List of floppy disk formats

8-inch, 5 ¹⁄₄-inch, and 3 ¹⁄₂-inch floppy disks

This is a list of different floppy disk formats.

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	250	250	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

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

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 651[3]	8-inch	1972	175	1.5 megabit[4] [unformatted]
IBM 33FD / Shugart 901	8-inch - SSSD	1973	237.25[5][6]	3.1 Mbits unformatted
IBM 43FD / Shugart 850	8-inch - DSSD	1976	500.5[7]	6.2 Mbits unformatted
Shugart SA 400	5¼-inch (35 track)	1976[8]	87.5[9]	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[10]	1200	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[11]	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	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

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

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
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	394 - 590	GCR	[13]
						2	800 KB
		high	512	18	80	2	1440 KB	300	MFM	[14]
Apple Lisa	5¼-inch FileWare	double	512	Variable (15-22)	46	2	851 KB	218 - 320	GCR
Apple Lisa 2/Macintosh XL	3½-inch (90 mm)	double	512	Variable (8-12)	80	1	400 KB	394 - 590	GCR
Apple Macintosh						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	5¼-inch	double	512	11	40	2	440 KB[17]	300	MFM	[18]
		quad			80		880 KB[19]
	3½-inch (90 mm)	double					880 KB
		high		19			1520 KB		GCR	[20]
				22			1760 KB	150	MFM	[18]
IBM 3740	8-inch	single	128	26	73	1	237.25 KB	360	FM	[21]
IBM PC compatibles[22]	8-inch	single	128	26	77	1	250.25 KB[23][24][25][26]	360	MFM	[27]
						2	500.5 KB[23][24][25][26]
		double	1024	8		1	616 KB[23][25][26]
						2	1232 KB[23][24][25][26]
	5¼-inch	double	512	8	40	1	160 KB[23]	300	MFM
						2	320 KB[23]
				9		1	180 KB[23]
						2	360 KB[23]
		quad[28]		8	80	1	320 KB[23]	300
						2	640 KB[23]
		high		15	80	2	1200 KB[23]	360
	3½-inch (90 mm)	double	512	8	80	1	320 KB[23]	300	MFM
				9			360 KB[23]
				8		2	640 KB[23]
				9			720 KB[23]
		high		18			1440 KB[23]
				21			1680 KB[23]			DMF[29]
					82		1720 KB[23]
		extended		36	80		2880 KB[23]
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[23]	360	FM
		double	1024	8	77	2	1232 KB[23]		MFM
	5¼-inch	double	512	8	80	2	640 KB[23]	360	MFM
				9			720 KB[23]
		high		15			1200 KiB[23]
			1024	8	77 (80)[30]		1232 (1280) KB[23][30]			[30]
	3½-inch (90 mm)	double	512	8	80	2	640 KB[23]	360	MFM
				9			720 KB[23]
		high		15			1200 KB[23]			3mode[31][30]
			1024	8	77 (80)[30]		1232 (1280) KB[23][30]
			512	18	80		1440 KB[23]	300
SHARP X68000	5¼-inch	high	1024	8	77	2	1232 KB[23]	360	MFM
	3½-inch (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" (PDF). IBM Journal of Research and Development 25 (5): 701–710. doi:10.1147/rd.255.0701. Retrieved 2008-07-14.
3. Memorex 651 Flexible Disc File OEM Manual
4. Memorex 651 Flexible Disc File - OEM Manual
5. 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."
6. The Evolution of Magnetic Storage, L.D. Stevens, 1981 - "This drive, with a capacity of 243 Kbytes"
7. The IBM Diskette and Diskette Drive, James T. Engh, 1981 - "This would double the capacity to approximately 0.5 megabytes (Mbytes)."
8. 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."
9. 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
10. per 1986 Disk/Trend Report, Flexible Disk Drives
11. Mueller, S: "Upgrading and Repairing PCs", p.656, Que Publishing, 2002.
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), 394RPM to 590RPM
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. This format was used by the Amiga 1020 external floppy drive and some third-party drives connected to the normal Amiga floppy drive bus.
18. 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).
19. Format used by rare third-party drives with quad density disks; such drives were usually switchable between 80-track and 40-track (A1520/PC-compatible) operation.
20. Format used by third-party gcrdisk.device driver in order to use PC-standard HD floppy drives (which rotated at a fixed 300 rpm) via the Amiga floppy drive bus. The Amiga's floppy controller could not keep up with the data rate needed for MFM recording on HD floppies without reducing rotational speed, so the third party driver used an alternate GCR mode.
21. They have 73 data tracks, 1 index track, 2 spare tracks, 1 reserved track
22. Standard Floppy Disk Formats Supported by MS-DOS
23. The calculated formatted capacity is based on FAT12 format.
24. "Standard Floppy Disk Formats Supported by MS-DOS". 2.0. Microsoft Help and Support. 2003-05-12. Retrieved 2012-09-11.
25. Ray Duncan (1988). The MS-DOS Encyclopedia - version 1.0 through 3.2. Microsoft Press. ISBN 1-55615-049-0.
26. Xerox (1983-11). Xerox 16/8 Professional Computer - MS-DOS OS Handbook for 8" Floppy Disks. 1983-11, MS-DOS 2.0 ()
27. 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.
28. Rare format appearing on some early PC/XT clones using quad-density disks.
29. These variations are known as DMF diskettes, used for a time to pack more data on to each disk for software distribution.
30. Inner 3 tracks of 8 sectors/track format are unused.
31. 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.

• The IBM Diskette General Information Manual (PDF). Product Reference Literature (Fifth ed.). IBM. August 1979.
• "RX02 8 inch Floppy Drive Information". David Gesswein. Retrieved 2007-09-21.
• "8 inch floppy disks". University of Amsterdam. Retrieved 19 April 2015.

External links

• Media related to Floppy disk at Wikimedia Commons