Mutability and Accessibility of primary memory:
Read/write storage or mutable storage
It provides permit ion for the information to be overwritten at any time. A computer without some amount of read/write storage for primary storage would be useless for various tasks. Modern computers use read/write storage also for secondary storage.
Read only storage
Receive the information which stored at the time of manufacture, and write once storage (Write Once Read Many) permit the information to be written only once at some point after manufacture. These are known as immutable storage. Immutable storage is utilized for off-line storage and tertiary. For Examples: CD-ROM and CD-R.
Slow write, fast read storage
Read/write storage which permit information to be overwritten multiple times, but along with the write operation being much slower than the read operation? For instance: flash memory and CD-RW
In storage any location may be accessed at any moment in approximately the same amount of time. Such type of characteristic is well suited for primary & secondary storage.
Pieces of information will be accessed of in a serial order, one after the other; so the time to access a specific piece of information depends upon which piece of information was last accessed.
Such characteristic is distinctive of off-line storage.