List
| Form factor (inch) | Status | Dimensions (Dimension in inches unless otherwise noted) | Largest capacity | Platters (max.) | Capacity per platter (GB) | ||
|---|---|---|---|---|---|---|---|
| Length | Width | Height | |||||
| 3.5 | Current | 5.75 | 4.0 | 18.28mm, [3] 26.11 mm [4] or 19.99 mm [5] | 32 TB (January 2024) [6] [7] | 11 [8] (October 2024) [9] | 3,200 |
| 2.5 | Current | 4.0 | 2.75 | 5, [10] 7, 9.5, [a] 12.5, 15 or 19 [11] (all mm) | 6 TB [12] [13] [14] [15] (May 2024) | 6 [16] | 1,000 |
| 1.8 | Obsolete | 78.5 mm, [b] 71 mm [c] | 54 mm | 5 mm [17] or 8 mm | 320 GB [18] (2009) | 2 | 220 [19] |
| 1.3 | Obsolete | 50.8 mm, [20] 43 mm [21] | 36.5 mm [20] | 10.5 mm, [20] 5.3 mm [22] | 40 GB [23] [24] [25] (2007) | 1 | 40 |
| 1 (CFII/ZIF/IDE-Flex, "Microdrive") | Obsolete | 42.8 mm | 36.4 mm | 5 mm | 12 GB [26] (2006) | 1 | 12 |
| 0.85 | Obsolete | 32 mm | 24 mm | 5 mm | 8 GB [27] [28] (2004) | 1 | 8 |
| 5.25 (HH) | Obsolete | 8.0 | 5.75 | 1.625 | 19.3 GB [29] (1998) | 4 [d] | 4.83 |
| 5.25 (FH) | Obsolete | 8.0 | 5.75 | 3.25 | 47 GB [30] (1998) | 14 | 3.36 |
| 8 | Obsolete | 14.5 | 9.5 | 4.625 | 2.0 GB (1989) [31] [32] | Unknown (at least 12) | Unknown (at least 0.16) |
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.[ citation needed ] 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.
8-inch
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.
5.25-inch
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+1⁄4-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.) [33] 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.
3.5-inch
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 ("1/3 height," "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. [34] SFF-8301 includes drive heights of 17.80, 26.10, and 42.00mm, but as of 2025, no drives are produced in 42mm height. Drives with heights not mentioned in SFF-8301 are manufactured, e.g. Seagate 19.99-mm-high drives [5] and a Samsung low-profile single-disc drive with a height of 18.288 millimetres (0.72 in). [3]
2.5-inch
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. [35]
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 [36] 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. [37]
1.8-inch
54 mm × 8 mm × 78.5 mm [b] = 33.912 cm³. This form factor, originally introduced by Intégral Peripherals in 1991, evolved into the ATA-7 ZIF with dimensions as stated but with a total length of 71mm. Later, the micro-SATA interface made the total length 78.5mm.
1.8-inch drives with ZIF connectors were used in digital audio players, such as the iPod Classic, and subnotebooks. Later 1.8-inch drives were updated with a micro-SATA connector and up to 320GB of storage (Toshiba MK3233GSG). The 1.8-inch form factor was eventually phased out as SSDs became cheaper and more compact. [38] There was an attempt to standardize this format as SFF-8123, but it was cancelled in 2005. [39] SATA revision 2.6 standardized the internal Micro SATA connector and device dimensions.
1.3-inch
51 mm × 43.8 mm × 10.5 mm. This form factor was used by HP C3013A, C3013B and C3014A, named HP Kittyhawk microdrive, introduced in June 1992.
1-inch
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.
0.85-inch
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.
Modern Usage
As of 2023 [update] , 2.5-inch and 3.5-inch hard disks are 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.[ citation needed ]
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.
