Sinclair ZX80 on Ebay

Phill Harvey-Smith afra at
Sat Oct 24 05:12:11 CDT 2009

Julian Skidmore wrote:
> Hi folks,
>> Well I was. Was the difference the fact video stopped when the cpu
>> was not in the idle key press loop?
> There's quite a few differences between the ZX80 & ZX81.
> The ZX81 supported 'compute and display' thanks to its more 'advanced' 
> video chip!

Though I believe that the hardware of the ZX80 can be modified to 
support this.

> The ZX81 was (AFAIK) the first use of a gate-array chip in a home computer!
> The ZX81 had an 8K ROM with floating point arithmetic, 'graphics';
> decent string-handling and ZX printer support!

The 8K rom was available as an upgrade for the ZX80, along with a new 
keyboard overlay. Also the ZX81 ROM will work if plugged into a ZX80, 
the converse is also true a ZX80 ROM will work in a ZX81.

> The ZX81 was unbelievably slow!

Well, the ZX81 has two modes, SLOW and FAST, in SLOW mode it maintains 
the display as well as running programs, in FAST mode it esentially does 
the same as the ZX80, it only maintains the display when idle, so runs 
much faster.

> The ZX80 had that certain 'je ne sais quoi' that makes it at least
> worth 10x more than any ZX81. I'm convinced about this, being the lucky
> owner of one* ;-)

Well they are cirtainly less common, and have the advantage of being all 
standard chips, which means if something breaks you can almost cirtainly 
repair it.

I think the main difference between the two machines is that the ZX81 
took all the LSTTL gates of the ZX80 and combined them into a ULA, which 
brought the chip count and therefore the cost of production down.



Phill Harvey-Smith, Programmer, Hardware hacker, and general eccentric !

"You can twist perceptions, but reality won't budge" -- Rush.

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