The floppy disk is quite popular. It is a ubiquitous data storage and transfer device. It is said to be from the mid-1970s well into the 2000s. And apart from the 8-inch format that preceded the 5¼ -inch and the 31/2-inch formats that happened to be used in IBM PC compatible systems, many proprietary floppy disk formats were known to be developed either using a different disk design or just a special layout or encoding methods for the information stored inside the disk.
The Commodore 64/128
According to reports, Commodore were said to begin its tradition of special disk formats with the known 51/4 -inch disk drives. The 51/4 inch disk drives were accompanying its PET/CBM, VIC-20, and also the Commodore 64 home computers. We should also note that they are the same as the 1540 and 1541 drives used with the VIC-20 and the Commodore 64. And we need to know that the standard Commodore Group Code Recording (GCR) scheme that was used in 1541 and compatibles employed four different data rates depending upon track position.
As being unique among computer architectures, the operating system on the computer is said to be unaware of the details of the disk and file system. Disk operations are handled by what is called Commodore Dos which was actually implemented with an extra MOS-6502 processor on the disk drive. But the fact remain that, many programs like GEOS actually bypass Commodore’s DOS completely. And not only that, but replace it with fast loading programs in the 1541 drive.
At long last, Commodore later gave in to disk format standardization and made its last drives that are 51/4 inch (i.e. the 1570 and the 1571) and are compatible with what is known as Modified Frequency Modulation. This is meant to enable the Commodore 128 to work with CP/M disks from different vendors. The C128 (that was equipped with one of those drives) were able to access both C64 and CP/M disks. Well, it needs to (as well as MS-DOS disks- using third-party software). And this happens to be a crucial feature for some office work. And also, Commodore developed a 31/2 -inch 800 KB disk format for its 8-bit machines with the 1581 disk drive (which of course, only uses Modified Frequency Modulation).
We need also know that the GEOS operating system uses a disk format that is known to be largely identical to the Commodore DOS format (though with a very minor extension). But generally, it was compatible with standard Commodore disks. Nevertheless, certain disk maintenance operations can corrupt the file system without proper supervision from the GEOS kernel.
As a matter of fact, the Commodore Amiga computers use an 880 KB format on a 31/2 floppy. And the intersector gaps can be eliminated to save space, the entire track is written at once. The Amiga floppy controller is known to be basic. It is said to be much more flexible than the one on the PC. You know, it is free of arbitrary format restrictions, and also encoding such as GCR and MFM that can be done in software. Also, developers were even able to create their own proprietary disk formats.
And then, because of that, foreign formats as the IBM PC-compatible can then be handled with ease. This is by use of what is known as CrossDos, which was known to be included with later versions of AmigaOS. One other thing we should know is that an Amiga can theoretically read any arbitrary format on the 31/2 -inch floppy, with the correct file system driver. Nevertheless, on the PC, there is no way to read an Amiga disk without certain special hardware and a second floppy drive. And one of the special hardware that enables an Amiga disk to be read on a PC is a CatWeasel.
A flippy (a flippy disk) is actually a double-sided 5 1/4 inch floppy disk. Flippy disks are reputed to be specifically designed such that the two sides can be used independently in single-sided drives. It should be noted that they can only be used independently in single-sided drives and not simultaneously.
The flippy modification required that an entirely new write-enable notch be cut if the disk was written to- that is for disk OS that do not require that the disk index hole mark the beginnings of tracks. And for the purpose, disk doublers (which are single-rectangular-hole punchers that are specially produced) and are sold by third-party computer accessory manufacturers).