List of disk drive form factors

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Since the invention of the floppy disk drive, various standardized form factors have been used in computing systems. Standardized form factors and interface allow a variety of peripherals and upgrades thereto with no impact to the physical size of a computer system.

Form factors[edit]

Past and present HDD form factors
Form factor
Status Dimensions
(Each dimension in mm)
Largest capacity Platters (max.) Capacity
per platter (GB)
Length Width Height
3.5 Current 147 101.6 19, 25.4 or 26.1[1] 14 TB[2] (October 2017) 8[3] 1,750[a]
2.5 Current 100 69.85 5,[4] 7, 9.5,[b] 12.5, 15 or 19[5] 5 TB[6] (October 2016) 5[7] 1,000
1.8 Obsolete 78.5[c] 54 5 or 8 320 GB[8] (2009) 2 220[9]
8 Obsolete 362 241.3 117.5 Unknown.
Minimum, 2.0 GB[10][11]
Minimum, 12
Minimum, 0.16
5.25 (FH) Obsolete 203 146 82.6 47 GB[12] (1998) 14 3.36
5.25 (HH) Obsolete 203 146 41.4 19.3 GB[13] (1998) 4[d] 4.83
1.3 Obsolete ? 43 ? 40 GB[14] (2007) 1 40
1 (CFII/ZIF/IDE-Flex) Obsolete ? 42 ? 20 GB (2006) 1 20
0.85 Obsolete 32 24 5 8 GB[15][16] (2004) 1 8
8-, 5.25-, 3.5-, 2.5-, 1.8- and 1-inch HDDs, together with a ruler to show the length of platters and read-write heads
A newer 2.5-inch (63.5 mm) 6,495 MB HDD compared to an older 5.25-inch full-height 110 MB HDD

IBM's first hard drive, the IBM 350, used a stack of fifty 24-inch platters and was of a size comparable to two large refrigerators. In 1962, IBM introduced its model 1311 disk, which used six 14-inch (nominal size) platters in a removable pack and was roughly the size of a washing machine. This became a standard platter size and drive form-factor for many years, used also by other manufacturers. The IBM 2314 used platters of the same size in an eleven-high pack and introduced the "drive in a drawer" layout, although the "drawer" was not the complete drive.

Later drives were designed to fit entirely into a chassis that would mount in a 19-inch rack. Digital's RK05 and RL01 were early examples using single 14-inch platters in removable packs, the entire drive fitting in a 10.5-inch-high rack space (six rack units). In the mid-to-late 1980s the similarly sized Fujitsu Eagle, which used (coincidentally) 10.5-inch platters, was a popular product.

Such large platters were never used with microprocessor-based systems. With increasing sales of microcomputers having built in floppy-disk drives (FDDs), HDDs that would fit to the FDD mountings became desirable. Thus HDD Form factors, initially followed those of 8-inch, 5.25-inch, and 3.5-inch floppy disk drives. Because there were no smaller floppy disk drives, smaller HDD form factors developed from product offerings or industry standards.

9.5 in × 4.624 in × 14.25 in (241.3 mm × 117.5 mm × 362 mm). In 1979, Shugart Associates' SA1000 was the first form factor compatible HDD, having the same dimensions and a compatible interface to the 8" FDD.
5.75 in × 3.25 in × 8 in (146.1 mm × 82.55 mm × 203 mm). This smaller form factor, first used in an HDD by Seagate in 1980, was the same size as full-height 5 14-inch-diameter (130 mm) FDD, 3.25-inches high. This is twice as high as "half height"; i.e., 1.63 in (41.4 mm). Most desktop models of drives for optical 120 mm disks (DVD, CD) use the half height 5¼" dimension, but it fell out of fashion for HDDs. The format was standardized as EIA-741 and co-published as SFF-8501 for disk drives, with other SFF-85xx series standards covering related 5.25 inch devices (optical drives, etc.)[17] The Quantum Bigfoot HDD was the last to use it in the late 1990s, with "low-profile" (≈25 mm) and "ultra-low-profile" (≈20 mm) high versions.
4 in × 1 in × 5.75 in (101.6 mm × 25.4 mm × 146 mm) = 376.77344 cm³. This smaller form factor is similar to that used in an HDD by Rodime in 1983, which was the same size as the "half height" 3½" FDD, i.e., 1.63 inches high. Today, the 1-inch high ("slimline" or "low-profile") version of this form factor is the most popular form used in most desktops. The format was standardized in terms of dimensions and positions of mounting holes as EIA/ECA-740, co-published as SFF-8301.[18]
2.75 in × 0.197–0.75 in × 3.945 in (69.85 mm × 5–19 mm × 100 mm) = 34.925–132.715 cm3. This smaller form factor was introduced by PrairieTek in 1988; there is no corresponding FDD. The 2.5-inch drive format is standardized in the EIA/ECA-720 co-published as SFF-8201; when used with specific connectors, more detailed specifications are SFF-8212 for the 50-pin (ATA laptop) connector, SFF-8223 with the SATA, or SAS connector and SFF-8222 with the SCA-2 connector.[19]
It came to be widely used for HDDs in mobile devices (laptops, music players, etc.) and for solid-state drives (SSDs), by 2008 replacing some 3.5 inch enterprise-class drives. It is also used in the PlayStation 3 and Xbox 360[20] video game consoles.
Drives 9.5 mm high became an unofficial standard for all except the largest-capacity laptop drives (usually having two platters inside); 12.5 mm-high drives, typically with three platters, are used for maximum capacity, but will not fit most laptop computers. Enterprise-class drives can have a height up to 15 mm. Seagate released a 7 mm drive aimed at entry level laptops and high end netbooks in December 2009. Western Digital released on April 23, 2013 a hard drive 5 mm in height specifically aimed at Ultrabooks.[21]
54 mm × 8 mm × 78.5 mm[c] = 33.912 cm³. This form factor, originally introduced by Integral Peripherals in 1993, evolved into the ATA-7 LIF with dimensions as stated. For a time it was increasingly used in digital audio players and subnotebooks, but its popularity decreased to the point where this form factor is increasingly rare and only a small percentage of the overall market.[22] There was an attempt to standardize this format as SFF-8123, but it was cancelled in 2005.[23] SATA revision 2.6 standardized the internal Micro SATA connector and device dimensions.
42.8 mm × 5 mm × 36.4 mm. This form factor was introduced in 1999, as IBM's Microdrive to fit inside a CF Type II slot. Samsung calls the same form factor "1.3 inch" drive in its product literature.
24 mm × 5 mm × 32 mm. Toshiba announced this form factor in January 2004 for use in mobile phones and similar applications, including SD/MMC slot compatible HDDs optimized for video storage on 4G handsets. Toshiba manufactured a 4 GB (MK4001MTD) and an 8 GB (MK8003MTD) version and holds the Guinness World Record for the smallest HDD.

As of 2012, 2.5-inch and 3.5-inch hard disks were the most popular sizes.

By 2009, all manufacturers had discontinued the development of new products for the 1.3-inch, 1-inch and 0.85-inch form factors due to falling prices of flash memory, which has no moving parts.

While these sizes are customarily described by an approximately correct figure in inches, actual sizes have long been specified in millimeters. The older 3.5-inch form factor uses UNC threads, while 2.5-inch drives use metric M3 threads.


  1. ^ 14000/8
  2. ^ Most common
  3. ^ a b This dimension includes a 0.5 mm protrusion of the Micro SATA connector from the device body.
  4. ^ The Quantum Bigfoot TS used a maximum of three platters, other earlier and lower capacity product used up to four platters in a 5.25-inch HH form factor, e.g., Microscience HH1090 circa 1989.


  1. ^ "Ultrastar He12 data sheet - HGST" (PDF). 2016. Retrieved January 18, 2017.
  2. ^ "Western Digital HGST Ultrastar Hs14 Enterprise 14TB Hard Drive Launched". October 2017. Retrieved October 10, 2017. We do not expect many of these drives are going to be purchased from a retailer [..] Larger data centers and systems providers want to manage the SMR process which adds a twist. [..] Host-managed SMR hard drives are designed specifically for sequential write environments, and will not work as drop-in replacements for traditional capacity enterprise drives. [..]
  3. ^ "Western Digital Announces Ultrastar He12 12 TB and 14 TB HDDs". December 2016. Retrieved January 18, 2017.
  4. ^ "Western Digital builds 5mm-thick hybrid hard drive, Ultrabook makers sign on early". Engadget. September 10, 2012. Retrieved January 7, 2013.
  5. ^ "Quantum Go*Drive specifications". Retrieved May 22, 2014.
  6. ^ "Seagate Launches Two New BarraCuda Drives That Pack The Speed, Punch (And Game!) Today's Mobile Warriors Demand". October 10, 2016. Retrieved March 18, 2017.
  7. ^ "Seagate Introduces BarraCuda 2.5" HDDs with Up to 5 TB Capacity". October 21, 2016. Retrieved March 18, 2017.
  8. ^ "Toshiba Storage Solutions – MK3233GSG".
  9. ^ "Toshiba MK2239GSL, 220 GB single-platter HDD" (PDF). Archived from the original (PDF) on 2014-02-23.
  10. ^
  11. ^
  12. ^ Seagate Elite 47, shipped 12/97 per 1998 Disk/Trend Report – Rigid Disk Drives
  13. ^ Quantum Bigfoot TS, shipped 10/98 per 1999 Disk/Trend Report – Rigid Disk Drives
  14. ^ "SDK Starts Shipments of 1.3-Inch PMR-Technology-Based HD Media". January 10, 2008. Archived from the original on March 16, 2009. Retrieved March 13, 2009.
  15. ^ "Proving that 8 GB, 0.85 inch hard disk drive exists". February 17, 2007. Retrieved April 26, 2012.
  16. ^ "Toshiba Enters Guinness World Records Book with the World's Smallest Hard Disk Drive". Toshiba Corp. March 16, 2004. Retrieved September 11, 2012.
  17. ^ "SFF-8500 Specification for Suite of 5.25" Form Factor Specifications" (PDF). SFF Committee. June 5, 1995. Retrieved February 1, 2014.
  18. ^ "SFF-8301 Specification for Form Factor of 3.5" Disk Drives" (PDF). SFF Committee. February 8, 2013. Retrieved February 1, 2014.
  19. ^ "SFF-8201 Specification for Form Factor of 2.5" Disk Drives" (PDF). SFF Committee. October 28, 2013. Retrieved February 1, 2014.
  20. ^ "Xbox 360 HDD Replacement". July 31, 2010. Retrieved March 9, 2016.
  21. ^ Ian Paul (April 23, 2013). "Western Digital rolls out ultra-slim 5 mm Ultrabook drives". PCWorld.
  22. ^ "World HDD Market: Key Research Findings 2010" (PDF). Yano Research Institute. December 15, 2010. Retrieved October 16, 2012.
  23. ^ "Specification for 1.8" (60x70mm) w/Serial Attachment Connector, Rev C" (PDF). SFF Committee. January 2005. Retrieved February 1, 2014.