Talk:Macintosh File System

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The articles states that MFS only supports 20Mb disks, however the specification allows up to 256Mb. It also says it has a value in an Apple Partition Map, and I'm not so sure about it. Anyone checked? —Claunia 18:56, 13 March 2006 (UTC)

According to [1], for the Partition Map Entry Record the pmParType field (which contains a string that identifies the partition type) can contain the string Apple_MFS which means "Partition uses the original Macintosh File System (64K ROM version)." I cannot find info on the maximum MFS volume size (either theoretical or in practice). 22:28, 2 May 2006 (UTC)
MFS gives a disk a maximum of 4096 allocation blocks, and uses a 32-bit integer to store the size of each block. So theoretically, the maximum disk size should be 65535 * 4096 bytes, which is approximately 256 MiB (although in this case, the minimum size of each file would be 64 KiB!).
However, when I try formatting a 300 MiB disk image under System 1.1 or System 2.0 in Mini vMac, I end up with a partition that appears to be approximately 12368 KiB large. Whether this is a limitation of the Finder or something else, I'm not sure. — CharlesJS (talk) 06:52, 30 November 2009 (UTC)

Filename character limits[edit]

As far as I know, no Finder that supported writing to MFS (7.6 and before) supporting making filenames longer than 31 characters. Also, HFS+ (or Mac OS Extended) under the Finder in Mac OS X supports up to 255 characters. So, the claimed 63 character limit for the Finder (in general) is inaccurate. (I do not believe there ever was a 63 character limit Finder.)

Tested with Finder 1.0?
Please sign your comments.
Claunia 20:58, 1 May 2006 (UTC)
No. But I tested with Finder 1.1g. Seems I was wrong. There is also, if the Finder is to be believed, a 27 character limit imposed on application and disk names. 04:54, 2 May 2006 (UTC)
I don't think the Finder is to be believed xD. Just the Toolbox APIs and the File Manager, as documented in Inside Macintosh. E.g. in Mac OS 9 any app can use APIs to write filenames up to 255 chars in HFS+, but the Finder will still see only 31. About the volume name, it is smaller in both MFS and HFS than the filename limit but I don't remember the exact limit.
Claunia 09:04, 2 May 2006 (UTC)
Did some more experimenting. It seems (at least) as of System 3/Finder 5.1, the Finder implements its 31 character limit (it still says 27 for application and disk names) on both MFS and HFS disks. System 3/Finder 5.1 matches the System Folder that shipped with the Mac Plus when first shipped. 00:25, 3 May 2006 (UTC)

MFS read/write capabilities[edit]

The infobox says, "System 1 — System 7.5.5 (Write), System 8 (Read)" for supported operating systems. Yet the article says, "In Mac OS 7.6.1, Apple removed support for writing to MFS volumes, and in Mac OS 8 support for MFS volumes was removed altogether." Which is right? 01:39, 11 September 2006 (UTC)

Technically, both are correct. The article should probably read 7.6, rather than 7.6.1; but the MacOS development tree for Version 7 wasn't totally linear. See this for further information. (talk) 08:30, 19 July 2013 (UTC)


Yes, I know "MFS file system" is an example of RAS syndrome. I just thought the alternative would have been even sillier: "This article is about the file system called the Macintosh File System. For other Macintosh file systems..." Smiley.svg - (), 06:51, 31 January 2007 (UTC)