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External Memory (Disk Performance (Seek Time (It is the time that it takes…
External Memory
Disk Performance
When the disk is operating it is rotating at constant speed. To read or write the head must be positioned in the right track and the right sector of the track.
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Magnetic Disk
It is a circular platter made with nonmagnetic materials and coated with magnetizable material. Recently this disks are being produced with glass material.
Benefits of using glass as material: Greater ability to withstand shock and damage, increased disk reliability, support lower fly heights, and reduced read-write errors.
CD-ROM
The disk is made from polycarbonate. The information is written with lasers to create microscopic pits on the surface of the polycarbonate. The pitted surface is covered with highly reflective material such as aluminium.
It is used to distribute large amount of data to a large amount of users. This kind of cd can be replicated very easy. It cannot be updated because it is read-only.
Magnetic Tape
Tape systems use the same reading and recording as disk systems. Data is read and written in continuous blocks called physical records. Blocks on the tape are separated by gaps called inter-record gaps.