Altair 8800 name Was: Re: Altair 680 Expansion Boards?

Eric Smith spacewar at
Sat Dec 24 16:39:46 CST 2016

On Sat, Dec 24, 2016 at 8:10 AM, Peter Corlett <abuse at> wrote:

> On Fri, Dec 23, 2016 at 04:14:28AM -0700, Eric Smith wrote:
> > The same trick works perfectly well with a 6502, and in fact was
> invented by
> > Don Lancaster using a 6502 years before the ZX80 was designed. That
> doesn't
> > really explain the choice of the Z80.
> Interesting. I was of the understanding that the Z80 video hack didn't
> work on
> the 6502 due to the latter being slightly pipelined and so the instruction
> fetch cycle couldn't be abused in the same way. Perhaps Sinclair couldn't
> get
> it to work on some dodgy 6502s that fell off the back of a lorry.

The details aren't identical, but on the 6502 it's abusing the fetch of
both an opcode and an immediate operand.

If there was nothing in it, then it's a mystery why the Z80 was selected.
> However, Sinclair wasn't exactly one for making rational design decisions
> based
> on technical merit or industry best practice.

As much as I like the 6502, the Z80 is better in some ways, particularly if
you want to do a lot of 16-bit add and subtract.

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