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This page has a note about a chip called AMI SAGA. Apparently it does the same job as the Ferranti ULA, but saves a little circuitry and runs cooler.

What was this chip? Some kind of uncommitted logic array? Why would it run cooler, and save the chroma circuitry, and then why wasn't it also used in more ZX Spectrums?

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    "AMI" is most likely AMI Semiconductor and a SAGA is almost certainly some kind of Gate Array. No idea what the "SA" might stand for... – Brian H Jun 6 '18 at 17:40
  • Here's a page with pics of the board/chip in question markfixesstuff.co.uk/sinclair-spectrum/… – Alex Hajnal Jun 6 '18 at 19:10
  • @BrianH Sinclair/Spectrum Analogue/Advanced/Ablative Gate Array? – Alex Hajnal Jun 7 '18 at 3:59
  • My only suspicion as to why it wasn't used is that running cooler is of little benefit - cooling wasn't a huge issue (other than for the power supply circuit, but that was probably unaffected), and the chroma bias circuit is very cheap (just a handful of resisters and capacitors, I believe), so it may well be that if Ferranti discovered Sinclair were considering switching to another supplier they offered enough a reduction that switching wasn't worth the effort. – Jules Jun 7 '18 at 11:42
  • As to the name "SAGA", looking through a few data books it seems that in the early 80s all of AMI's chips had "S" as a prefix letter. As @BrianH suggests "GA" is almost certainly gate array. Not sure about the other "A" though. – Jules Jun 7 '18 at 11:45
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There doesn't seem to be an awful lot of information available about the AMI SAGA. What we do know is this:

  • It was designed as a replacement for the traditional Ferranti ULA that most Spectrums were based on
  • It was produced by American Microsystems, Inc, who specialized in CMOS gate arrays, and is therefore presumably CMOS rather than the current-mode logic (!) design of the Ferranti ULA. Current-mode logic is renowned for being fast but using a lot of power (its close relative, ECL, was used in the Cray-2 supercomputer, which used 150kW of power and had to be kept immersed in fluorinert for cooling), while CMOS logic is known for its low power consumption, which is probably why the AMI gate array runs cooler.
  • The design was abandoned due to a timing issue with the DRAM interface.
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    I like your comparing the ZX Spectrum to a Cray-1 ;) – tofro Jun 7 '18 at 16:42
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    @tofro I agree and endorse the comparison strongly: one's a supercomputer, the other's a super computer. – Tommy Jun 7 '18 at 16:47
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    Cray-1 was air-cooled, as were its descendants like the X-MP and so on. Cray-2 was fluorinert, as were the failed follow-on Cray-3 and -4 – Maury Markowitz Jun 8 '18 at 11:41
  • @MauryMarkowitz -- ah, yeah... does look like I got them mixed up. :) – Jules Jun 8 '18 at 16:23

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