List of floppy disk formats

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8-inch, 5 14-inch, and 3 12-inch floppy disks

This is a list of different floppy disk formats.

IBM 8-inch formats[edit]

This is a list of 8-inch floppy diskette formats as introduced by IBM.

Category Drive designation 23FD 33FD 43FD 53FD
Media designation N/A (read only) Type 1 Type 2 Type 2D
App. size 80 KB 242 KB 284 KB 303 KB 492 KB 568 KB 985 KB 1,136 KB 1,212 KB
Drive Heads (sides) 1 1 1 1 2 2 2 2 2
Spindle motor
speed (RPM)
90 360 360 360 360 360 360 360 360
Controller Transfer rate (kbit/s) 33.333 250 250 250 500 500 500 500 500
Encoding FM FM FM FM FM FM MFM MFM MFM
Media Track density (TPI) 32 48 48 48 48 48 48 48 48
Bit Density (BPI) 1,594 3,268 3,268 3,268 3,408 3,408 6,816 6,816 6,816
Density designation SS SD SS SD SS SD SS SD DS SD DS SD DS DD DS DD DS DD
Geometry of the
index cylinder (0)
Sectors N/A 26 26 26 26 26 26 26
Sector size (bytes) 128 128 128 128 (side 0:128
1:256)
(side 0:128
1:256)
(side 0:128
1:256)
Size (bytes) N/A N/A 3,328 3,328 6,656 6,656 9,984 9,984 9,984
Geometry of
remaining cylinders
Usable cylinders 32 73 74 74 74 74 74 74 74
Sectors per track 8 26 15 8 26 15 26 15 8
Number of sectors 256 1,898 1,110 592 3,848 2,220 3,848 2,220 1,184
Sector size (bytes) 319 128 256 512 128 256 256 512 1024
Capacity Formatted (bytes) 81,664 242,944 284,160 303,104 492,544 568,320 985,088 1,136,640 1,212,416
Formatted (KB) 79.75 237.25 277.5 296 481 555 962 1,110 1,184
SS = Single Sided; DS = Double Sided; SD = Single Density; DD = Double Density; N/A = Not Applicable; TPI = Tracks per Inch; BPI = Bits per Inch

DEC 8-inch formats[edit]

Digital Equipment Corporation used the following formats on 8-inch disks:

Category Drive designation DEC RX01 DEC RX02
App. size 250 KB 500 KB
Drive Heads (data surfaces) 1 1
Spindle motor speed (RPM) 360 360
Controller Transfer rate (kbit/s) 250 500
Encoding FM FM/MFM
Media Track density (TPI) 48 48
Bit density (BPI) 3,200 6,400
Density designation SS SD SS DD
Geometry Cylinders 77 77
Sectors per track 26 26
Total sectors per disk 2,002 2,002
Sector size (bytes) 128 256
Capacity Formatted (bytes) 256,256 512,512
Formatted (KB) 250.25 500.5
SS = Single Sided; SD = Single Density; DD = Double Density; TPI = Tracks per Inch; BPI = Bits per Inch

NOTE: "RX02 8 inch Floppy Drive Information". David Gesswein. Retrieved 2007-09-21.

The RX02 mode is not compatible with other standard drives since the headers are always in single density mode but the data is written in double density mode. Also in double density mode the standard MFM encoding was modified from the standard to prevent false header detection in data.

Other manufacturers[edit]

Disk Form factor[1] Year introduced Formatted
Storage capacity
(in KB = 1024 bytes if not stated)
Marketed
capacity¹
IBM 23FD[2] 8-inch 1971 79.75 ?
Memorex 650 8-inch 1972 175 1.5 megabit[3] [unformatted]
IBM 33FD / Shugart 901 8-inch - SSSD 1973 237.25[4][5] 3.1 Mbits unformatted
IBM 43FD / Shugart 850 8-inch - DSSD 1976 500.5[6] 6.2 Mbits unformatted
Shugart SA 400 5¼-inch (35 track) 1976[7] 87.5[8] 110 kB
IBM 53FD / Shugart 850 8-inch DSDD 1977 980 (CP/M)
- 1200 (MS-DOS FAT)
1.2 MB
5¼-inch DD 1978 360 or 800 360 KB
HP single sided 3½-inch 1982 280 264 kB
3-inch 1982[citation needed] 360[citation needed] ?
3½-inch (DD at release) 1984 720 720 KB
5¼-inch QD 720 720 KB
5¼-inch HD 1982 YE Data YD380[9] 1155 1.2 MB
3-inch DD 1984[citation needed] 720[citation needed] ?
Mitsumi Quick Disk 3-inch 1985 128 to 256 ?
2-inch 1985[citation needed] 720[citation needed] ?
5¼-inch Perpendicular 1986[citation needed] 100 MB[citation needed] ?
3½-inch HD 1987 1440 1.44 MB
3½-inch ED 1987[10] 2880 2.88 MB
Floptical (LS) 3½-inch 1991 20385 21 MB
LS-120 3½-inch 1996 120.375 MB 120 MB
LS-240 3½-inch 1997 240.75 MB 240 MB
HiFD 3½-inch 1998/99 150/200 MB[citation needed] 150/200 MB
Abbreviations: DD = Double Density; QD = Quad Density; HD = High Density; ED = Extended Density; LS = Laser Servo; HiFD = High capacity Floppy Disk; SS = Single Sided; DS = Double Sided

The formatted capacities of floppy disks is less than the unformatted capacity, which does not include the sector and track headings required for use of the disk. The amount of capacity lost to this overhead depends on the application of the drive and is beyond the manufacturer's control. Mixtures of decimal SI-style prefixes and binary record lengths required care to properly calculate total capacity. Unlike semiconductor memory, which doubled in size each time an address pin was added to an integrated circuit package and so naturally favored counts that were powers of two, the capacity of a disk drive was the product of the sector size, number of sectors per track, number of tracks per side, (and in hard drives, the number of disk platters in the drive). Individual formatted sector lengths are arbitrarily set as powers of 2 (256 bytes, 512 bytes, etc.), and disk capacity is naturally calculated as multiples of the sector size. This led to an impure combination of decimal multiples of sectors and binary sector sizes. The "1.44 MB" value for the 3½-inch HD floppies is the most widely known example; where the "M" prefix is peculiar to the context of the disk drive and represents neither a decimal million nor a mebibyte 2 ^20. See Ultimate capacity and speed.

Dates and capacities marked ? are of unclear origin and need source information; other listed capacities refer to:

Formatted Storage Capacity is total size of all sectors on the disk:

  • For 8-inch see Table of 8-inch floppy formats IBM 8-inch formats. Note that spare, hidden and otherwise reserved sectors are included in this number.
  • For 5¼- and 3½-inch capacities quoted are from subsystem or system vendor statements.

Marketed Capacity is the capacity, typically unformatted, by the original media OEM vendor or in the case of IBM media, the first OEM thereafter. Other formats may get more or less capacity from the same drives and disks.

Physical composition[edit]

Floppy disk physical characteristics
(capacity and tracks are nominal, per side)
Size Density Tracks TPI BPI Coercivity Unformatted capacity per side
3½-inch single 40 67.5 600 Oe 250 KB
double 80 135 8.717 600 Oe (300 Oe) 500 KB
high 80 135 17.434 750 Oe (600 Oe) 1000 KB
extended 80 135 900 Oe 2000 KB
5¼-inch single/double 40 48 5.876 300 Oe 250 KB
quad 80 96 5.876 300 Oe 500 KB
high 80 96 8.646 600 Oe 750 KB
8-inch single/double 77 48 300 Oe 1000 KB

Known disk logical formats[edit]

Throughout the 1970s and 1980s, many different logical disk formats were used, depending on the hardware platform.

Common floppy disk formats, logical characteristics by platform
Platform Size Density Bytes/ sector Sectors/ track Tracks/ side Sides Capacity RPM Encoding Note
IBM (3740 format) 8-inch single 128 26 74 (73) 1 240.5 KB (237.25 KB) 360 FM [11]
Acorn 5¼-inch single 256 10 40 1 100 KB 300 FM
80 200 KB
double 256 16 40 1 160 KB MFM
80 320 KB
2 640 KB
3½-inch (90 mm) double 256 16 80 2 640 KB 300 MFM
1024 5 800 KB
high 10 1600 KB
Apple II 5¼-inch double 256 13 35 1 113.75 KB 300 GCR [12]
2 227.50 KB
16 1 140 KB
2 280 KB
3½-inch (90 mm) double 512 Variable (8-12) 80 1 400 KB CLV GCR [13]
2 800 KB
high 512 18 80 2 1440 KB 300 MFM [14]
Apple Lisa 5¼-inch (FireWare) double 512  ?  ? 2 860K 218 - 320 GCR
Apple Macintosh 3½-inch (90 mm) double 512 Variable (8-12) 80 1 400 KB CLV GCR
2 800 KB
high 512 18 80 2 1440 KB 300 MFM
Atari 8-bit 5¼-inch single 128 18 40 1 90 KB 288 FM [15]
enhanced 128 26 130 KB MFM
double 256 18 180 KB
Atari ST/TT/Falcon 3½-inch (90 mm) double 512 9 80 1 360 KB 300 MFM
2 720 KB
high 18 1440 KB
Commodore (8-bit) 5¼-inch double 256 Variable (17-21) ZCAV 35 1 170 KB 300 GCR [16]
2 340 KB
quad Variable (23-29) ZCAV 77 1 521 KB
2 1042 KB
3½-inch (90 mm) double 512 10 80 2 800 KB MFM  
Commodore Amiga 3½-inch (90 mm) double 512 11 80 2 880 KB 300 MFM [17]
high 22 1760 KB 150
IBM PC compatibles[18] 8-inch single 128 26 77 1 250.25 KB[19][20][21][22] 360 MFM [23]
2 500.5 KB[19][20][21][22]
double 1024 8 1 616 KB[19][21][22]
2 1232 KB[19][20][21][22]
5¼-inch double 512 8 40 1 160 KB[19] 300 MFM  
2 320 KB[19]
9 1 180 KB[19]
2 360 KB[19]
unknown 8 80 1 320 KB[19] unknown
2 640 KB[19]
high 15 80 2 1200 KB[19] 360
3½-inch (90 mm) double 512 8 80 1 320 KB[19] 300 MFM
9 360 KB[19]
8 2 640 KB[19]
9 720 KB[19]
high 18 1440 KB[19]
21 1680 KB[19] DMF[24]
82 1720 KB[19]
extended 36 80 2880 KB[19]
MGT SAM Coupé 3½-inch (90 mm) double 512 10 80 2 800KB 300 MFM  
NEC PC98 8-inch single 128 26 77 1 250.25 KB[19] 360 FM  
double 1024 8 77 2 1232 KB[19] MFM
5¼-inch double 512 8 80 2 640 KB[19] 360 MFM
9 720 KB[19]
high 15 1200 KiB[19]
1024 8 77 (80)[25] 1232 (1280) KB[19][25] [25]
3½-inch (90 mm) double 512 8 80 2 640 KB[19] 360 MFM
9 720 KB[19]
high 15 1200 KB[19] 3mode[26][25]
1024 8 77 (80)[25] 1232 (1280) KB[19][25]
512 18 80 1440 KB[19] 300
SHARP X68000 5¼-inch high 1024 8 77 2 1232 KB[19] 360 MFM  
3½-inch (90 mm)

Notes and references[edit]

  1. ^ Floppy disk sizes are almost universally referred to in inch measurements, even in countries where metric is the standard, and even when the size is in fact defined in SI; for instance, the 3½-inch floppy is defined as 90 mm.
  2. ^ James T. Engh (September 1981). "The IBM Diskette and Diskette Drive". IBM Journal of Research and Development 25 (5): 701–710. doi:10.1147/rd.255.0701. Retrieved 2008-07-14. 
  3. ^ Memorex 650 Flexible Disc File - OEM Manual
  4. ^ The IBM Diskette and Diskette Drive, James T. Engh, 1981 - "The user capacity of the diskette was established at 242 944 bytes on 73 tracks with 26 sectors on each track."
  5. ^ The Evolution of Magnetic Storage, L.D. Stevens, 1981 - "This drive, with a capacity of 243 Kbytes"
  6. ^ The IBM Diskette and Diskette Drive, James T. Engh, 1981 - "This would double the capacity to approximately 0.5 megabytes (Mbytes)."
  7. ^ Sollman, George (July 1978). "Evolution of the Minifloppy (TM) Product Family". Magnetics, IEEE Transactions on 14 (4): 160–166. doi:10.1109/TMAG.1978.1059748.  "In September, 1976, the first minifloppy disk drive was introduced by Shugart Associates."
  8. ^ Shugart SA 400 Datasheet Formatted with 256 byte sectors and 10 sectors per track the capacity is 89.6 Kbytes (256 x 10 x 35 = 89,600), or 87.5 KB
  9. ^ per 1986 Disk/Trend Report, Flexible Disk Drives
  10. ^ Mueller, S: "Upgrading and Repairing PCs", p.656, Que Publishing, 2002.
  11. ^ They have 73 data tracks, 1 index track, 2 spare tracks, 1 reserved track
  12. ^ 16 sector filesystems require a compatible disk controller (PROM update) and Apple DOS 3.3 or later
  13. ^ Apple II double-density 3½-inch (90 mm) drives use variable sectors sizes (tracks 00-15: 12 sectors, tracks 16-31: 11 sectors, tracks 32-47: 10 sectors, tracks 48-63: 9 sectors, tracks 64-79: 8 sectors)
  14. ^ Apple II high-density 3½-inch (90 mm) drives require a compatible disk controller and ProDOS 8.
  15. ^ Atari XF551 uses 360K, 300RPM, MFM, Double Side/Double Density.
  16. ^ Commodore floppy drives used a fixed rotation speed with variable sector density (see: Zone bit recording)
  17. ^ Though the Amiga used MFM, the format places sectors too close together for a standard IBM PC compatible floppy disk controller to read (appearing as one 5632-byte physical sector per track).
  18. ^ Standard Floppy Disk Formats Supported by MS-DOS
  19. ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae The calculated formatted capacity is based on FAT12 format.
  20. ^ a b c "Standard Floppy Disk Formats Supported by MS-DOS". 2.0. Microsoft Help and Support. 2003-05-12. Retrieved 2012-09-11. 
  21. ^ a b c d Ray Duncan (1988). The MS-DOS Encyclopedia - version 1.0 through 3.2. Microsoft Press. ISBN 1-55615-049-0.
  22. ^ a b c d Xerox (1983-11). Xerox 16/8 Professional Computer - MS-DOS OS Handbook for 8" Floppy Disks. 1983-11, MS-DOS 2.0 ([1])
  23. ^ While IBM didn't include an 8" floppy drive option on any of their PCs and PC DOS, MS-DOS 1.25 supported 8" disks and added support for higher capacities in version 2.0. MS-DOS' predecessor 86-DOS used 8" diskettes as well.
  24. ^ These variations are known as DMF diskettes, used for a time to pack more data on to each disk for software distribution.
  25. ^ a b c d e f Inner 3 tracks of 8 sectors/track format are unused.
  26. ^ The PC98 3½" (90 mm) formats are also known as "3 Mode" floppy disks, usable on IBM PC compatibles with a 3-mode floppy drive.

External links[edit]