Since the 1950s, tape has persisted as the media of choice when inexpensive and reliable data storage is required. The roles played by tape include data interchange, processing, and storage; today tape serves generally as a media for archiving and backup. Progress in tape technology has resulted from substantial advances in channel, head, drive, and tape. Moreover, the cost of tape storage, normalized per unit capacity (dollars per gigabyte), has decreased steadily over time driven primarily by advances in areal density and reduction in tape thickness.
Areal density is a two-dimensional measurement obtained as the product of linear density and track density. Linear density is a measure of how tightly bits are packed longitudinally along a length of tape. Increases in linear density tend to lead to an increase in intersymbol-interference (ISI), unless corrected. Track density is a measure of how tightly tracks are packed laterally on the tape. Increases in track density implies narrower track width, narrower write/read heads, and closer head spacing, all of which tend to lead to losses in signal-to-noise ratio (SNR), unless corrected. Increasing linear densities beyond those achieved by state-of-the-art tape systems is becoming difficult. Improving track density may therefore provide further improvements in areal density.