Talk:Rigel (microprocessor)

Mariah & REX520 clock speeds

Mariah

I've changed the Mariah's speed range to start at 55 MHz rather than 62, the latter of which seems to be the clock used in the Vax 6000/5X0; this is based on the VaxStation 4000/60's cycle time of 18ns, but having just modified the page I've noticed that the MicroVax 3100/80 is listed as 20ns (50 MHz) and figured I should probably stop changing stuff, not least as there's always a risk that I'm failing to understand something! So I figured I'd leave this where people more knowledgeable than I am can comment...

--Vometia (talk) 11:31, 15 March 2021 (UTC)

As an addendum, just in case anyone knows, why are there so many formats for Vax model numbering? I've seen things like Vax 6320 but also Vax 6000 Model 300, VaxStation 3100/48 and also VaxStation 3100 Model 76 (and 3100 M76 and 3100/m76 but not 3100/76) but not 3148 nor 3176; and Vax 8650 and Vax 8800 but not Vax 8000 Model... argh. It was even more confusing when I worked at DEC, I couldn't keep up with the multiple names for things and lack of consistency!

And yeah, I know my capitalisation is wrong but I never liked ALLCAPS VAX. Plus "Virtual Address Extension Virtual Memory System" always seemed like a bit of a tautology.

er... etc. --Vometia (talk) 06:01, 18 March 2021 (UTC)

REX520

I guess this is also worth mentioning, which is that, according to the KA670 CPU Module Technical Manual (EK-KA670-TM-001), the Vax 4000/300's KA670 CPU module features a REX520 (DC520) Vax microprocessor clocked at 143 Mhz (28ns "microcyle" - their spelling...). The reason I'm not just editing the article to include this factlet is that I'm evidently being a bit hard of thinking or I at least need to read it (a lot) more thoroughly, because unless I'm doing it wrong, 28ns seems to come out as 35.7 MHz, which is exactly a quarter of the stated figure. 35 MHz seems a bit slow for a mid-range Vax 4000 and 143 MHz seems too fast, so I dunno what to make of it really. Anyone?

--Vometia (talk) 12:36, 17 March 2021 (UTC)

To answer myself, it seems this article answers my question: it uses a 143 MHz clock but the CPU speed is effectively (or actually, depending on one's PoV, or knowing what they're talking about; which I evidently don't!) 35.7 MHz because, er... something to do with "required a four-phase overlapping clock".

If I understand correctly, that means that it's "optimistic" (i.e. misleading) to refer to it as a 143 MHz CPU.

--Vometia (talk) 09:01, 18 March 2021 (UTC)