Micro Drive are hard disks (about 1 inch / 25 mm wide) packaged with a CompactFlash Type II form factor and interface. They were developed and released in 1999 by IBM in a 170 megabyte capacity. Then the division was sold to Hitachi in December 2002 along with the Microdrive trademark. There are now other brands that sell Microdrives (such as Seagate, Sony, etc), and, over the years, these have become available in increasingly larger capacities (up to 8 GB as of Oct. 2005).
While these drives fit into any CF II slot, they take more power on average (500mA maximum) than flash memory (100mA maximum) and so may not work n some low-power devices (for example, NEC HPCs). Being a mechanical device they are more sensitive to physical shock and temperature changes than flash memory, though in practice they are very robust.
Micro Drive is a brand name for a miniature 1-inch hard disk designed to fit in a Compact Flash (CF) Type II slot. The release of similar drives by other makers has led to them often being referred to as 'microdrives'. However, 'microdrive' is not a Genericized trademark and manufacturers other than IBM up to 2003 and Hitachi after do not officially refer to these drives as Microdrives. Some other companies, such as Sony, have licensed the name and sell re-branded versions.
These drives fit into any CompactFlash II slot; however, they may take more power than flash memory (up to 500 mA) and therefore may not work in some low-power devices (e.g. handheld computers). Nevertheless, they have some benefits over flash memory in terms of the way data is stored and manipulated. Microdrives which can store 4 GB or more must be formatted for a file system which supports this capacity, such as FAT 32 or NTFS, which may not be supported by older CompactFlash hosts.