G3 Chip Compatibility

[eraser]

Does anyone happen to know if the entire range of G3 CPUs are pin-compatible with one another? In other words, can a 750FX (Sahara G3) be soldered onto a CPU card in place of an original G3 (Arthur)?  I know that the G4s are surprisingly interchangeable and I am hoping that the G3s are as well.

 

[trag]

There have been a number of discussions, in detail, on this very point.

Basically, the early PPC750's which have pins to support external L2 cache are all pin compatible.  They may require different voltages, or configurations on some signal pins (PLL configuration pins, e.g.) but the balls are in teh same place.

The PPC740 is different, because it does not have the capability of supporting an L2 cache, so those pins are not present and all the pins are rearranged.

The 750CX adds a 256K on-board L2 cache, and so again, the external connections to control the L2 cache are omitted so the pinout changes.   However, the 750CX is also not compatible with the 740 pin arrangement, although it seems like it could have been.   Perhaps they're in different size packages, I don't remember.   They are enough years apart, the process technology for the die could have changed and so the package size may be different as well.

The 750FX and 750GX are compatible with each other, but are a  change from the 750CX for some reason.

So, for example, if you have a PPC750 with external L2 cache support and want to replace it with a later model that moved the L2 cache on chip, it will not be an easy task because the pin/ball arrangement changed.

 

[eraser]

Thanks trag!

The interesting thing about the G4s was that if a new G4 with L2 cache was attached to a new CPU board it would treat the former L2 as L3 cache.  I was hoping that was the case with the G3s.

 

[Franklinstein]

Yeah it's kind of a tricky subject, at least as far as use in Macs goes: sometimes they may be pin and signal compatible but ROMs don't recognize the new chips so they won't work. Upgrade suppliers such as Sonnet, Newer, and Daystar had custom firmware updates for some models that used new chips, such as the 7448 upgrades for late-model PowerBook G4s and G4 upgrades for B&W G3s (though these models supposedly worked with G4s until Apple blocked them with an "update", thus requiring a 3rd party firmware patch to reenable the use of a G4).

Chips that are supposedly pin-compatible:

QFP 240: PowerPC 603, 603e

CBGA 255: PowerPC 603e(v), 604(e)(v), 740

CBGA 360: PowerPC 750(L), 7400, 7410 

CBGA 292: PowerPC 750FX, GX

CBGA 483: PowerPC 7450, 7455, 7457

CBGA 360: PowerPC 7440, 7445, 7447(a)(b), 7448 [though it's still a CBGA 360, it's not compatible with the earlier CBGA 360 used by the 750/7400]

Maybe one or two of the PowerPC 970 variants are pin-compatible but they're epoxy-sealed to their carrier boards so they're very difficult to rework. Not that there would be much reason to do it anyway.

The PowerPC 750CX has a unique BGA. 

Though they use the same 304-pin QFP package, the PowerPC 601 is not pin-compatible with the 601v, nor with the QFP variant of the PowerPC 604. 

 

[trag]

Though they use the same 304-pin QFP package, the PowerPC 601 is not pin-compatible with the 601v, nor with the QFP variant of the PowerPC 604. 

Are the pinouts different between the 601 and the 601v or is it just that the 601v expects 3.3v where the original 601 used 5V on the power pins?  Oh, and I/O as well.   3.3v vs. 5V.     Interesting to look at the Power Computing Power120 PPC601 surrounded by level shifters.  At least I think I remember correctly that those are level shifters.   It's actually been a decade or more since I looked at it...

Excellent table of chip packages and compatibilites.   Very nice.

 

[Franklinstein]

the 601v expects 3.3v where the original 601 used 5V on the power pins?  Oh, and I/O as well.   3.3v vs. 5V. 

Yep. Exactly this. It's unfortunate because, as I had posted in another thread, I had hoped to replace a 60 or 66MHz 601 with a >100MHz 601v or 604 but it's not possible because of the voltage differences to the 601v and the reassigned pins on the 604. A 6100 with a 120MHz 604 would be pretty cool but sadly is impossible.