Secondary Storage Devices

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Secondary storage is the most common storage device, it is any device that stores information permanently and isn't immediately accessible by the processor.

A computer takes much longer to access data stored on a Hard Disk than data stored in RAM.

The computer copies the data or programs needed from the hard disk to RAM, then writes back the to the hard disk when required. If RAM is getting full it will use that hard disk as if it were RAM and the computer appears to slow down.

Hard Disk Drives (HDD)

These store large amounts of data. These are mainly used for storing programs, documents, and anything else that needs to be stored.

External hard drives are becoming increasingly popular as the amount of information that a computer uses is growing rapidly.

Information is held in blocks formed by tracks and sectors. Each block of information contains the same amount; this means that information is more compact and closer to the centre of the disk.

Rotation Speed

A hard disk consist of one or more disks which spin very rapidly in an evacuated housing.

The speed of rotation is such that the reading heads, which are extremely small, are suspended above the disk by the Bernoulli effect, typically about two millionths of a centimetre for a modern hard drive.

The housing is evacuated to prevent specks of dust, or other airborne detritus, from damaging the disk or reading heads, due to the high speeds of rotation.

Capacity