HDDs are connected to systems by standard interface cables such as PATA (Parallel ATA), SATA (Serial ATA), USB or SAS (Serial Attached SCSI) cables. IBM announced HDDs in 1956 as a component of the IBM 305 RAMAC system and as new component to enhance the existing IBM 650 system, a general-purpose mainframe.
The first IBM drive, the 350 RAMAC, was approximately the size of two medium-sized refrigerators and stored five million six-bit characters (3.75 megabytes) and moved in two dimensions, the 1301 was one of the first disk storage units to use an array of heads, one per platter, moving as a single unit.
The 1301 cabinet was about the size of three home refrigerators placed side by side, storing the equivalent of about 21 million eight-bit bytes. Also in 1962, IBM introduced the model 1311 disk drive, which was about the size of a washing machine and stored two million characters on a removable disk pack.
Non-removable HDDs were called "fixed disk" drives.is a data storage device that uses magnetic storage to store and retrieve digital information using one or more rigid rapidly rotating disks (platters) coated with magnetic material.The platters are paired with magnetic heads, usually arranged on a moving actuator arm, which read and write data to the platter surfaces.Some high-performance HDDs were manufactured with one head per track (e.g.IBM 2305 in 1970) so that no time was lost physically moving the heads to a track.