Editing Macintosh File System (section)

{{short description|Disk file system by Apple Computer}}
{{About|the MFS file system|other Macintosh file systems|Macintosh file system (disambiguation)}}
{{No footnotes|date=September 2013}}
{{Infobox filesystem
| name = MFS
| developer = Apple Computer, Inc.
| full_name = Macintosh File System
| introduction_date = {{Start date and age|1984|01|24}}
| introduction_os = [[System 1|System&nbsp;1]]
| succeeded_by = [[Hierarchical File System (Apple)|HFS]]
| partition_id = <code>Apple_MFS</code> ([[Apple Partition Map]])
| directory_struct = [[Table (information)|Table]]
| file_struct = [[Linked list]]
| bad_blocks_struct = No
| max_file_size = 20 [[mebibyte|MiB]]
| max_files_no = 4094
| max_filename_size = 255 characters
| max_volume_size = 20 [[mebibyte|MiB]]
| dates_recorded = Creation, modification
| filename_character_set = Any printable character except “{{mono|:}}”
| date_range = {{date|1904-01-01|MDY}} – {{date|2040-02-06|MDY}}
| date_resolution = 1s
| forks_streams = Only 2 ([[Data fork|data]] and [[Resource fork|resource]])
| attributes = version, locked, type, creator, Finder window, location in Finder window, Finder flags
| file_system_permissions = No
| compression = No
| encryption = No
| OS = [[System 1]] — [[Classic Mac OS#Mac_OS_7.6|Mac OS 7.6]],<br/>Mac OS 7.6.1 (read-only)
}}

'''Macintosh File System''' ('''MFS''') is a [[volume (computing)|volume]] format (or disk [[file system]]) created by [[Apple Computer]] for storing [[Computer file|files]] on 400K [[floppy disk]]s. MFS was introduced with the original [[Macintosh 128K|Apple Macintosh]] computer in January 1984. 

MFS is notable both for introducing [[resource fork]]s to allow storage of structured data, and for storing [[Metadata (computing)|metadata]] needed to support the [[graphical user interface]] of the [[classic Mac OS]]. MFS allows file names to be up to 255 [[character (computing)|character]]s in length,<ref>{{Cite magazine |last=Langowski |first=Jörg |date=April 1985 |title=Disks |url=http://mactech.com/articles/mactech/Vol.01/01.05/Disks/ |magazine=[[MacTech]] |volume=1 |issue=5 |archive-url=https://web.archive.org/web/20070927021320/http://mactech.com/articles/mactech/Vol.01/01.05/Disks/ |archive-date=2007-09-27 |access-date=2023-03-23 |url-status=dead}}</ref> although [[Macintosh Finder|Finder]] does not allow users to create names longer than 63 characters (31 characters in later versions). MFS is called a [[File system#Flat file systems|flat file system]] because it does not support a hierarchy of [[Directory (file systems)|directories]].

Folders exist as a concept on the original MFS-based Macintosh, but work completely differently from the way they do on modern systems. They are visible in [[Finder (software)|Finder]] windows, but not in the open and save [[dialog box]]es.<ref>{{Cite magazine |last=Brecher |first=Steve |title=HFS File Structure Explained |url=http://www.mactech.com/articles/mactech/Vol.01/01.12/HFSFileStructure/index.html |magazine=[[MacTech]] |volume=1 |issue=12 |archive-url=https://web.archive.org/web/20080426003220/http://www.mactech.com/articles/mactech/Vol.01/01.12/HFSFileStructure/index.html |archive-date=2008-04-26 |access-date=2023-03-23 |url-status=dead}}</ref> There is always one empty folder on the volume, and if it is altered in any way (such as by adding or renaming files), a new Empty Folder appears, thus providing a way to create new folders. MFS stores all of the file and directory listing information in a single file. The Finder creates the illusion of folders, by storing all files as pairs of directory handles and file handles. To display the contents of a particular folder, MFS scans the directory for all files in that handle. There is no need to find a separate file containing the directory listing.

The Macintosh File System does not support volumes over 20 MB in size, or about 1,400 files.{{Citation needed|date=March 2023|reason=Page 121 of Inside Macintosh Volume II (from the Bibliography section) describes the volume information structure, and while it doesn't explicitly state limits, the use of a four-byte integer for allocation block size and the use of a four-byte integer for end-of-fork locations two pages later implies that volumes up to 2 GB or 4 GB are representable.}} While this is small by today's standards, at the time it seemed very expansive when compared to the [[Macintosh]]'s 400 KB floppy drive.

Apple introduced [[Hierarchical File System (Apple)|Hierarchical File System]] as a replacement for MFS in September 1985. In [[System 7 (Macintosh)|Mac OS 7.6.1]], Apple removed support for writing to MFS volumes “as such writes often resulted in errors or system hangs”,<ref>{{Cite web|url=https://developer.apple.com/technotes/tn/tn1096.html |title=Technote 1096: Mac OS 7.6.1 |publisher=[[Apple Inc.]] |access-date=2013-09-16 |archive-url=https://web.archive.org/web/19990429061118/https://developer.apple.com/technotes/tn/tn1096.html |archive-date=1999-04-29 }}</ref> and in [[Mac OS 8.0]] support for MFS volumes was removed altogether. Although [[macOS]] (formerly Mac OS X) has no built-in support for MFS, an example VFS plug-in from Apple called MFSLives provides read-only access to MFS volumes.<ref>{{Cite web |date=2006-11-09 |title=MFSLives |url=https://developer.apple.com/library/archive/samplecode/MFSLives/Introduction/Intro.html |access-date=2023-03-13 |website=Apple Developer Documentation Archive}}</ref>