Slide 4.2: A brief history of hard disks Slide 4.4: A disk access Home

A Hard Disk Structure

---

A single hard disk usually consists of several platters. Each platter requires two read/write heads, one for each side. All the read/write heads are attached to a single access arm so that they can not move independently.

Each platter has the same number of tracks, and a track location that cuts across all platters is called a cylinder.

Each track is divided into sectors. High speed disks have an access time of 28 milliseconds or less, and low-speed disks run 65 milliseconds or more. The higher speed disks also transfer their data faster than the slower speed units.

A hard disk can store anywhere from few gigabytes to more than a few hundred gigabytes, whereas most floppies have a maximum storage capacity of few hundred megabytes.