Floppy disk based systems organise data on the media in different ways.
Some examples of possible variations are:
- Physical Encoding
- Number of blocks
- Data/value representation
- Header information (current Track number, head number, data size, etc.)
- Location and method of integrity information
- Location and value of the Sync (aka Mark)
- Location, value and size of Gap
- Location and size of actual data part
You can see how these combinations are combined to form the structure of the AmigaDOS format as described in our disk structure description language in the July 2002 WIP.
This is simply just layout (aka geometry) information. Computer designers would either create their own format, or they would use an existing one depending on what hardware they had in their system. If they used a fully-fledged FDC (Floppy Disk Controller), the format had to conform to perdefined rules of geometry as allowed by that hardware.
The systems that did not have a fully-fledged FDC (like the Commodore Amiga) usually meant that the job of designing the floppy format moved from the hardware engineers to the software engineers, that is, it was defined in the operating system.
Games designers often tried to squeeze the very last drop out of the systems they were developing for. This often meant they had to go to drastic lengths to fit as much data as possible onto a floppy disk and one of they ways they could do this was to create a stream-lined disk format. As a better known example, using the “DiskSpare” utility on the Amiga meant you could store over 980 KiB on a floppy disk, as opposed to the normal AmigaDOS 880 KiB.
Of course, there are other reasons. Certainly the fact that it prevents the disk from being copied in a normal way would have been one of them.