Information is stored in separate blocks, where each block is composed of 512 bytes. On the original machine that is, as floppy disk drives were pretty slow. As with the directory cache mode all information was stored in one (or more when necessary) block, it was faster at listing directory content. This meant that in older OS versions the header of each file needed to be loaded to list all files in that directory. In older versions, the directory header only stored pointers to the files in that directory. With the direct cache mode, one or more blocks are stored for each directory (including the root) with basic information about the files stored in that directory. With Amiga OS 3.0, the ‘ directory cache mode’ was introduced. In combination with the ‘directory cache mode’ (see below), the international mode is mandatory. This mistake was corrected in OS 2.0, but is optional. The Amiga uses the ISO 8859 Latin-1 character set, where in older operating systems (<2.0), international characters (e.g., ‘ø’) were not capitalised. For that purpose, file names are shifted to upper case in file name matching routines. But during file name matching, the case is ignored. On the Amiga file names can have both lower and upper case characters. This mode was meant to correct for a mistake in the routine to convert text into upper case. In OS version 2.0 the ‘international mode’ was also introduced. So disks formatted with this file systems cannot be read by Amiga OS versions <2.0. The FFS does not have backward compatability. This advantage was dropped with the FFS making it slightly faster (on original machines) and gaining disk space for file data.
The OFS sacrifices disk space for validation purposes, making it more robust in case of data recovery when a disk got damaged. The previous file system was not named at the time, but is now commonly referred to as the Old File System (OFS).
With Amiga OS version 2.0, the so-called Fast File System (FFS) was introduced.
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