Slide 3.14: Using Unix shell
Slide 4.2: A brief history of hard disks
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Secondary Storage Devices

A secondary storage device is any non-volatile storage medium not directly accessible to the processor. Programs and data stored in secondary storage must first be loaded into main memory before the processor can use them.

Memory directly accessible to the processor includes main memory, cache, and the CPU registers. Secondary storage includes floppy disks, hard disks, optical disks, magnetic tapes, punch cards, and paper tapes.
Unit Size
Byte 8 bits
Kilobyte (KB) 1024 bytes
Megabyte (MB) 1024 KBs
Gigabyte (GB) 1024 MBs
Terabyte (TB) 1024 GBs
Hard Disks
A hard disk is a magnetic disk on which you can store computer data. 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.

The figure on the right shows a top view of the IBM Ultrastar 36ZX (a 36 GB, 10,000 RPM, IBM SCSI server hard disk) with its top cover removed.