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Unformatted text preview: so called because they read/write data serially as streams of bits. The
data format used in these tapes has been standardized by the industry and is known as the
QIC standard. This helps in easy use of these tapes for exchanging data between different
computers. That is, data recorded on a streamer tape by one computer can be read by
another computer if both of them use the common QIC standard data format. QIC stands
for Quarter Inch Cartridge. 4mm Digital Audio Tape (DAT)
This is the most recent type of magnetic tape storage device which provides a very high
data density per inch of tape. It uses a tape ribbon of 4mm width enclosed in a cartridge.
The tape length is either 60 meters or 90 meters. Very high data recording density is
obtained by using a tape drive that uses helical scan technique for data recording. As
shown in Figure 8.11, the helical scan has two read heads and two write heads built into a
small wheel (or cylinder) that spins near the tape at about 2000 rpm. At the same time,
the tape also moves past the wheel at a relatively slow speed of about ⅓. inch per second.
The write heads on the spinning wheel each write data with opposite magnetic polarities
on overlapping areas of the tape. Each read head reads only one polarity or the other. The
result is a very high data density per inch of tape. The helical scan records at an angle to
DAT drives use a data recording format called Digital Data Storage (DDS) which
provides three levels of error correcting code to ensure excellent data integrity. Typical
capacity of DAT cartridges varies from 4 GB to 14 GB. DAT drives have a data transfer
speed of about 366 KB/sec.
Advantages and Limitations of Magnetic Tapes
As a secondary storage device, magnetic tapes have the following advantages:
1. Their storage capacity is virtually unlimited because as many tapes as required can
be used for storing very large data sets.
2. With the low cost of tape reels and cartridges and high data recording densities, the
cost per bit of storage is very low for magnetic tapes. An additional cost bene...
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This document was uploaded on 04/07/2014.
- Spring '14