If you have a SCSI interface, don't worry. You can overclock your 68k and let your SCSI
chip (now overclocked too ;-) live with it. In fact all the stories about "with the scsi you can't" are false two times:
the first, because it CAN be done :-) The second because it doesn't just work, it works better.
In fact overclocking the bus you can make your SCSI chain much faster. The crystal that gives the speed for the 68k
processor also affects the SCSI Chip. Just to do some examples, here with my 040
clocked at 33Mhz, with 66Mhz bus, the SCSI-II hard disk jumped from 5mb/sec to peaks of 8mb/sec! This in
synchronous mode, measured with SCSIBench (from Aminet). The 12x Pioneer CD-Rom, now transfers data at 16x, and so on!
The boot time, after the overclock, has reduced by 1/3, and the feeling is of a really faster and immediate system.
A reason more to overclock!
Notes on the chipset: My BlizzardPPC is equipped with a Symbios Logic marked chip for the SCSI, while other boards,
like the one in the photo, are equipped with a "Tolerant" marked one. I think they are almost the same, this Tolerant
should be a Symbios compatible chip. But I can't be sure that Tolerant chips are overclockable, but I think so.
Notes on the settings: I have experienced that some SCSI peripherals need a special setup to work reliably under an
overclocked controller. In some cases you may need to usa a lower Mhz setting from the BlizzardPPC bootmenu. In
other, you may need to disable the synchronous mode. The devices tested are:
Pioneer 12x CD-Rom
This drive works with 10Mhz synchronous mode, but under cd-burning sessions, it seemed more stable lowering the mhz, but may
be because the firmware of this drive is defective "by default".
A note: after overclocking it jumped to 16x transfers!
Epson GT-7000 Photo scanner
This scanner works perfectly with all the best settings activated. Also the film scanner works with no problem.
A note: the scanner works greatly also under Mac emulation, but only if the film adapter is plugged in, otherwise
you will see the SCSI error requester (happens also without overclocking).
Yamaha 4416S CD-Burner
The burner seems to have no side effects, no best performances, but also no problems at all.
With SCSI you can burn CDs when doing lots of other things, but after overclocking the CPU load is much lower,
allowing you to do many things more with no risk to get a buffer underrun. The lower CPU may depend not only from
the CPU overclock, but also for the overclock of the SCSI chip. Also, no problems when mastering on-the-fly from
an IDE HD hooked to the internal ide port.
Quantum Fireball SCSI-II 2,1gb HD (5400RPM)
The hard disk supports the sync mode and the reselection also after the overclock, and gave the best performance
improvement. Using SCSI Bench, the HD that before the overclock had 5mb/sec peaks, now reaches 8mb/sec. Cool!
UW Seagate Medalist Pro
This UltraWide scsi3 hard disk, hooked to the scsi chain with a 68>50 adapter, that gave, in sync mode, 6.5mb/sec with
the 50Mhz crystal. After the overclock, the hard disk refused to work with the sync mode activated. In async mode,
it still did 7,5mb/sec. I don't know if it happens due to the adapter, or due to a bad scsi implementation of the drive.
If you have more peripherals to report, mail them to me!
Notes on the chipset: My BlizzardPPC is equipped with a Symbios Logic marked chip for the SCSI, while other boards,
like the one in the photo, are equipped with a "Tolerant" marked one. I think they are almost the same, this Tolerant
should be a Symbios compatible chip. But I can't be sure that Tolerant chips are overclockable, but I think so.