Hard disk drive...

A hard disk drive (HDD), commonly referred to as a hard drive, hard disk, or fixed disk drive, is a non-volatile device which stores digitally encoded data on rapidly rotating platters with magnetic surfaces.Early HDDs had removable media; however, an HDD today is typically a sealed unit (except for a filtered vent hole to equalize air pressure) with fixed media. HDDs (introduced in 1956 as data storage for an IBM accounting computer) were originally developed for use with general purpose computers; see History of hard disk drives.Consequently, hard disk drives can store much more data than floppy disk drives and can access and transmit it faster.As of January 2008: A typical desktop HDD, might store between 120 and 1000 GB of data.The fastest “enterprise” HDDs spin at 10,000 or 15,000 rpm, and can achieve sequential media transfer speeds above 1.6 Gbit/s. and a sustained transfer rate up to 125MBytes/second. Drives running at 10,000 or 15,000 rpm use smaller platters because of air drag and therefore generally have lower capacity than the highest capacity desktop drives. Gamers tend to get 10000 RPM Hard Drives for Gaming PCs due to the fast transfer rate substantially decreasing game load times (and startup times).

Capacity of a hard disk drive is usually quoted in gigabytes and terabytes. Older HDDs quoted their smaller capacities in megabytes, the first drives for PCs being just 5 or 10 MB.The capacity of an HDD can be calculated by multiplying the number of cylinders by the number of heads by the number of sectors by the number of bytes/sector (most commonly 512).Data transfer rate (as of 2008) at the inner zone ranges from 44.2 MB/s to 74.5 MB/s, while the transfer rate at the outer zone ranges from 74.0 MB/s to 111.4 MB/s^] In contrast, the first PC drives could manage only around 40 KiB/s.The technological resources and know-how required for modern drive development and production mean that as of 2007, over 98% of the world's HDDs are manufactured by just a handful of large firms: Seagate (which now owns Maxtor), Western Digital, Samsung, and Hitachi (which owns the former disk manufacturing division of IBM). Fujitsu continues to make mobile- and server-class disks but exited the desktop-class market in 2001. Toshiba is a major manufacturer of 2.5-inch and 1.8-inch notebook disks. ExcelStor is a small HDD manufacturer.