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S > SINCLAIR  > ZX 81   

ZX 81

The Sinclair ZX 81 was the successor of the ZX 80, and can be regarded as an evolution of it.

The ZX80 could not handle floating point numbers or cassette data files, but the ZX-81 could. The ZX-80 had 4k ROM : the ZX-81 had 8K ROM with 30 additional functions and some instructions to drive the printer. Thanks to a higher level of integrations (the total number of chips in the basic system was 4, against the ZX80's 21), the ZX-81 cost £30 less than the ZX-80. The plastic case was also different. Whereas the ZX-80 looked cheap in it lightweight white case, the ZX-81 was beautifully designed in its black ABS plastic case.

The keyboard was still formed by an underprinted plastic, but this one was made of non-reflective material. Even with this slight improvement it was quite horrible to use, that's why a lot of additional keyboards appeared quickly on the market. Some of the keys sported up to 5 functions, right in the Sinclair tradition, accessible through the "GRAPHICS", "SHIFT" and "FUNCTION" keys.

Here are the functions added over the ZX-80 : ASN, ACS, ATN COS, EXP, INKEY$, PI, SGN, SIN SQR, INT, LEN, LN, TAN, VAL, <=, >=, < >, COPY, DIM A$, FAST, FOR ... TO ... STEP, LLIST, LLIST n, LPRINT, PAUSE, PLOT, PRINT AT, PRINT TAB, SCROLL, SLOW, UNPLOT. Some are quite useful and make you wonder how it was possible to make anything on the ZX-80 !? However, one function disappeared: TL$ which was used to return a string minus its first character.

The ZX-81 could be operated in two modes, SLOW and FAST. The FAST mode which was the only mode available on the ZX-80, only refreshed the display when the system had completed computing, resulting in a painful screen flicker! It was a useful mode when you had to do a lot of calculation without the need to see what's going on all the time on the screen. The SLOW mode, which was indeed quite slooooowwww, behaved like all other computers did, refreshing the screen all the time.

The ZX81 contained only four main chips : the ROM, Z80A CPU, 1K RAM and the Ferranti custom-made chip! It is as simple as that. The machine was assembled by Timex Corporation in their Scottish plant.

This computer was a very great success in Europe in the beginning of the 80's. It was very cheap and a lot of people who now are working on modern PCs or Macs, made their first move on a ZX 81 even though its performance was actually poor!

A very great range of peripherals were developed for this computer, among them : 3.5" floppy disk units, keyboards, high resolution graphic cards, RS232 or Centronics interfaces, RAM expansions, etc... In fact, it was possible to make a pretty good computer from the ZX 81!

The range of expansion options was quite extraordinary. For instance, Memotech created a whole range of modules which would piggy-back, one after another (and using velcro pads to secure to each other and the to the ZX81, as there was no mechanical locking on the edge connector).

So, for instance, you could have additional memory (up to 128k!), high-resolution graphics, disc controllers, joystick controllers, serial ports, and so on.

Popular add-ons also included replacement keyboards - one was a series of mechanical keys which stuck over the membrane keyboard, others involved re-housing the ZX81 inside a new, larger case with a "proper" keyboard.

In fact, the options were - seemingly - endless. Sadly the power supply wasn't particularly stable, so "glitches" were common, resulting in a system reset and the loss of hours of painstaking coding!

It was followed by the ZX-Spectrum and was also sold as the Timex Sinclair 1000 in the USA.

Contributors: Silas Denyer

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This was my very first personal computer. I still remember when my father brought this home, I was about three!!!

Most people don't seem to keep powerful memories this early in life but I guess I do.

This thing was truly archaic but sleek and tiny at the same time. It used cassette tapes like many systems of it's day. It hooked up to the black and white Candle television, the first TV my family ever had.

Wrath of Khan is another first memory that stuck pretty vivdly with the bugs... the bugs!

Anyway, I digress...

I remember my father making some kind of alternate connection for the video.

Only a year or two after buying this system my father found something better for his job, which required better graphing capabilities and printing. He eventually bought a COCO 2, the Disk Drive and DMP-100 dot matrix printer.

The Sinclair became a toy for us, although I was fascinated by the colours of the new computer and quickly ditched this little thing.

The most I ever did on it was create simple text-based BASIC programs once I was a little older.

Tuesday 16th January 2007
Ean Bowman (Earth)

What I think has been lost in hindsight, is that the ZX81 at the time was a powerful calculator at a very friendly price. To think of ZX81 in relation to games I think is missing the point. At the price 1K was a lot compared to contemporary calculators, and a user was not locked to a tiny calculator display, but could draw full graphs on a TV screen

Wednesday 8th September 2021
Numanoid (Norway)

I bought this mail order as a kit and built it as a teenager in 1983. You had to solder the parts onto the board. Seeing it work after the painstaking assembly process was pure joy. I will never forgot that. I learned Z80 assembly on this which was like magic after doing a lot of 6502 on the Apple II. It also had a nice BASIC interpreter and the graphics mode was fun.

Monday 1st August 2016
Timothy Heider (Portland Oregon USA)


TYPE  Home Computer
ORIGIN  United Kingdom
YEAR  march 1981
KEYBOARD  Touch-sensitive keyboard, 40 keys
CPU  Zilog Z80A
SPEED  3.5 MHz
RAM  1 KB (901 bytes available, up to 64 KB)
TEXT MODES  32 x 24 (but 2 lines are reserved for system messages and commands)
COLORS  Black and white
SIZE / WEIGHT  167 x 175 x 40 mm / 350gr
I/O PORTS  Z80 Bus, tape, video
POWER SUPPLY  9V DC , 600 mA (centre polarity = +ve)
PRICE  Kit :£50 (UK, june 1981) / Ready-built : £70 (UK, june 1981)

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