTL ICs, without any custom chips; the only proprietary technology was the firmware.[7][8]

The machine was mounted in a small white plastic case, with a one-piece blue membrane keyboard on the front. There were problems with durability, reliability and overheating (despite appearances, the black stripes visible on the top rear of the case are merely cosmetic, and are not ventilation slots).[9]

Video output was black-and-white, character-based.[10] However, the ZX80 character set included some simple block-based graphics glyphs, allowing basic graphics to be accomplished, with some effort. One advantage to using monochrome video is that different colour broadcast standards (e.g. PAL, SECAM) simply weren't an issue when the system was sold outside the UK.[11]

Display was over an RF connection to a household television, and simple offline program storage was possible using a cassette recorder. The video display generator of the ZX80 used minimal hardware plus a combination of software to generate a video signal. (Some say this was an idea popularised by Don Lancaster in his 1978 book The TV Cheap Video Cookbook and his "TV Typewriter".[12] However, that design didn't involve a microprocessor for video generation, and it wasn't really similar to the ZX80 in other aspects either. The ZX80 and ZX81 also employed very specific traits of the Z80 processor.)

Unlike the later follow up, ZX81, the ZX80 could only generate a picture when it was idle, i.e. waiting for a key to be pressed. When running a BASIC program, or when pressing a key during editing, the tv-display would therefore blank out (lose synchronisation) momentarily while the processor was busy. So a BASIC program had to introduce a pause for input to display the next change in graphical output,[10] making smooth moving graphics impossible. This could be overcome only by very clever machine code tricks. These had to effectively replace the video rountines in ROM and embed the same in the normal program logic with exact timing, which is extremely cumbersome. However, a few such games were developed by skilled users or programmers later on.

Firmware

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The 4 KB ROM contained the Sinclair BASIC programming language, editor, and operating system. BASIC commands were not entered by typing them out but were instead selected somewhat similarly to a programmable graphing calculator - each key had a few different functions selected by both context and modes as well as with the shift key.[10]

Expansion

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Upgraded ZX80 showing the ZX81-style replacement keyboard overlay for use with the 8K ROM

Other than the built-in cassette and video ports, the only provided means of expansion was a slot opening at the rear of the case, which exposed an expansion bus edge connector on the motherboard. The same slot bus was continued on the ZX81, and later the ZX Spectrum, which encouraged a small cottage industry of expansion devices, including memory packs, printers and even floppy drives. The original Sinclair ZX80 RAM Pack held either 1, 2 or 3 KB of static RAM[13] and a later model held 16 KB of dynamic RAM (DRAM).[14]

Following the ZX81's release, a ZX81 8 KB ROM was available to upgrade the ZX80 at a cost of around 20% of a real ZX81. It came with a thin keyboard overlay and a ZX81 manual. By simply taking off the top cover of the ZX80 and prying the old ROM from its socket and carefully inserting the new ROM and adding the keyboard overlay, the ZX80 would now function almost identically to the proper ZX81 – except for SLOW mode, due to the differences in hardware between the two models. The process was easily reversed to return the ZX80 to its original configuration.[15]

One common modification by hobbyist users was to attach a full-size keyboard, optionally moving the motherboard into a larger case. This had the dual advantages of making the machine easier to type on, while increasing ventilation to the motherboard.[16]

Versions

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The UK version of the machine was the standard, and only changes that were absolutely necessary to sell units in other markets were made. In fact, the only real change made in most markets involved the video output frequency (the ZX80 used an external power transformer, so differences in AC line frequency and outlet were not an issue to the machine itself). One outcome of this is that the machine had some keyboard keys and characters that were distinctly British: NEWLINE was used instead of ↵ Enter, RUBOUT instead of ← Backspace or DELETE, and the character set and keyboard included the Pound symbol.

Reception

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The ZX80 was widely advertised as the first personal computer for under £100 GBP[17] (US$200.[4][10]) Kilobaud Microcomputing liked the design of the preassembled version, and said that the screen flickering during input or output was annoying but useful as an undocumented feature, indicating the computer functioning correctly. It praised the documentation as excellent for novices, and noted that purchasing the computer was cheaper than taking a college class on BASIC. The magazine concluded, "The ZX-80 is a real computer and an excellent value", but only for beginners who could learn from the documentation or programmers experienced with writing Z-80 software.[18] BYTE called the ZX80 a "remarkable device". It praised the real-time, interactive BASIC syntax checking, and reported that the computer performed better on benchmarks than some competitors, including the TRS-80 Model I. The magazine criticised the screen blanking during program execution, small RAM size, inadequate built-in Sinclair BASIC, and keyboard, and recommended against buying the kit given difficulty of assembly and because purchasers did not save money. BYTE concluded that "the ZX80 might be summarized as a high-performance, very low-cost, portable personal computer system ... a good starting point".[10]

Sales of the ZX80 reached about 50,000, which contributed significantly to the UK leading the world in home computer ownership through the 1980s. Owing to the unsophisticated design and the tendency for the units to overheat, surviving machines in good condition are sought after and can fetch high prices by collectors.[19]

Clones

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There were also clones of the ZX80, such as the MicroAce,[20] and from Brazil the Nova Eletrônica/Prológica NE-Z80 and the Microdigital TK80.[21][22][23]

See also

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References

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  1. ^ Hayman, Martin (July 1982). "Interview – Clive Sinclair". Practical Computing. Vol. 5, no. 7.
  2. ^ "Sinclair ZX80 Launched". Centre for Computing History. Retrieved 23 December 2018.
  3. ^ "Advertisement for Sinclair ZX81". Practical Computing. Vol. 4, no. 4. April 1981. pp. 72–73.
  4. ^ a b "The first personal computer for under $200". BYTE (Advertisement). Vol. 6, no. 6. January 1981. p. 119. Retrieved 18 October 2013.
  5. ^ Tomkins, Stephen (11 March 2011). "ZX81: Small black box of computing desire". BBC News. Retrieved 11 March 2011.
  6. ^ Maunder, Bob; Trotter, Terry; Logan, Ian (1980). The ZX80 Companion (PDF). LINSAC. p. 7. Retrieved 29 December 2024. The [television] set should be tuned to channel 36 UHF by means of the normal tuning controls. There is no sound output so the volume should be set to minimum.
  7. ^ Sinclair Research Ltd. (1980). "Sinclair ZX80 assembly instructions" (PDF). Martinův 8-bitový blog. pp. 7–8. Retrieved 29 December 2024.
  8. ^ Maunder, Bob; Trotter, Terry; Logan, Ian (1980). The ZX80 Companion (PDF). LINSAC. p. 90. Retrieved 29 December 2024.
  9. ^ Tebbutt, David (April 1980). "Benchtest: The Sinclair ZX80". Personal Computer World. p. 55. Retrieved 29 December 2024. …the casing even has go-faster stripes, which look suspiciously like ventilation slots in black and white photographs (coincidence, I'm sure).
  10. ^ a b c d e McCallum, John C (January 1981). "The Sinclair Research ZX80". BYTE. Vol. 6, no. 6. pp. 94–102. Retrieved 18 October 2013.
  11. ^ Tebbutt, David (April 1980). "Benchtest: The Sinclair ZX80". Personal Computer World. p. 55. Retrieved 29 December 2024. American television (525 line) users are catered for as well; all they need to do is solder in one diode and the system is converted from 50 to 60Hz standards.
  12. ^ Adamson, Ian; Richard Kennedy (1986). "A New Means To An Old End". Sinclair and the 'Sunrise' Technology. Penguin Books.
  13. ^ "1 to 3K byte memory expansion RAM PACK for the Sinclair ZX80". F J Kraan. Archived from the original on 22 February 2013. Retrieved 8 December 2019.
  14. ^ "Ultra Rare Vintage Sinclair ZX80 16K Byte Ram Pack (Mint)". Ebay. Retrieved 14 December 2019.[dead link‍]
  15. ^ "Advertisement for ZX Printer". Your Computer. Vol. 1, no. 3. October 1981. pp. 42–43. Retrieved 13 December 2019.
  16. ^ "DK'Tronics advertisement for full sized keyboard". Your Computer. Vol. 2, no. 5. May 1982. p. 5. Retrieved 13 December 2019.
  17. ^ "ZX80". Planet Sinclair.
  18. ^ Wszola, Stanley J. (December 1980). "The Sinclair ZX-80 Microcomputer". Kilobaud Microcomputing. pp. 168–169. Retrieved 23 June 2014.
  19. ^ "Retro: Cash in on your vintage PC". Alphr. 7 October 2009. Archived from the original on 6 December 2021. Retrieved 25 November 2019.
  20. ^ Searls, Delmar (April 1981). "The MicroAce Computer". BYTE. Vol. 6, no. 4. pp. 46–64. Retrieved 18 October 2013.
  21. ^ NE Z80
  22. ^ "Microdigital" (in Portuguese). 1 January 2002. Archived from the original on 23 December 2017. Retrieved 1 July 2013.
  23. ^ "Clube do TK90X". www.tk90x.com.br. Retrieved 19 December 2022.
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