Mac Plus: What is the maximum hard drive size supported?

The maximum volume size is 2 GB (4 GB with System 7.5.x). The hard disk must be HFS (Standard), not HFS+ (Extended). You may have to manually set an interleave ratio of 3:1 when formatting. A larger drive can be partitioned. See also KB article # 11333.

Jan

Tobias
The early external hard drives supplied by Apple for the 512Ke (serial, from the floppy disk drive's DB-19 port, or add-in Dove SCSI card) and Plus were 20MB (serial), and 20 and 40MB (SCSI). The 5.5-in SCSI drives had an interleave factor of 3, ie three platter revolutions were needed to read each track on a drive, a consequence of the slow data transfer rate (312 kB/s) through the SCSI port. The 20MB drives can, from time to time, still be found in original trim, but most of them were replaced with 1:1 interleave 3.5-in drives in the same enclosures when that became possible (from the time of the SE/Mac II onwards).

It was not until System 6.0.8 (or thereabouts) that Systems could cope with more than 32MB of drive storage.

Tobias,

I assume that you are referring to Apple HD SC Setup. Normally, the utility by itself will set a correct interleave. If one must format the hard disk at another Mac, it is possible to choose a ratio manually (to do this launch the Apple HD SC Setup application, and then press the two keys Command + I).

Apple HD SC Setup is intended for Apple drives, that have not been reformatted by a third-party program. Other drives will, typically, require a third-party utility.

It cannot be ruled out that more modern hard drives, due to some kind of data buffer, will work with a Macintosh Plus even if a 1:1 interleave ratio is chosen. However, 3:1 was the original value.

Jan

Tobias
Mea culpa. It was System 4.1 that introduced the ability to deal with more-than-32MB drives.