why only 1k of ram?

[Crayon21]

even the Vic 20 had more. the about zx80/81 section calls it massive. what's so massive about 1024 kb? curious to know

[Lardo Boffin]

I suspect to keep costs down. The ZX81 was built to a cost more so than functionality level.

[1024MAK]

Sinclair’s aim with the ZX80, was to produce the lowest cost, but fully functional home computer that was possible. Hence every single part of the design and manufacturing was geared towards this.

Apart from the Z80, the ROM chip and the RAM chips, all the remaining chips were inexpensive standard 74LSxxx series parts.

The ZX81 was designed to lower the cost further. Hence the ULA replaced ALL the standard 74LSxxx series parts. A keyboard made of a plastic membrane also lowered the cost.

This left the ZX81 with a smaller (and cheaper) PCB, with only four chips or only five chips. The chips are:

• Z80A or more likely a NEC unlicensed clone (NEC D780C-1) CPU
• ULA
• Mask ROM
• 1K byte SRAM chip

or

• Two 1K by 4 bit SRAM chips (combined giving 1K byte)

So why 1K? Because this was the most cost effective SRAM chip available at the time that provided the minimum functionality that suited Sinclair’s requirements.

At that time, all RAM was very expensive. SRAM was very simple to use, and did not need any support chips. Whereas DRAM chips for larger amounts of RAM were cheaper per byte, but needed support chips. Complexity that Sinclair did not want.

To see an indication of how much DRAM cost, look through adverts in the magazines of the time and compare the cost of a ZX81 and that of a 16K RAM pack for it.

Mark

[Rich Moore]

The limitations of the machine, particularly the 1k ram, is part of the charm of the zx81. It forces better, at least more efficient, programming. Quite clever to sell the ram expansion as an 'optional' (!) extra. When they released the zx80 and 81 what was their market? There were plenty of utility programs and I remember most ads were aimed at serious, grown up markets ie for office use. The home gaming market hadn't really been invented yet and I wonder if the birth of this market was partly a happy accident. Was it initially developed by Sinclair as just a very programmable calculator?

[David G]

even the Vic 20 had more

When the VIC-20 came out it only had 5K RAM and cost $299. The ZX81 had 1K and only cost $149 USD -- 1/2 the price. And prices dropped fast. I bought my USA version ZX81 for $99 -- which was before the Timex/Sinclair debuted (which had 2K)

the about zx80/81 section calls it massive. what's so massive about 1024 kb? curious to know

There were home computers sold before the ZX81 with less RAM than 1K although perhaps the most notorious example being the Texas Instruments TI-99/4A which only had 256 bytes and came out after the ZX80

The home gaming market hadn't really been invented yet and I wonder if the birth of this market was partly a happy accident. Was it initially developed by Sinclair as just a very programmable calculator?

The ZX81 was the evolution of the Sinclair ZX80, which was designed specifically to be a home computer. The home gaming market was defined -- at least in the US -- by the Atari 2600 which came out three years earlier

home computer was rapidly evolving in the early 1980s, so keep in mind that when the ZX81 appeared, it was not judged the same as two years later ... it was stupendously great at first in the sense that it was the best you could buy under $149. But by 1983 was already old tech ...

[marste]

The limitations of the machine, particularly the 1k ram, is part of the charm of the zx81. It forces better, at least more efficient, programming.

Completely agree, and it's like this even in 2021 !!!

For this reason I particularly like the ZX81, else I would go for modern computers that have better ... everything!

[dr beep]

The limitations of the machine, particularly the 1k ram, is part of the charm of the zx81. It forces better, at least more efficient, programming.

Completely agree, and it's like this even in 2021 !!!

For this reason I particularly like the ZX81, else I would go for modern computers that have better ... everything!

The 1K limitation is not a limitation of the imagination. Without this limitation I would never have coded 1K hires games.
My first hires game was 16K, a version of my ZX Spectrum game on the ZX81, but I found the 1K hires demo from Wilf Righter and thought
"How can I make a game out of a demo?". The result now: 74 1K hires games, sometimes defying the 1K limits.

[dr beep]

BTW, I have an idea for a game, easily to code in 16K, but I want to try a 1K version.

[marste]

Yes, every modern computer will become obsolete in very short time, while the 1K CHALLENGE will be forever!