Disk versus Tape
In the past: Both Disks and Tapes were used for secondary storage. Disks were preferred for random access and tape was better for sequential access.
Now (1): Disks have taken over much of secondary storage ==> Because of the decreased cost of disk + memory storage
Now (2): Tapes are used as Tertiary storage (Cheap, fast & easy to stream large files or sets of files between tape and disk)