Apple File System

The following information covers the file system used in Apple OS 9 and newer. A healthy understanding of the file system makes working with them a whole lot easier.

1. What was the Apple File System in OS 9? HFS Stands for "Hierarchical File System." HFS is the file system used for organizing files on a Macintosh hard disk. When a hard disk is formatted for a Macintosh computer, the hierarchical file system is used to create a directory that can expand as new files and folders are added to the disk. Since HFS is a Macintosh format, Windows computers cannot recognize HFS-formatted drives. Windows hard drives are typically formatted using WIN32 or NTFS file systems.Since HFS was not originally designed to handle large hard disks, such as the 100GB+ hard disks that are common today, Apple introduced a updated file system called HFS+, or HFS Extended, with the release of Mac OS 8.1. HFS+ allows for smaller clusters or block sizes, which reduces the minimum size each file must take up. This means disk space can be used much more efficiently on large hard disks. Mac OS X uses the HFS+ format by default and also supports journaling, which makes it easier to recover data in case of a hard drive crash.

2. What is the Apple File System in OS X? HFS+ The Mac OS Extended Format (HFS+) is a volume format compatible with Mac OS 8.1 and higher, including Mac OS X. In terms of volume, folder, and file size limits, it is similar to the Macintosh Standard Format (HFS).HFS+ or HFS Plus is a file system developed by Apple Computer Inc. to replace their Hierarchical File System (HFS) as the primary file system used in Macintosh computers (or other systems running Mac OS). It is also one of the formats used by the iPod music player. HFS+ is also referred to as Mac OS Extended Volume Hard Drive Format, where its predecessor, HFS, is also referred to as Mac OS Standard.

3. Why did the Apple File System change from OS 9 to OS X? HFS+ is an improved version of HFS, supporting much larger files (block addresses are 32-bit length instead of 16-bit) and using Unicode (instead of Mac OS Roman or any of several other character sets) for naming the items (files, folders) - names which are also character encoded in UTF-16 and normalized to a form very nearly the same as Unicode Normalization Form D (NFD) (which means that precomposed characters like é are decomposed in the HFS+ filename and therefore count as two characters and UTF-16 implies that characters from outside the Basic Multilingual Plane - often seldom used and characters from ancient writing systems - also count as two characters in an HFS+ filename). HFS Plus permits filenames up to 255 UTF-16 characters in length, and n-forked files similar to NTFS, though until recently, almost no software takes advantage of forks other than the data fork and resource fork. HFS+ also uses a full 32-bit allocation mapping table, rather than HFS’s 16 bits. This was a serious limitation of HFS, meaning that no disk could support more than 65,536 allocation blocks under HFS. When disks were small, this was of little consequence, but as larger-capacity drives became available, it meant that the smallest amount of space that any file could occupy (a single allocation block) became excessively large, wasting significant amounts of space. For example, on a 1 GB disk, the allocation block size under HFS is 16 KB, so even a 1 byte file would take up 16 KB of disk space.

Taken from the following article…"HFS." (Hierarchical File System) Definition. Web. 11 Oct. 2015.

4. Comparison of File and Directory Name and File Systems on Macintosh, PC and Unix Computers and Operating Systems:"Comparison of File and Directory Name and File Systems on Macintosh, PC and Unix Computers and Operating Systems." File Systems. Web. 11 Oct. 2015.

Mac OS file names compatibility:

• Mac OS9 supports HFS and HFS+ File system and may be up to 31 characters long. Max OSX supports HFS+ and UFS (Unix File System) and may be up to 255 characters long.

• Colon ":" is used as a directory separator.

• File and folder names may use any characters except colon ":" and forward slash "/" which is used for directory separators on OS9 and OSX.

• Filenames preserves case but are not case sensitive.

Windows file names compatibility:

• Windows uses two different file systems: File Allocation Table (FAT) file system and New Technology File System (NTFS).

• File and folder names may be up to 255 characters long on FAT file systems and 256 characters long on NTFS. Full pathnames may be up to 260 characters long.

• There is a limit to the full pathnames of 260 characters long.

• Backslash "\" is used as the directory separator.

• File and directory names may not contain the special characters: "/\*?<>|:

• Periods are allowed in file and directory names, but not as the last character. for example "letter.doc" is legal but "letterdoc." is an illegal file name.

• Filenames preserves case but are not case sensitive.

UNIX file names compatibility:

• Unix base operating systems mostly use the UFS (Unix File System).

• File and folder names may be up to 255 characters long.

• Forward slash"/" is used as the directory separator.

• File and directory names may not contain the special characters: space and /

• Filenames preserves case and are case sensitive.

5. Mac OS X: Mac OS Extended format (HFS Plus) volume and file limits

Learn the limits for files and volumes on disks that use the Mac OS Extended format (HFS Plus) in Mac OS X, including journaled, encrypted, and case-sensitive volumes.

Notes

1. The theoretical maximum file size for a Mac OS Extended file system is millions of terabytes. In practice, the maximum file size is equivalent to the maximum volume size, except for a small amount of disk space reserved for file system information.

2. Specifically, 2^31, or 2,147,483,648. However, the actual number of files that can be stored on a Mac OS Extended (HFS Plus) or journaled HFS+ volume depends on the volume's size and the size of the files. For example, a 160 GB Mac OS Extended volume with the default block size of 4 KB has 40 million available blocks. This volume could store up to 40 million very small files, but not 2 billion. A bigger disk with the same default block size could hold proportionately more files.

3. 2^63 - 2^31 = 9,223,372,034,707,292,160, which is just under 8 exabytes (EB). One exabyte is roughly equivalent to one million terabytes.

Last Modified: Feb 12, 2015

"Apple." Mac OS X: Mac OS Extended Format (HFS Plus) Volume and File Limits. Web. 11 Oct. 2015.

As you may have noticed, I also threw in some extra information on the various volume and sizes of the systems. this may help with future decisions consernning which system to use.

Thank you for joining me today in learning more about the Apple.