pci logic boards query

[beachycove]

Is there any difference between the logic boards of the 7500, 8500, 7300 and 7600? Or, indeed, were there revisions of the logic boards within the same series (e.g., the 8500) as the processor speed improved, etc.?

Presumably the (original, non-Kansas) 8600 is a different animal, as is the 9500 and the 7200, but what about the rest? Video system etc. etc. all identical or different?

I hear lots about the boards being interchangeable, but am not sure just how far that piece of wisdom really goes.

Here's another way of putting the question: if swapping logic boards between early pci macs, which is the best?

 

[Quadraman]

They all have different part numbers, but I personally see little or no difference between my 7500 and 7600 motherboards. I know that the 7300 is missing some circuitry to do with the A/V connectors that was present on the 7500 and 7600 which was the reason why the numerical designation went down instead of up.

 

[LSD]

I combined a 7300 and a 7600 into one machine a while back. It hasn't worked reliably since (it has a little trouble booting up. You'll hear the chime and then nothing) but I have no idea if that's the logic board or something else :/

 

[beachycove]

As to the non-working machine, it must be due to a logic board/ memory/ hd fault, as the psu etc is one and the same.

Anyway, that's one difference named that I didn't know about. Any others?

 

[trag]

The 7600 and 8600 use a different power supply from the 7500/8500, IIRC.

The 8500 and 8600 include a couple of extra chips for the video capture or maybe that was video export. The 7500 and 7600 do either import or export, I can't remember which. The 8500 and 8600 do both import and export.

The 7500 and 7600 motherboard have the positions on the circuit board for the extra chips which the 8500 and 8600 actually have on board, so they're the same raw boards, simply populated differently.

The 7300 and the 8600 have a slightly updated ROM, $77D.34F2 instead of $77D.28F2. The 7600 also has the 28f2 ROM. On the boards, the four 28F2 ROM chips are labeled 341S0169 through 341S0172. The 34F2 ROMs are labeled 341S0280 through 341S0283.

The 8600 enhanced and 9600 enhanced (Kansas/Mach V machines) have yet another ROM, the $77D.34F5, which is labeled 341S0380 through 341S0383.

The switch from 8500 and 9500 to 8600 and 9600 moved virtually the same motherboards (updated power connector and ROM) into a nicer case. The update to 8600 and 9600 Enhanced kept the nice case and added the later ROM and ability to use the Mach V CPU cards. Also, the 9600 Enhanced lacks the on-board L2 cache found on the 9500 and 9600 boards, but the positions for the chips are still there, but unpopulated.

The 7300 also did away with the video import/export ability altogether.

Jeff Walther

 

[LCGuy]

Also, don't the 7300 and 8600 use a different PSU to the 7600 and 8500?

 

[beachycove]

Thanks for this. Great information.

One more heave: Is the 9500 significantly different? I know that, like the 9600, there's no on-board video on the 9500, nor any on-board av capability; there are also 5 pci slots, rather than 3. Is that it? It was in its day a very expensive piece of hardware, but I suppose that could be just because it was such an early pci mac.

 

[Bunsen]

6 PCI slots

 

[LCGuy]

Yeah, there are 6 PCI slots, but one must be used for the video card, due to the aforementioned lack of BIV, so the available number of PCI slots will always be 5.

 

[beachycove]

6 pci slots it is, indeed. (I went and counted.)

And what else, if anything? Special I/O, scsi or the like? I see on my busted 9500 logic board that there are some chips that don't seem to be on the 7500 logic board that I have lying around.

 

[trag]

6 pci slots it is, indeed. (I went and counted.)
And what else, if anything? Special I/O, scsi or the like? I see on my busted 9500 logic board that there are some chips that don't seem to be on the 7500 logic board that I have lying around.

The 9500/9600 has six PCI slots and 512K of level 2 cache soldered to the board. They lack the level 2 cache slot found on the 7x00 and 8x00 machines and they lack the built-in video abilities. Other than that, they are identical. The I/O hardware is identical.

All of the I/O goes through the Grand Central chip which appears as a PCI device to the computer. So there are actually four PCI "slots" on the 7500/7600/8500/8600/7300 machines.

The PCI bus is controlled by the Bandit chip which bridges data from the CPU/memory bus to the PCI bus. The non-9500/9600 machines have one Bandit chip bridging for Grand Central and the three PCI slots. The 9500/9600 have two Bandit chips. The first one does exactly the same job as the single Bandit chip on the 7/85/600 machines. The second Bandit chip bridges for the additional 3 PCI slots.

So each Bandit chip occupies a spot on the CPU/Memory bus. In the non-9500/9600 machines, there is one Bandit chip, plus the video controllers, Control and CHAOS. The Control/CHAOS combo occupies the CPU/Memory bus space which the second Bandit occupies on the 9500/9600, sort of.

Apple originally designed this family of machines to be capable of having four Bandit-style bridges on the CPU/memory bus. So, in theory, they could have built a machine with 12 PCI slots, or one with 9 PCI slot plus built-in video.

Additionally, Bandit is capable of controlling more than three or four PCI devices. The Apple Network Server uses Bandit PCI Bridge chips. It has six PCI slots, one Grand Central, on-board PCI video, and two F&W SCSI busses on the PCI bus, for a total of ten PCI devices on two PCI bridges.

But wait, there's more. In the Apple Network Server, the video, two SCSI busses, Grand Central and first two PCI slots are all on one Bandit chip. So that's actually six PCI devices on one PCI bus.

So with four Bandits and six devices per Bandit, one could theoretically have 24 PCI devices. Unfortunately, problems with bus noise limit one to about 5 PCI slots per bus. One can have ten soldered down devices, because soldered down devices are less noisy and probably have less trace length than cards. So figure each slots counts twice and each soldered down device counts once, and you're limited to a count of eight to ten per Bandit chip.