Hard disks or magnetic disks have dominated secondary memory since 1965. The term hard is used to distinguish it from a soft, or floppy, disk. A hard disk drive is used to read and write hard disks.
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The figure below shows a top view of the IBM Ultrastar 36ZX [a 36 GB, SCSI (Small Computer Scientific Interface) hard drive] with its top cover removed. Today’s hard drive could easily store several hundred GB of data.
| You can see the hard platters on top of each other with a set of arms which hold the read/write head. The speed of the arm is truly amazing as well as the accuracy of the head which can read and write to perfection on a platter which is rotating around 7,200 RPM (revolutions per minute). |
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