Floppy disk

Latest revision as of 11:41, 5 September 2024

See also Filesystems, which are contained on Floppy Disks.

Formats for images of floppy disk data can be found at Disk Image Formats.

The main ways in which floppy disks could differ at a recording level:

• The physical dimensions and physical layout – the most common sizes were 8-inch, 5¼-inch (officially the metric 130 mm, but in common parlance referred to by its inch approximation even in countries which normally use the metric system), 3½ inch (likewise officially metric 90 mm, but commonly known by the inch approximation). Note those are the sizes of the actual magnetic disk, the jacket/cartridge is larger. However, there were many other rare sizes.
• The method of data encoding: the earliest floppies IBM 8-inch floppies used FM encoding. Capacity was doubled, without changing the disks physically, by switching to the more efficient MFM encoding. The original FM encoded disks were called "single density", and the MFM encoded "double density". IBM PC 5¼-inch and 3½ inch floppies used MFM encoding; the term "double density" was later extended to "high density" and beyond, but this time it referred to changes in the magnetic material and type of disk heads rather than an encoding change. GCR encoding was also popular, particularly with systems such as Apple IIs and Commodore 64s. Some early "double density" drives used M2FM encoding (most notably Intel ISIS-II and HP 9885) which was later replaced by the simpler MFM.
• Magnetic recording material: more expensive media could store more data
• Type of magnetic disk heads: more expensive magnets could store more data
• Speed of rotation
• Constant angular velocity (CAV) versus constant linear velocity (CLV)
• Number of sides – early disks and drives were single-sided only and could only record on one side of the disk; later disks and drives were double-sided and supported recording on both sides. There were also "flippy disks" where a single-sided drive could be used to record on both sides of a disk by the user manually flipping the disk to access the other side.
• Longitudinal magnetic recording versus perpendicular magnetic recording: traditionally floppies used longitudinal; 2.88 MB floppy drives doubled the capacity over 1.44MB by switching to perpendicular
• Sector size: the earliest floppies had 128 byte sectors; IBM PC floppies normally had 512 byte sectors. IBM PC floppy controllers could support any power of 2 from 128 to 4096. Rarely, different tracks on a floppy could be recorded with different sector sizes, or even a single track with a mix of different sector sizes.
• Gap length between sectors: reducing the gap length could squeeze more sectors on to the disk but at the risk of data loss
• Format of track and sector headers, including CRC algorithms and any per-sector flags (e.g. IBM 3740 has a flag to mark each sector as "deleted", a feature carried forward into IBM PC floppy formats, but almost never used in them.)
• Number of tracks per disk and number of sectors per track

A given combination of floppy disk controller, floppy drive, and disk, could generally support several different variations on the same basic format, but only within certain constraints – e.g. IBM PC floppies could be formatted with a non-standard sector size or number of tracks, but not with GCR or MMFM encoding (since the floppy disk controllers used in IBM PCs did not support those encodings).

The disk geometry, encoding, etc, is orthogonal to the filesystem – 1.44MB Apple Mac floppies were physically interoperable with IBM PC floppies, even though IBM PCs normally lacked software to read Apple's HFS filesystem; by contrast, the earlier 800KB and 400KB Apple Mac floppies were incompatible with IBM PC floppies, since IBM PC floppy drives could not physically read them, nor could those earlier Mac floppy drives physically read IBM PC floppies.

[edit] 2 Inch

• LT-1
• Video Floppy

[edit] 2 1/2 Inch

• Sharp 2.5-inch floppy disk

[edit] 3 Inch

• CF-2 Compact Floppy Disk
• MCD-1 Micro Cassette

[edit] 3 1/2 Inch

• Acorn
  • Acorn double density 3 1/2" disk
  • Acorn high density 3 1/2" disk
• Akai Disk Format
• Amiga
  • Amiga double density disk
  • Amiga high density disk
• Apple
  • Apple double-density 3 1/2" disk
  • Apple high-density 3 1/2" disk
• Brother
  • Brother 120k
  • Brother 240k
  • Brother HD
• Commodore
  • Commodore 1581 disk
• IBM PC and compatibles
  • PC-DOS 720K format
  • PC-DOS 1.44M format
  • PC-DOS 2.88M format
• SAM Coupé
  • SAM Coupé disk
• ZX Spectrum
  • ZX Spectrum Beta Disc 3.5" floppy (see TR-DOS filesystem)

[edit] 4 Inch

• IBM DemiDiskette

[edit] 5 1/4 Inch

• Acorn
  • Acorn single density 5 1/4" disk
  • Acorn double density 5 1/4" disk
• APF
  • APF Imagination Machine floppy disk
• Apple
  • Apple II 13 sector disk (Apple DOS 3.2)
  • Apple II 16 sector disk (Apple DOS 3.3, ProDOS, Apple III SOS)
  • Twiggy floppy (Apple Lisa)
• Atari
  • Atari 810
• CalComp
  • CalComp Vistagraphic 4500 floppy disk
• Commodore
  • Commodore 2040 disk (and 4040; for PET computers; preceded 1541 despite higher number)
  • Commodore 1541 disk (used with VIC-20 and C-64)
  • Commodore 1571 disk (used with C-128)
• Compucolor
  • Compucolor II disk
• IBM PC and compatible
  • PC-DOS 160K format
  • PC-DOS 180K format
  • PC-DOS 320K format
  • PC-DOS 360K format
  • PC-DOS 1.2M format
• Kaypro
  • Kaypro 2 CP/M 2.2
  • Kaypro 4 CP/M 2.2
• North Star
  • North Star MDS-A-D
• PMC
  • PMC MicroMate floppy disk
• Tandy
  • TRS-80 Model I, III, 4
    • TRS-80 single density 5.25" disk
    • TRS-80 double density 5.25" disk
  • TRS-80 Color Computer
    • TRS-80 Color Computer single sided 5.25" disk
    • TRS-80 Color Computer double sided 5.25" disk
• Texas Instruments
  • TI-99/4A 90K
  • TI-99/4A 180K
  • TI-99/4A 360K
• ZX Spectrum
  • ZX Spectrum Beta Disc 5.25" floppy (see TR-DOS filesystem)

[edit] 8 Inch

Some 8" floppy disks

• DEC
  • DEC RX01
  • DEC RX02
• IBM
  • IBM Type 1 (33FD)
  • IBM Type 2 (43FD)
  • IBM Type 2D (53FD)
  • IBM 23FD
  • IBM 3740 format

[edit] Data encoding formats

• FM encoding
• GCR encoding
• MFM encoding
• RLL encoding

[edit] Devices to read floppy disks

• Device Side Data FC5025 USB 5.25" floppy controller
• KryoFlux
• DiskFerret
• Catweasel
• SuperCard Pro
• FluxEngine

[edit] Disk transfer info

• Info on disk transfers between Apple II and PC/Mac
• XFER STN (New Museum) (available to artists for converting old-format works)
• PC-Lect, program to read old disk formats (for PC/MS-DOS; doesn't work in Windows past Win98)

[edit] Utilities

• disktype: detect format of disk or disk image
• Floppy Disk Format Identifer Tool

[edit] Other links and references

• List of Floppy Disk Formats, Wikipedia.
• Digitize the Planet: Floppy Disks
• Michael Haardt et al's Floppy User Guide has some information on physical, magnetic, etc formats.
• Floppy drive tech info
• Commodore copy protection books and manuals
• Rescuing Floppy Disks (Archive Team)
• Care of diskettes
• Floppy disk archaeology lecture (video)
• Dealing with difficult disks and drives
• New, Improved Obamacare Program Released On 35 Floppy Disks (The Onion; humor)
• What are the Windows A: and B: drives used for?
• The Flippy Disk Thing
• Imaging 5.25" floppies
• This could take a while...
• Previously Unknown Warhol Works Discovered on Floppy Disks from 1985
• Detailed report on the Warhol graphic recovery (PDF)
• One of the computers that would receive a nuclear launch order from the President still uses 8" floppy disks.
• Library of Congress Recommended Format Specifications: Software/Gaming
• What settings should be used when imaging floppy disks using a Kryoflux device?
• Spreadsheet of floppy formats and Kryoflux settings
• Kryoflux Disk ID software; tries to identify disk types in image
• Bulk disk imaging and disk-format identification with KryoFlux
• Zip Disks & Floppies: musical piece by artist who formerly used those media for storing beats
• Notes on copy protection of Dungeon Master and Chaos Strikes Back for Atari ST and Amiga
• Windows 10 Preview Removes Floppy Disk Drive Support
• Some discussion of Shugart 801 8" drive
• How Star Trek creator Gene Roddenberry’s words were freed from old floppy disks
• An 8″ Floppy Disk Challenge
• Digital Obsolescence: Reproducing Floppy Data Cables
• The 8-Bit Guy: How Old School Floppy Drives Worked (video)
• Working with Floppy Disks from the 1980s

See also Disk Imaging Software & Systems.