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projectgus @projectgus

Any vintage Apple buffs that can explain the ARM logo on this Macintosh Processor Upgrade Card (PowerPC 601 PowerMac, circa 1994)? I know Apple & VLSI were seed investors in ARM. Do old PowerPC chipsets have an embedded management core?

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@projectgus That looks like a NuBus card - possibly an upgrade card for an older 68k Mac? Then it's probably more something like some custom glue logic thing, and not a CPU in whichever form.

@galaxis it is indeed for upgrading a 68k Mac to a PowerPC. You're probably right, I'm just wondering why it has an ARM logo on it.

An earlier prototype has much the same chips, but no big ARM logo.

I think VLSI were the first ARM licensee - there could be an ARM in there, and given the label, I think there must be. Perhaps needed to setup the board for the PPC to boot.

@galaxis @projectgus

@EdS @galaxis Nice find!

Doing some kind of early boot configuration sounds plausible to me.

@projectgus @EdS According to it was possible to switch between the PPC and the m68k CPU with a reboot, so there must have been some pre-boot toggle to decide which CPU to power up - can't have been both on the bus.
The MacWorld image designates the chip as "040 bus adapter and cache controller", which sounds plausible (the card seems to have brought a Mac PPC ROM, but had to talk to memory and periphereals over the 68040 CPU bus).

@galaxis @EdS Good thinking.

My understanding is you could run a software tool in Mac OS to change it, which I'm guessing flips a bit in some non-volatile storage somewhere. I noticed the ROM stage of the Mac double-reboots (two chimes) the first time after installing or removing the card...

@galaxis @EdS I do, although I was found this cleaning it up to sell it as I couldn't think for a use for it...

It is tempting (albeit super fiddly) to change plans and try to poke around inside of it instead, though...

From Twitter comes a few clues:

Apple not the designer for these, Daystar.

A "real" PowerMac 6100 of the same era has no VLSI chips at all.

Similar era 68K Macs have lots of VLSI chips but nothing marked ARM.

@projectgus a quick bit of googling on the Apple part (820-0547-a) dusted off a few memories. So, these cards are funny and for the PDS slot. I'm going to go down the rabbit hole and read more about that stuff myself now and would suggest you do the same. But my gut feel is that the ARM chip isn't so much a Management Core as we think of them today as "Black magic to let you have a different CPU in the particular machine in question".

@trini It is indeed one of those cards.

Random glue logic makes sense. I would love to know why it's ARM's random glue logic, though...

@trini That's a VLSI chip. Custom memory controller or something of the sort? VLSI was one of the founding investors in ARM in 1990.