Shugart Associates first introduced the 5.25-inch form factor along with the first 5.25-inch floppy drive back in 1976. The story goes that Founder Al Shugart then left that company and founded Seagate Technologies, which introduced the first 5.25-inch (Model ST-506, 5MB capacity) hard disk in 1980, predating the IBM PC. IBM later used the Seagate ST-412 (10MB) drive in some of its PC-XT models, which were among the very first PCs to be sold with hard disks built in. The physical format of the 5.25-inch hard disk back then was the same as the 5.25-inch full-height floppy drive, so both would fit the same size bay in a chassis. For example, the original IBM PC and XT models had two 5.25-inch full-height bays that could accept these drives. The first portable systems (such as the original Compaq Portable) used these drives as well. Later, the 5.25-inch form factor was reduced in height by one-half when the appropriately named 5.25-inch half-height floppy drives and hard disks were introduced. This allowed two drives to fit in a bay originally designed for one. The 5.25-inch half-height form factor is still used as the form factor for modern desktop CD-ROM and DVD drives, and is the standard form factor for the larger drive bays in all modern desktop PC chassis. Early portable PCs (such as the IBM Portable PC) used this form factor as well.
Sony introduced the first 3.5-inch floppy drive in 1981, which used a smaller width and depth but the same height as the half-height 5.25-inch form factor. These were called 3.5-inch half-height drives, even though there was no such thing as a "full-height" 3.5-inch drive. Rodime followed with the first 3.5-inch half-height hard disk in 1983. Later 3.5-inch floppy and hard disks would be reduced in height to only 1 inch, which was just under one-third of the original 5.25-inch full-height form factor (these were sometimes called 1/3-height drives). Today, the 1-inch-high version has become the modern industry standard 3.5-inch form factor.
PrairieTek introduced the 2.5-inch form factor in 1988, which proved to be ideal for laptop computers. As laptop sales grew, so did sales of the 2.5-inch drives. Although PrairieTek was the first with that form factor, other drive manufacturers quickly capitalized on the market by also introducing 2.5-inch drives. Finally, in 1994 Conner Peripherals Inc. paid $18 million for PrairieTek's 2.5-inch disk drive technology, and PrairieTek went out of business. Since the 2.5-inch drives first appeared, virtually all laptop systems used them. Although 2.5-inch drives can also be used in desktop systems, the 3.5-inch drive continues to dominate the desktop market due to greater capacity and speed along with lower cost.
The 2.5-inch drives have been manufactured in various thicknesses (or heights), and many laptop systems are restricted as to how thick a drive they will support. Here are the common thicknesses that have been available:
By far the popular sizes are 9.5mm and 12.5mm, which are the sizes used by most laptop. Currently, most drive manufacturers are concentrating on the 9.5mm form factor. A thinner drive can almost always be installed in place of a thicker one; however, most systems will not have the room to accept a thicker drive than they were originally designed to use.
The 1.8-inch drive was first introduced by Integral Peripherals in 1991 and has had problems gaining acceptance in the marketplace ever since. This size was initially created because it fit perfectly in the PC Card (PCMCIA) form factor, making it ideal as add-on removable storage for laptop systems. Unfortunately, the 1.8-inch drive market has been slow to take shape, and in 1998 an investment group called Mobile Storage bought Integral Peripherals 1.8-inch drive technology for $5.5 million, and Integral Peripherals went out of business. Several other companies have introduced 1.8-inch drives over the years, most notably HP, Calluna, Toshiba, and Hitachi. Of those, only Toshiba and Hitachi continue to manufacture drives in that format. HP exited the disk drive market completely in 1996, and Calluna finally ceased operation in 2001. Toshiba introduced its 1.8-inch drives (available in the physical format of a Type II PC-Card) in 2000, and Hitachi entered the 1.8-inch drive market in 2003. The 1.8-inch drives are available in capacities of up to 60GB or more, and depending on the model can be used anywhere a standard PC Card can be plugged in.
During 1998, IBM introduced a 1-inch drive called the MicroDrive, incorporating a single platter about the size of a quarter! Current versions of the MicroDrive can store up to 4GB or more. These drives are in the physical and electrical format of a Type II Compact Flash (CF) card, which means they can be used in almost any device that takes CF cards, including digital cameras, Personal Digital Assistants (PDAs), MP3 players, and anywhere else Compact Flash memory cards can be used. IBM's disk drive division was sold to Hitachi in 2003 and combined with Hitachi's storage technology business as Hitachi Global Storage Technologies.