DATA STORAGE - where it is stored o optical compact...

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DATA STORAGE Storage media computers can use several different media for storing information o needed to store both raw data and programs media differ by o storage capacity o speed of access o permanency of storage o mode of access o cost Fixed disks most costly memory next to main/internal memory is fixed disk memory ranges from 10 Megabytes for typical PC to hundreds of Gigabytes in large "disk farms" random access but slower than internal memory permanent (i.e. does not disappear when power is turned off), though data can be erased and modified Dismountable devices dismountable devices can be removed for storage or shipping, include: o floppy diskettes up to 1.44 Megabytes for PC - random access o magnetic tapes tens of Megabytes for standard tape access is sequential, not random can take minutes to reach a particular set of data on the tape, depending on
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Unformatted text preview: where it is stored o optical compact disks (CDs) around 250 Megabytes per CD random access, but the delay in reaching a given item of data may be 1 second or more Volumes • a volume is a single tape, CD, diskette or fixed disk, i.e. a physical unit of storage Files • a file is a logical collection of data - a table, document, program, map • many files can be stored on a single volume • files are given names o the rules for naming files vary among types of systems • the computer operating system keeps track of files stored in a volume by using a table called a directory o files are identified in the directory by name, size, date of creation and often type of contents • files are often organized into subdirectories so that the user can group files under specific topics...
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