How Large a Drive Does My Mac Support?

Originally published 19 February 2001 as a Mac Daniel column for Low End Mac.

Q: I have a Mac SE running System 6. What's the biggest hard disk I can use? I've heard some things about a limit of the hard disk size on an SE.

A: Just to dispel a bunch of nasty little rumours that seem to be floating around, there has never been an inherent hardware limit on hard disk size on any Macintosh. The limitation on hard disk size has always rested squarely in the operating system and the hard disk formatting.

Any Mac running System 6 has a two gigabyte limit on maximum volume (partition) size, but any hard disk can be used as long as the largest partition is under 2 GB. For example, you could use a 9.1 GB SCSI HD with any Mac no matter what the OS as long as the largest partition on it was under 2 GB. Also note that Apple's drive partitioning tools only support up to eight partitions per drive, so 16 GB is a realistic limit through System 7.1.x.

This limit was increased to 4 GB with System 7.5 and then to 2 terabytes (TB) with System 7.5.2 on some Macs (See Apple KBase Article 8647 for details), but your SE is not among them. Any Mac running OS 8.1 with HFS+ formated drives will also support 2-TB partitions, so if your Mac is running 8.1 or later, you can use any SCSI-based hard disk on the market today (with the appropriate adapters, if necessary) without partitioning.

Of course, this brings up two caveats: using partitions greater than 2 GB under HFS is incredibly inefficient due to the large block sizes required *, and running System 7.5 on a Plus, SE, or Classic is not a good way to "more efficiently" use a large hard disk. System 7.5 is far too slow to be used on the 68000-based Macs in daily use, and coupled with the efficiency factor I just mentioned, well, it's just not worth it.

*HFS Plus, which is a far more efficient method of formatting due to its smaller block sizes, is only available on Mac OS 8.1 and later, and 680x0-based Macs can't use an HFS Plus-formatted drive as a boot drive.

copyright ©2000-2004 by Chris Lawson