43

The ZX80 and ZX81 use the Z80’s opcode fetch bus cycle for graphics collection — the opcode fetch is appropriated to obtain a character index and the refresh cycle is used to obtain a row of pixels. Of course the actual refresh address isn’t actually likely to be correct for the pixel fetch so the ULA replaces the low nine bits with a combination of the ...


18

Sinclair's use was a very unique case in a very specific situation that never occurred again later on. Production side: There were many more manufacturers of chips back then. The ones that wanted to compete at the forefront used RAMs as gateways to technological development. (*1) Anyone not ramping up their output fast into the upper 90s will lose money. ...


9

##TL;DR: Not really sure where this claim of over 5 M computers, including 1 M Spectrum comes from. While still not correct, it would sound more believable the other way around, as 5 M units, including 4 M of Spectrums. So my guess is, that it's for one a very rough number, but more important the author simply used the wrong label for the additior. Deails: ...


9

Directly to answer your question: yes, if the RAM copy is substituted after the machine has started up; otherwise, not reliably, as it's likely the first five bytes have been altered. With reference to The complete Timex TS1000/Sinclair ZX81 ROM disassembly notice the 'skip constants' routine starting at the bottom of page 87 of the PDF, page 52 of the ...


7

Answer: no it can't. This is a later model Executive with the H/L switch (serial number 131131); apparently my manual and calculator don't match! Anyway, the calculator goes into a loop. It doesn't "break" in that it can be cleared (or switched off, or the batteries removed) but it certainly tries to calculate the answer without detecting an ...


7

The Memotech MTX (1984-5 or so) has a wire link on its circuit board that allows you to use half-good chips. I dont think I’ve seen any being used, but it seems the designer thought it at least possible they might want to.


4

tl;dr: I suspect the introduction of heavily subsisdied Japanese memory fabs was a key factor; once they started to flood the market with their RAM, it simply wasn't worth the extra risk/hassle of buying "half-bad" RAM chips when Japan was dumping out perfectly functional RAM at below cost. https://apnews.com/article/...


3

A slightly different situation, but you can buy a brand new MacBook Air right now where only seven out of eight GPUs are working, and save $50. And all new Macs with an M1 processor are sold with either 16GB or 8 GB of RAM, they are obviously tested and there is no reason why a failing 16GB CPU wouldn’t be sold as a working 8GB CPU. So it seems that Apple ...


1

I am adding second pic. Looks like I can't post more than one.


1

Here comes serial from mine z88. Was bought in Croatia and during retro meetings it came to Novi Sad, Serbia. Added two pic because one is not so clear. [


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