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The meaning of «zx80»

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 very popular straight away, and for some time there was a waiting list of several months for either version of the machine.

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

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. The ZX80 was designed around readily available TTL chips; the only proprietary technology was the firmware. The successor ZX81 used a semi-custom chip (a ULA or Uncommitted Logic Array) which combined the functions of much of the earlier hardware onto a single chip reducing the chip-count from 21 to 4. However this was mainly a cost-reduction effort;[6] the hardware functionality and system programs were very similar, with the only significant difference being the NMI-generator necessary for slow mode in the ZX81 (see ZX81 for technical details), and the 4K integer-only Sinclair BASIC upgraded to 8K floating-point-capable, with the upgraded ROM also available as upgrade for the ZX80. Both computers can be made by hobbyists using commercially available discrete logic chips or FPGAs.

The 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.[7]

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).

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".[8] 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, blank 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.[7] 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 (and vice versa); with 1 KB RAM, running a 990 byte program would result in only one row of characters being visible on the screen; a full screen (32×24) would leave only 384 bytes to the programmer.

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