Not sure why I started thinking about this today, but here it is…
Floppy disks were removable media, in various formats and sizes, used in the 70’s through 90’s.
Floppy disks consisted of a single-layer, thin plastic substrate covered in magnetic particles, plus its dust jacket with various apertures for read/write, index, and read-only mode.
Floppy disks were called “floppy” because both the substrate and the dust jacket of the 8″ and 5.25″ media were flexible.
Later, the 3.5″ format employed a non-flexible, cartridge format for the dust jacket, sparking the misnomer “hard disk”. It was common in the 90’s for people to say “I saved it on the hard disk” when they really meant 3.5″ floppy disk (a removable storage cartridge), rather than “hard drive” (a fixed-media, high-density secondary storage device inside the machine)
Hard-sectored vs soft-sectored
For 8″ and 5.25″ disks, hard-sectored means that there were multiple index holes in the disk, while soft-sectored means that there is only one index hole in the disk itself. The index hole is read through the index hole of the dust jacket. If you use two fingers against the inner edge of the hub, to gently spin the floppy within its jacket, you will eventually see the index hole (or holes) in the disk substrate line up with the index hole in the dust jacket.
I think all 3.5″ disks were explicitly soft-sectored, indexed by the drive latch hole in the hub.
It was not uncommon for a specific floppy disk media to come in multiple formats.
Disks could be single-sided (SS), meaning only one side (usually the bottom) is writable, or double-sided (DS), meaning that both the top and the bottom are writable.
Disks came in various densities, including single density (SD), double density (DD), and high-density (HD).
8″ and 5.25″ disks could be single or double sided. Some computer systems could only read or write to one side (usually the bottom), so punching an extra read-write hole on the edge allowed the disk to be inserted topside-down, to leverage the opposite writable surface. I assume that drives set up for this had an extra sensor to account for the index hole being transposed — most “double-sided” 5.25″ disks didn’t have two index holes in the dust jacket.
3.5″ disks were explicitly double-sided.
- 8″ DSDD “Double Sided, Double Density”, 1.2 meg. Used in the late 70’s and early 80’s, most notably in the Tandy TRS-80 systems.
- 5.25″ SSSD “Single Sided, Single Density”, 90K, and DSSD, 180K.
- 5.25″ DSDD “Double Sided, Double Density”, 360K. This was the standard format for most microcomputers during the 80’s.
- 5.25″ DSHD “Double Sided, High Density”, 1.2 meg. This format was designed to extend the life of the 5.25″ form factor, as data storage requirements increased. This format was not very common, as the 5.25″ form factor was largely replaced with the 3.5″ form factor in the late 80’s — the 3.5″ DSHD format was more convenient to carry, and held slightly more data.
- 3.5″ DSDD, 720K. Used in the late 80’s and early 90’s.
- 3.5″ DSHD, 1.44 meg. This was the standard format for most PCs from about 1993 onward.
- The original IBM PC shipped with the 360K DSDD 5.25″ floppy format. Many other manufacturers, including Apple, Atari, and Commodore supported the same format, making it a defacto standard.
- The IBM PC-AT had an option for the 1.2 meg DSHD 5.25″ floppy format. This format was not widely adopted due to the prevalence of 360K drives and media.
- The IBM PS/2 series was introduced with the 3.5″ DSDD (720K) and DSHD (1.44 meg) formats. IBM drives supporting the DSHD format had “1.44” written on the disk-eject button.
- All 5.25″ floppies, including the 1.2 meg format, were largely phased out by the early 90’s. Most people either used 5.25″ or 3.5″ but not both.
- TEAC sold a “dual media” drive, that was really two floppy drives inside a single 1/2 height (and later, 1/3 height) housing. The 1.2 meg 5.25″ slot was on top, and used a standard 5.25″ lever-style lock, while the 1.44 meg 3.5″ slot was just below it, using a standard eject button.
- Amiga, Apple Macintosh, and Sun, among others, used the 3.5″ floppy format.
- Sun had an “eject” binary whose sole purpose was to eject the floppy disk from its housing, as the Sun drive didn’t have a manual eject button.
- Due to the demand for increased storage capacity, floppies were eventually phased out. Other cartridge-based systems such as the Syquest EZ-135, Iomega ZIP drive, and Imation LS-120 provided high-speed, high-capacity, removable cartridges.
- In the late 90’s and early 2000’s, many computer systems included either internal ZIP or LS-120 drives as the primary removable media.
- Re-writable CD drives and USB flash drives eventually replaced floppies and cartridge-based schemes.
- Each Floppy Drive Controller (FDC) could support 2 drives. A standard floppy cable had a twist after the first connector, called the “address twist”. The first device (or A: drive) was at the end of the cable (above the address twist), while the second device (or B: drive) was below the address twist.
- Older cables had only edge-style connectors used by 5.25″ drives, requiring a pin-to-edge adapter for 3.5″ drives. Later, most cables included both connector styles in both the “A” and “B” positions, so that either type of drive could be connected in either position. As 5.25″ was phased out, floppy cables eventually ONLY supported the 3.5″ pin-style connector.