[ The PC Guide | Systems and Components Reference Guide | Hard Disk Drives | Hard Disk Geometry and Low-Level Data Structures ]

Hard Disk Geometry Specifications and Translation

The generic term used to refer to the way the disk structures its data into platters, tracks and sectors, is its geometry. In the early days this was a relatively simple concept: the disk had a certain number of heads, tracks per surface, and sectors per track. These were entered into the BIOS set up so the PC knew how to access the drive, and that was basically that.

With newer drives the situation is more complicated. The simplistic limits placed in the older BIOSes have persisted to this day, but the disks themselves have moved on to more complicated ways of storing data, and much larger capacities. The result is that tricks must be employed to ensure compatibility between old BIOS standards and newer hard disks.

Note: These issues relate to IDE/ATA hard disks, not SCSI drives, which use a different addressing methodology.

Next: Physical Geometry

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