Digital audio tape is a type of magnetic tape that uses a same technology as helical scan to record data. A data cartridge is slightly larger than a credit card in width and height and contains a magnetic tape that can hold from 2 to 24 gb of data. it can support data transfer rate of about 2 mbps. Like other types, data are sequential access media.
Hard disks are used for on line secondary storage device for most computer systems today. The introduction of high capacity disks for microcomputer systems solved two problems related to the limited storage capacity of diskettes.
First as a business began to use microcomputers extensively the amount of software acquired and data collected grew up substantially. Now a day hard disks having capacity of several gb is available. So storage of huge amount of data is no problem.
Secondary the largest file that could be accessed at one time was limited to the capacity of main memory and the storage medium. Since the capacity of hard disk is virtually unlimited, there is not constraint of accessing to any length of file.
Data is stored in the same way as it on diskettes. A series of tracks are divided into sectors when the disk is formatted. As their name suggests, hard disks are made out of a rigid substance that is capable of storing a greater amount of data than the soft material used for diskettes. Hard disk drivers for microcomputer can be internal (built into the computer cabinet)or external (outside the computer cabinet and connected to it by a short cable).
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