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Table of 8-inch floppy formats

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Table of 8-inch floppy formats


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) 33.333 250 250 250 500 500 500 500 500
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

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

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 79.75 ?
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 360 ?
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 720 ?
Mitsumi Quick Disk 3-inch 1985 128 to 256 ?
2-inch 1985 720 ?
5¼-inch Perpendicular 1986 100 MiB ?
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 MiB 120 MB
LS-240 3½-inch 1997 240.75 MiB 240 MB
HiFD 3½-inch 1998/99 150/200 MiB 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 220. 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 KB 360 FM [11]
Acorn 5¼ in 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 in (90 mm) double 256 16 80 2 640 KB 300 MFM
1024 5 800 KB
high 10 1600 KB
Apple II 5¼ in double 256 13 35 1 113.75 KB 300 GCR [12]
2 227.50 KB
16 1 140 KB
2 280 KB
3½ in (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 Macintosh 3½ in (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 in single 128 18 40 1 90 KB 288 FM [15]
enhanced 128 26 127 KB MFM
double 256 18 180 KB
Commodore (8-bit) 5¼ in 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 in (90 mm) double 512 10 80 2 800 KB MFM  
Commodore Amiga 3½ in (90 mm) double 512 11 80 2 880 KB 300 MFM [17]
high 22 1760 KB 150
IBM PC compatibles[18] 8 in 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 in 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 in (90 mm) double 512 8 80 1 320 KB[19] 300 MFM
2 640 KB[19]
9 720 KB[19]
high 18 80 1440 KB[19]
21 80 1680 KB[19] DMF[24]
82 1720 KB[19]
extended 36 80 2880 KB[19]
NEC PC98 8 in single 128 26 77 1 250.25 KB[19] 360 FM  
double 1024 8 77 2 1232 KB[19] MFM
5¼ in 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 in (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 in high 1024 8 77 2 1232 KB[19] 360 MFM  
3½ in (90 mm)

Notes and references

External links

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