These sectors are then grouped together into allocation blocks which can contain one or more sectors; the number of allocation blocks depends on the total size of the volume.
HFS Plus uses a larger value to address allocation blocks than HFS, 32 bits rather than 16 bits; this means it can access 4,294,967,296 (= 2 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.
HFS Plus also uses a full 32-bit allocation mapping table rather than HFS's 16 bits, significantly improving space utilization with large disks.
HFSX volumes are almost identical to HFS Plus volumes, except that they are never surrounded by the HFS Wrapper that is typical of HFS Plus volumes and they optionally support case sensitivity for file and folder names.
HFSX volumes can be recognized by two entries in the Volume Header, a value of HX in the signature field and 5 in the version field.
At WWDC 2017, Apple announced mac OS High Sierra, in which the default file system of Mac is changed to APFS.
HFS Plus 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 items.
With appropriate hardware, both encryption and decryption should be transparent.