Just to add a bit more confusion ;-) On 20 Jun, this message from Michael Schmitz echoed through cyberspace: >> > Seems in this case it can't. My external disk only runs at 5 MB (of >> > course). >> >> External is different. Since Apple wisely decided on a 25-pin scsi >> cable scheme for external disks, they can only get up to 5MB/s >> there. [Sarcasm] So they used a separate controller for that. The > > Nope, not on a Powerbook at least.
Well, here are a few explanations as far as I know about SCSI on Macs: - external SCSI connectors have always been 25-pin Dsub connectors, except the Powerbooks with their square connector - maximum speed has always been 5 MB/s, conforming to either the SCSI-1 standard on very old hardware, or SCSI-2 (from some more advanced 68k designs onwards) - older designs _may_ not have been capable of synchronous operation (which provides speeds at or above 5 MB/s) - Macs always used either 5380 (very old 68ks), some variant of 53c9x (later 68k and external on some first- and second-generation PowerMacs), or MESH (late PCI-based designs) - the exception to the 5 MB/s rule are the second busses on some PCI PowerMacs (73/75/76/85/86/95/9600), which are internal-only, and implement Fast SCSI-2 (i.e. 10 MB/s) in a MESH design. Hence the label 'Fast' on the internal connector ;-) - all other MESH implementations are 5 MB/s only. Why not faster on the 25-pin connector? Well, every SCSI signal should have a seperate ground return pin (which means twisted-pair transmission lines end-to-end). That's not possible on the 25-pin designs, so signal quality is rather poor. Hence the speed limit... Now we only need to find out whether their choice of low-speed SCSI drives influenced the hardware designs, or the other way round ;-) Cheers Michel ------------------------------------------------------------------------- Michel Lanners | " Read Philosophy. Study Art. 23, Rue Paul Henkes | Ask Questions. Make Mistakes. L-1710 Luxembourg | email [EMAIL PROTECTED] | http://www.cpu.lu/~mlan | Learn Always. "
