I. Secondary Memory
In the previous lecture, we saw that RAM is expensive and has a limited storage
capacity. Since it is a volatile memory, it cannot retain information after the computer
is powered off. Thus, in addition to primary memory, an auxiliary or secondary
memory is required by a computer. The secondary memory is also called the storage
device of computer. In this lecture, the terms secondary memory and storage device
are used interchangeably. In comparison to the primary memory, the secondary
memory stores much larger amounts of data and information (for example, an entire
software program) for extended periods of time. The data and instructions stored in
secondary memory must be fetched into RAM before processing is done by CPU.
Magnetic tape drives, magnetic disk drives, optical disk drives are the different types
of storage devices.
II. MAGNETIC TAPE
Magnetic tape is a plastic tape with magnetic coating (Figure 5.1). It is a storage
medium on a large open reel or in a smaller cartridge or cassette (like a music
cassette). Magnetic tapes are cheaper storage media. They are durable, can be written,
erased, and re-written. Magnetic tapes are sequential access devices, which mean that
the tape needs to rewind or move forward to the location where the requested data is
positioned in the magnetic tape. Due to their sequential nature, magnetic tapes are not
suitable for data files that need to be revised or updated often.
They are generally used to store back-up data that is not frequently used or to transfer
data from one system to other.
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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