List of floppy disk formats

This is a list of different floppy disk formats.

Contents

IBM 8-inch formats

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 (KiB) 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

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 (KiB) 250.25 500.5
SS = Single Sided; SD = Single Density; DD = Double Density; TPI = Tracks per Inch; BPI = Bits per Inch

Other manufacturers

Disk Form factor[1] Year introduced Formatted
Storage capacity
(in KiB = 1024 bytes if not stated)		 Marketed
capacity¹
IBM 23FD[2] 8-inch 1971 79.7 ?
Memorex 650 8-inch 1972 175 kB[3] 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] 89.6 kB[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 360 ?
3½-inch (DD at release) 1984 720 720 KB
5¼-inch QD 720 720 KB
5¼-inch HD 1982 YE Data YD380[9] 1,182,720 bytes 1.2 MB
3-inch DD 1984 720 ?
Mitsumi Quick Disk 3-inch 1985 128 to 256 ?
2-inch 1985 720 ?
5¼-inch Perpendicular 1986 100 MB ?
3½-inch HD 1987 1440 1.44 MB
3½-inch ED 1987[10] 2880 2.88 MB
Floptical (LS) 3½-inch 1991 21000 21 MB
LS-120 3½-inch 1996 120.375 MB 120 MB
LS-240 3½-inch 1997 240.75 MB 240 MB
3½-inch HiFD 1998/99 150/200 MB 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
¹ 

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

Floppy disk physical characteristics
(capacity and tracks are nominal, per side)
Size Density Tracks TPI BPI Coercivity Unformatted capacity per side
3½ in 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 in 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 in single/double 77 48 300 Oe 1000 KB

Known disk logical formats

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 in single 128 26 74 1 250.25 KiB 360 FM [11]
Acorn 5¼ in single 256 10 40 1 100 KiB 300 FM
80 200 KiB
double 256 16 40 1 160 KiB MFM
80 320 KiB
2 640 KiB
3½ in (90 mm) double 256 16 80 2 640 KiB 300 MFM
1024 5 800 KiB
high 10 1600 KiB
Apple II 5¼ in double 256 13 35 1 113.75 KiB 300 GCR [12]
2 227.50 KiB
16 1 140 KiB
2 280 KiB
3½ in (90 mm) double 512 Variable (8-12) 80 1 400 KiB ZCAV GCR [13]
2 800 KiB
high 512 18 80 2 1440 KiB 300 MFM [14]
Apple Macintosh 3½ in (90 mm) double 512 Variable (8-12) 80 1 400 KiB ZCAV GCR
2 800 KiB
high 512 18 80 2 1440 KiB 300 MFM
Atari 8-bit 5¼ in single 128 18 40 1 90 KiB 288 FM [15]
enhanced 128 26 127 KiB MFM
double 256 18 180 KiB
Commodore (8-bit) 5¼ in double 256 Variable (17-21) 35 1 170 KiB 300 GCR [16]
2 340 KiB
Commodore Amiga 3½ in (90 mm) double 512 11 80 2 880 KiB 300 MFM [17]
high 22 1760 KiB 150
IBM PC compatibles[18] 8 in single 128 26 77 1 250.25 KiB[19] 360 MFM [20]
2 500.5 KiB[19]
double 1024 8 2 1232 KiB[19]
5¼ in double 512 8 40 1 160 KiB[19] 300 MFM  
2 320 KiB[19]
9 1 180 KiB[19]
2 360 KiB[19]
unknown 8 80 1 320 KiB[19] unknown
2 640 KiB[19]
high 15 80 2 1200 KiB[19] 360
3½ in (90 mm) double 512 8 80 1 320 KiB[19] 300 MFM
2 640 KiB[19]
9 720 KiB[19]
high 18 80 1440 KiB[19]
21 80 1680 KiB[19] DMF[21]
82 1720 KiB[19]
extended 36 80 2880 KiB[19]
NEC PC98 8 in single 128 26 77 1 250.25 KiB[19] 360 FM  
double 1024 8 77 2 1232 KiB[19] MFM
5¼ in double 512 8 80 2 640 KiB[19] 360 MFM
9 720 KiB[19]
high 15 1200 KiB[19]
1024 8 77 (80)[22] 1232 (1280) KiB[19][22] [22]
3½ in (90 mm) double 512 8 80 2 640 KiB[19] 360 MFM
9 720 KiB[19]
high 15 1200 KiB[19] 3 mode[23][22]
1024 8 77 (80)[22] 1232 (1280) KiB[19][22]
512 18 80 1440 KiB[19] 300
SHARP X68000 5¼ in high 1024 8 77 2 1232 KiB[19] 360 MFM  
3½ in (90 mm)

Notes and references

  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. http://www.research.ibm.com/journal/rd/255/ibmrd2505ZE.pdf. Retrieved 2008-07-14. 
  3. ^ a b 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)
  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. ^ The Commodore floppy disk format used different numbers of sectors per track in order to store data on wider tracks more efficiently.
  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 The calculated formatted capacity is based on FAT12 format.
  20. ^ While IBM didn't include an 8" floppy drive option on any of their PCs, MS-DOS supported 8" disks and added support for higher capacities in version 2.0. MS-DOS' predecessor 86-DOS used 8" diskettes. [1]
  21. ^ These variations are known as DMF diskettes, used for a time to pack more data on to each disk for software distribution.
  22. ^ a b c d e f Inner 3 tracks of 8 sectors/track format are unused.
  23. ^ 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.