Chapter 9. Tape Drives
Although the cost and capacity of other removable magnetic storage devices continues to improve, tape drives remain the best choice to back up data or to transfer very large amounts of data between systems. Tape drives provide a combination of high capacity, speed, low media cost, and reliability that no other technology can match. Two tape technologies compete for the standalone PC and small-network market:
- Quarter Inch Cartridge (QIC)
Originally developed in the early 1970s, two styles of QIC cartridges exist. The DC600 is physically larger and is now obsolescent. Recent QIC drives use DC2000 mini-cartridges, which are available in a wide variety of incompatible types and capacities. QIC drives use
serpentine recording, which records many parallel tracks on each tape. The drive records data from the beginning to the end of the first track, reverses direction, writes data from the end to beginning of the second track, and so on, until all tracks have been written. This means that filling a tape may require 50 or more passes of the tape through the drive, which increases wear and tear on both drive and tape. Some recent QIC drives have the extra head required for
read-while-write, which allows the drive to back up and compare data in one pass. Doing a compare on a single-head drive doubles the number of passes required, and extends backup time significantly.
Current QIC drives use Travan technology, a combination of tape and drive technologies developed ...