Microdrive
Microdrive is a registered trademark for miniature, 1-inch hard disks produced by IBM and Hitachi.  These rotational media storage devices were designed to fit in CompactFlash (CF) Type II slots. The release of similar drives by other makers led to them often being referred to as "microdrives" too. By 2010, Microdrives were viewed as obsolete, having been overtaken by solid-state flash media in read/write performance, storage capacity, durability, and price.

History
Prior to the 1-inch Microdrive, a 1.3-inch HDD was developed and launched in 1992 by HP with a capacity of 20 MB. These units weighed about 28 g (1 oz), with dimensions of 2.0" × 1.44" × 0.414" (50.8 mm × 36.5 mm × 10.5 mm) and were the physically smallest hard drives in the world before the Microdrive.

In 1999, IBM launched the first generation 1-inch Microdrive with storage capacities of 170 MB and 340 MB.  The physical dimensions of Microdrive were 1.65" × 1.42" × 0.197" (42.0 mm × 36.0 mm × 5.0 mm) and conformed to CompactFlash Type II card standard.  A second generation of Microdrive was announced by IBM in 2000 with increased capacities at 512 MB and 1 GB.  Following the merger of IBM and Hitachi HDD business units, Hitachi Global Storage Technologies continued the development and marketing of the Microdrive.  In 2003, 2 GB and 4 GB models were announced by Hitachi, followed by 6 GB capacity model in 2005.

In 2004, Seagate launched 2.5 and 5 GB hard disk drives in the same small physical form-factor as IBM Microdrive, and referred to them as either 1-inch hard drives or CompactFlash hard drives due to the trademark issue. These drives were also commonly known as the Seagate ST1. In 2005 Seagate launched an 8 GB model. Seagate also sold a standalone consumer product based on these drives with a product known as the Pocket Hard Drive. These devices came in the shape of a hockey puck with an integrated USB 2.0 cable.

In 2003-07-16, a Chinese manufacturer called GS Magicstor, Inc. (subsidiary of GS Magic, Inc.) announced it had produced 1-inch hard disk drive with capacity of 2.4GB at the beginning of the year 2003, originally marketed as an alternative to Microdrive by Hitachi Global Storage Technologies. It was to be followed by 2.2 and 4.8GB 1-inch HDD that was unveiled in 2004 International CES, with 0.8-inch HDD. In 2004-12-28, Hitachi Global Storage Technologies announced it had filed lawsuit against GS Magicstor, Inc., GS Magic, Inc., and Riospring, Inc. for infringement of multiple Hitachi GST's patents relating to hard disk drives, after GS Magic Inc. had started promoting mini-HDD (small form factor hard disk drive).

As of July 2012, there are no known manufacturers of 1-inch form-factor harddisk drives. Hitachi had also stopped production of its trademarked Microdrive product.

Microdrive models by timeline

Date of release of large sizes.

Advantages
 Until 2006, Microdrives had higher capacity than CompactFlash cards.
 Microdrives allow more write cycles, making them suitable for use as swapspace in embedded applications.
 Microdrives might be better at handling power loss in the middle of writing. Flash storage always needs to move some old data around while writing, to ensure the flash's finite write life is consumed equally; if there were a bug in the wear levelling algorithm it could cause data loss if the card were unplugged at the exact wrong time. Data on rotational disks is modified in place, and hard drive algorithms at the time were much more advanced than those of flash storage.
 Microdrives were advertised as weighting less than roll of 35mm film for cameras, while storing thousands of images(for camera of that times). Also at time of use they were sold sometimes with PCMCIA adapter for laptops. Often laptops had then floppy drives so for example 4GB microdrive advert on box show that 4GB microdrive is equivalent of about 2700 floppy disks - 1.44 MB.

Disadvantages
 As of 2006, Microdrive's capacity advantages were exceeded by CompactFlash cards (which are the same size and are often compatible with each other), and USB flash drives. As of 5 July 2015, 512 GB CF cards are available, offering 42 times the storage space of the largest Microdrive.
 Being mechanical devices they are more sensitive to physical shock and temperature changes than flash memory, though in practice they are very robust and manufacturers have added several features to the more recent models to improve reliability. For example, a microdrive will generally not survive a 4-foot (1.2-meter) drop onto a hard surface whereas CF cards can survive much higher falls.
 Microdrives are not as fast as the high-end CompactFlash cards; they generally operate at around 4–6 megabytes per second while high-end CF cards can operate at 45 megabytes per second. This may cause problems for photographers who shoot sequences of large images in rapid succession. Also, they require some time to spin up when they have been idle (see below).
 They are not designed to operate at high altitudes (over 10,000 feet or 3,000 meters), but can be safely used on most commercial aircraft as cabins are generally pressurized.
 Only high capacity models are manufactured, as it is not profitable to make low-capacity Microdrives. At the end of 2005 only capacities above 2 GB are manufactured while 256 MB and 512 MB CompactFlash cards were still in production. Lower capacities are still readily available second hand on eBay but these are usually the same price as CF cards of the same size.
 Unlike flash storage, Microdrives require power even when no data is being transferred to or read from them, just to keep the disk spinning in order to maintain quick access. As a result, many devices such as the iPod mini leave the drive switched off for most of the time while periodically starting it up to fetch data from it to fill the device's buffer. Microdrives will switch off after idling for more than a few seconds to counter this problem; however this means that it needs to spin up for the next access, which takes about 1s. This effect would be particularly problematic if an operating system is being run from the drive, as seen in the case of the Palm LifeDrive.
 Since they are thicker than flash-based CF cards, Microdrives require a Type II slot. Many newer compact cameras only have a Type I slot due to the increasing popularity of flash-based cards, so Microdrives have limited popularity outside of the professional photography market.
 Certain bus-powered CF card readers lack the power needed to run a Microdrive although they do take CF II cards. When using such a device, it will usually be detected by the host but errors will occur once the user attempts to access the drive.
 Some "OEM Only" drives use the CompactFlash form factor but only provide a 5 V IDE/ATA interface. These will not work in readers or devices which expect a 3.3 V interface and full CompactFlash functionality.

Microdrive models by manufacturer

IBM Microdrive
 170 MB
 340 MB
 512 MB
 1 GB
 4 GB
 8 GB
 16 GB

Several physical examples of Microdrives are held by the Computer History Museum.

Hitachi Microdrive
 512 MB
 1 GB
 2 GB
 3 GB
 4 GB
 5 GB
 6 GB
 8 GB
IBM and Hitachi models were fitted with 128 KB of cache memory.

GS Magicstor
 2.2 GB ATA, USB (NATIVE), & CF variants
 3 GB ATA
 4 GB ATA & CF variants
 6 GB

Seagate ST1
 2.5 GB
 4 GB
 5 GB
 6 GB
 8 GB
 12 GB
These Seagate models were fitted with 2 MB of cache memory.

Sony Compact Vault
 2 GB (rebadged Hitachi)
 4 GB (rebadged Hitachi)
 5 GB (rebadged Seagate)
 8 GB (rebadged Seagate)

Toshiba
 2 GB
 4 GB

Cornice
 2 GB
 4 GB
 8 GB

Western Digital
 6 GB

See also
 Digital camera
 Hard disk drive
 HP Kittyhawk microdrive

References

External links
 IBM family of Microdrives - HGST
 Review: IBM's 1GB Microdrive – review on MP3 Newswire
 Hitachi Global Storage Technologies (HGST)
 Review of Seagate ST1 5 GB 1-inch hard disk for CF

Hard disk drives
Divested IBM products
Hitachi
IBM storage devices
Computer-related introductions in 1999