Hierarchical File System is an obsolete data storage format created by Apple and used on Macintosh computers. HFS was first introduced in 1985 and used until Apple introduced HFS+ in 1998 to phase out and replace the aging file system. According to "Practical File System Design" author Dominic Giampaolo, the original HFS is not equipped to efficiently handle data on storage devices with more than 1GB of space.

HFS Volume Limitations

HFS can allocate logical volumes on storage devices as large as 2TB. A logical volume is an allocation of physical space as a unit on a storage device. HFS volume size limits are also limited by the computer's operating system. Mac OS 6 and 7 computers can only address HFS volumes as large as 2GB and OS 7.5 bumped the capacity to 4GB. As of the OS 7.5.2 revision, all Mac computers can address HFS volumes of up to 2TB in size. Computer users can work around the maximum volume sizes by creating several HFS volumes on the same storage device.

HFS File Limitations

While HFS volume sizes increased with operating system revisions, the maximum size of an individual file did not. Files stored on a HFS-formatted drive can't exceed 2GB in size. Additionally, HFS volumes can only store up to 54,536 individual files and up to 32,767 files within a single folder.

HFS Block Size Problems

HFS supports a maximum of 65.535 allocation blocks on a single storage device volume. HFS divides the storage device space into equal-sized individual blocks the computer uses to identify where data files begin and end. The larger the hard drive, the larger the block size. Since new files can only start in unused blocks, any unused space in a block occupied by another file can't be used. A 4KB file will take up 64KB of space on a volume formatted with 64KB blocks.

HFS+ Extended Improvements

Apple's HFS+ is designed to replace HFS on modern hard drives extending into the terabyte and beyond storage range. HFS+ can store up to 2.1 billion individual files and folders on a single volume. Additionally, HFS+ supports massive maximum volume and file sizes extending up to 8 extabytes. However, the maximum volume and file sizes are limited by operating system version: OS 10 has a cap of 2TB, OS 10.2 increased the cap to 8TB, OS 10.3 can address up to 16TB and OS 10.4 can use the full 8EB.