ZX80

ZX80

Type	Home computer
Release date	1980
Introductory price	£99.95 (in 1980)
Discontinued	1981
Media	Cassette tape
Operating system	Sinclair BASIC
CPU	Z80 @ 3.25 MHz (most machines used the NEC μPD780C-1 equivalent)
Memory	1 KB (16 KB max.)

The Sinclair ZX80 was a home computer brought to market in 1980 by Science of Cambridge Ltd., until 1977 known as Sinclair Instrument and later to be better known as Sinclair Research. It was notable for being the first computer (unless you consider the MK14) available in the United Kingdom for less than a hundred pounds (£99.95). It was available in kit form, where purchasers had to assemble and solder it together, and as a ready-built version at a slightly higher cost for those without the skill or inclination to build their own unit. The ZX80 was very popular straight away, and for some time there was a waiting list of several months for either version of the machine.

Description

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 containing 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 on a scientific calculator - each key had a few different functions selected by both context and modes as well as with the shift key.

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. This was an idea that was popularised by Don Lancaster in his 1978 book The TV Cheap Video Cookbook and his "TV Typewriter". As a result of this approach 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 even when pressing a key for any input, the display would, therefore, black out momentarily while the processor was busy. This made moving graphics difficult since the program had to introduce a pause for input to display the next change in graphical output. The later ZX81 improved on this somewhat because it could run in a "slow" mode while creating a video signal, or in a "fast" mode without generating a video signal (typically used for lengthy calculations). Another issue was that the main RAM was used to store the screen display, with the result that the available screen size would gradually decrease as the size of a program increased - with 1KB RAM, running a 990 byte program would result in only one row of characters being visible on the screen.

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. 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 get the ZX80 back to its old self.

Sinclair also produced RAM expansion packs for the ZX80; the original ZX80 RAM Pack held either 1, 2 or 3 KB of static RAM, a later model held 16 KB, using dynamic RAM chips (DRAM).

The machine was mounted in a tiny white plastic case, with a one-piece blue membrane keyboard on the front; it owed its distinctive appearance to industrial designer Rick Dickinson. There were problems with durability, reliability and over-heating (despite appearances, the black stripes visible on the top rear of the case are merely cosmetic, and are not ventilation slots).

Reception

Sales of the ZX80 reached about 50,000 — an unheard of number for the day 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 quite uncommon and can fetch high prices by collectors.

Hardware

The ZX80 was designed around readily available TTL chips; the only proprietary technology was the firmware. While the successor ZX81 used a semi-custom chip (a ULA or Uncommitted Logic Array), this merely combined the functions of the earlier hardware onto a single chip — the hardware and system programs (except the BASIC versions) were very similar, with the only significant difference being the NMI-generator necessary for slow mode in the ZX81. (See ZX81 for technical details.) Both computers can be made by hobbyists using commercially available discrete logic chips or FPGAs.

The primary audience for such computers at the time was hobbyists, and the ZX80 was primarily marketed towards that end. In the US, the ZX80 was available in two forms: a prebuilt unit for US$199.95, or a "kit" version, which provided all the parts but required assembly, for US$149.95. Capitalizing on the price, the system was advertised (in computing and electronics magazines) with the slogan "The first personal computer for under $200".

Clones

There were also unauthorised clones of the ZX80, namely the MicroAce (produced in the USA), and from Brazil the Nova Eletrônica/Prológica NE-Z80 and the Microdigital TK82.

External links

• Planet Sinclair:ZX80
• Review of Sinclair ZX80 from 1980
• Showcase of Sinclair ZX80