Apple's extended-format files are part of the Mac HFS Plus, or HFS+, file hierarchy. HFS Plus has replaced Apple's previous Hierarchical File System as the standard Mac filing system. HFS Plus allows substantially larger files because it uses a 32-bit allocation system for file addresses, which allows it to allocate a larger chunk of hard-drive space to each file's contents.
Volumes
- In computer terms, a volume is either a storage device, such as a hard disk, backup disk or CD, or spaces on a storage device if you partition them into multiple volumes. At one point, the largest volume a Mac could accept was 2 GB, but Apple adjusted its operating systems so that, as of the time of publication, they allow up to 4 GB. The maximum number of files in a volume depends on the size of the volume and of the files: A 4 GB volume made up of 4K blocks can hold 1 million one-block files, for instance.
Volume Size
- If you're working on a Mac with an older operating system -- OS 8.5 or any version of OS9 -- it starts up with a maximum of 20 volumes, or storage areas on the disk, plus the start-up volume. You may be able to add volumes using Disk Utility, provided your computer isn't too busy to handle them. The maximum volume size for OS 8.5 or 9 is 2 TB, or terabytes.
File Size
- The maximum size of an individual file on a Mac OS 8 is 2 GB, while OS 9 can go up to 2 TB. On OS X, the limit to file and volume size is 2 TB for 10 and 10.1, then rises to 8 TB for 10.2, 16 TB for 10.3 and 8 EB, or exabytes, for 10.4 and beyond. An exabyte equals a million terabytes. In order to store a really large file, you must have a volume of equal or greater size.
Considerations
- As of the time of publication, the number of files you can store in a volume on OS X is, potentially, 2.1 billion, though the size of the files and the volume may reduce the maximum in practice. On OS 8 and 9, the maximum number of files is 2 billion, with 32,767 in any given volume. HFS Plus disks include several special files, such as an allocation file specifying whether a particular block is free.
