Abstract :
When it comes to computer storage, the magnetic disk has been top dog for almost half a century. The first commercial disks appeared in 1956, and by the early 1970s their cost and capacity had improved to the point where they began to replace magnetic tape as the primary storage medium for computers. By the end of that decade, tapes had been relegated mostly to a backup role. Since then, disk technology has improved at an exponential rate, just like integrated circuits. Nowadays, a typical drive holds 20,000 times as much data as it did in 1985, and on a perbyte basis, disks cost one-millionth of what they did then.
