Paralel said:

Here are the official SCSI transfer rates for given Mac models according to Apple:

http://support.apple.com/kb/TA29470?viewlocale=en_US

Most of them really suck, of course, since many of them are based on the 53C80, this is no surprise.

Also, for the PB 500 series, when it says "Custom IC" they really mean it's a 85C80 derivative smashed together with the serial controller into one chip, probably to save space/money/etc...

Click to expand...

Interestingly, the tech note doesn't mention the second Fast Internal Bus in the 8100.  Only the external/internal bus is mentioned.  The "custom" chip starting with the AV Quadras and running through the NuBus PowerMacs and on into the PCI PowerMacs is the AMD AM79C950 which Apple called CURIO.  It containsthe equivalent of a 53C94, an 85C30 and some kind of ethernet MAC.  It was a custom job from AMD for Apple and the datasheet is not available.

The 8100 was the first Mac with a Fast SCSI bus in addition to the regular slow bus.  While the Q900/950 had dual SCSI busses, they were both based on the 53c96.   The 8100 used the  53CF96 for it's internal Fast bus.

After the 8100, Apple switched to their "MESH" chip for the internal Fast SCSI busses in the PCI PowerMacs.  I suspect, but don't know, that MESH is really just a licensed 53CF96.   One of these days, maybe I'll try replacing one with the other to prove or disprove it.