How Big a Drive Does Mac OS 9 Support?

Someone in our Facebook group asked an interesting question: “Anyone know the maximum size flash drive that can be used in OS 9.2 on a 300 MHz iBook G3?”

blueberry iBookI have to admit, he had me stumped. Someone quickly chimed in that Apple’s HFS+ supports up to 2 exabytes (an exabyte is a million terabytes, and the biggest drives at present are in the 8 TB range), but that didn’t seem realistic. So I did what anyone with an Internet connection would do, I asked Google how big a drive Mac OS 9 supports.

As expected, it was a whole lot less than 2 exabytes. But I got conflicting information from Apple. Mac OS 8, 9: Mac OS Extended Format – Volume and File Limits says it supports 2 TB volumes. Mac OS 9 Booting: Hard Disk Size Limit? puts the limit at “about 190 GB” and Macintosh: Using 128 GB or Larger ATA Hard Drives says for use with Mac OS 9.2.2, each partition must be no larger than 200 GB.

As covered in How Big a Hard Drive Can I Put in My PowerPC Mac?, most G4 Macs – especially those introduced before 2002 – do not support UltraATA* drives over 128 GB capacity, and with the G5, Apple moved to SATA drives, where that’s not an issue. This is a hardware issue, not an operating system issue or file system issue.

For G3 Macs, there is no native support for “big” (over 128 GB) IDE hard drives, so hitting the 190-200 GB ceiling isn’t even possible.

What About USB?

SCSI and FireWire don’t have maximum drive size restrictions, although hardware that bridges an IDE drive to FireWire may have such restrictions. For instance, most early FireWire enclosures for UltraATA drives do not support “big” drives.

As with SCSI and FireWire, USB drive capacity is limited only by the file system used, so any Mac running OS 9 should have no trouble using USB flash drives up to 200 GB capacity – and higher than that if the user wants to partition the drive. (Mac OS 9 allows up to 21 partitions, so in theory you could use a 4 TB drive.)

The only drawback flash drives have is the speed of USB, and older Macs such as the first two clamshell iBooks and tray-load iMacs only have USB 1.1 ports for expansion. That’s horribly slow by modern standards. It was slow compared to SCSI and IDE when that first USB-only iMac arrived in 1998. USB 2.0 is 40x as fast, FireWire is faster than that, and USB 3.1 is almost 100x as fast as USB 1.1.

So while you can have a 200 GB USB flash drive on one of those old Macs with USB 1.1, you are going to have to be patient. It will take a long time to write anywhere close to that much data to them, so maybe you’ll want to let it run overnight.

Still, you can do it. Any flash drive below 200 GB should be no problem at all with any Mac running OS 9. (Tthis should apply equally to Mac OS 8.1 and later as well. We will investigate further.)

Update: We’ve already heard from someone successfully using a 500 GB SATA drive with a SATA PCI card and running OS 9 with one partition. If you have results to share, please use the comments. Thanks!

* We use the labels IDE and UltraATA interchangeably.

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