Which of the following is an appropriate explanation of the characteristics and usage of an optical disk?
Select one:
a. It requires refresh operation at regular intervals in order to retain memory contents.
b. It has three types—read-only, write-once, and rewritable—and is used for storing a large amount of data such as image information.
c. It provides relatively high-speed data access and transmission, and is capable of realizing virtual memory, so it is used in a wide range of equipment from mainframes to PCs.
d. It is not capable of random access but is used for the backup of hard disks because it provides very large storage capacity.