[G4] Note on ATA buses in MDD Dual G4 and perhaps other Macs.

[Aaron]

Every time I solve one problem with my new G4 Dual MDD,  I find new ones! It's sometimes very frustrating. But the following problem that I encountered and solved provides some useful info that many users of these machines may not be aware of.

After fixing my second optical drive so that the tray would come out the door*, and then putting everything back together and starting the computer, I pressed the Eject button and ... the NEW drive's tray opened. Option-Eject did nothing, and I couldn't open the stock SuperDrive's tray, although both drives were seen by System Profiler.

I soon realized that it might have something to do with the fact that I had connected the optical drives' ATA cable to the presently unoccupied ATA 66 bus, rather than the normal ATA 33 bus. Turned out that when I reconnected it to the latter, everything worked!

My guess is that the jumpers on the two drives were set using the Master/Slave method, which apparently is correct for the ATA 33 bus but not for the ATA 66 bus, which, like the ATA 100 bus, uses Cable Select!

Hope somebody finds this useful -- or can correct me if my interpretation is wrong!

 - Aaron

* See the thread, "[G4] Mirrored Drive Doors block tray on my second optical drive."