The memory for first and second generation systems is vastly different from the third and four generation onwards. Today, we are in the era of semiconductor memory. There are different kind of memory: the control memory, which is inside the CPU; the cache memory, which is associated with the CPU; the main memory, which is very close to the CPU; the secondary memory including sophisticated disk architecture. Then we have another family of memory system. In addition to hard disk drives and floppy disks, optical disks are used for secondary storage. Optical disks are fast secondary storage devices. Tape systems are slower but earlier predominantly used for archival.

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