How Big a Hard Drive Does My Mac Support?

A Low End Mac reader with a Umax SuperMac S900 asked me, "What is the max size HD I can put in my machine?"

Back in those days, Apple still used SCSI drives on its Power Macs - as did the clone makers.

SCSI devices are somewhat intelligent, unlike IDE/ATA/SATA drives which are under control of the operating system and hardware interface. To the best of my knowledge, there is no maximum size for SCSI drives. Mac OS 7.5.1 and earlier cannot handle partition sizes over 2 GB, and from 7.5.2 through 8.0, the maximum is 4 GB. On top of that, you can have up to 8 (or was it 9) partitions per drive. With the introduction of HFS+ in Mac OS 8.1, that jumped to 2 TB.



If you're using more modern hardware with IDE/Ultra ATA hard drives, be sure to read How Big a Hard Drive Can I Put in My iMac, eMac, or Power Mac?, which explains the 128 GB limitation of the IDE bus in G3 and some G4 Macs.

 

G5 CPU upgrades?

I received an email wondering whether it's possible to upgrade the CPU in a Power Mac G5. It seems someone had a 2.5 GHz dual-core G5 module for sale on eBay....

The G5 Power Macs were all designed so that the memory bus ran at one-third (in some low-end models) or one-half of CPU speed, and the last generation dual-core Power Macs had a different architecture than previous G5 Power Macs. My guess is that while it may be possible to swap this CPU into a slower (2.0 or 2.3 GHz) Power Mac G5, the memory bus would not run any faster. Assuming the 2.5 GHz CPUs were running at full speed, this bottleneck would make the upgraded machine slower than a true 2.5 GHz dual-core Power Mac G5.

Then there's the question of whether it would run at 2.5 GHz. My gut feeling is that it would run at the same clock speed as the CPU that the Power Mac was designed for, although I have no hardware knowledge to back that up. While a 2.0 GHz or 2.3 GHz Power Mac G5 would benefit from twin dual-core CPUs, I suspect that would be the only benefit of such a transplant.

If you know more about G5 hardware, please tell me more.