When the power is removed, the memory device (storage media) is considered:
When the data is stored on a volatile device, the data is said to be volatile
Non-volatile / Permanent memory
The data will retain the stored information even if it is not constantly supplied with electric power. It is suitable for long-term storage of information. Nowadays used for most of secondary, tertiary, and off-line storage. In 1950s and 1960s, it was also used for primary storage, in the form of magnetic core memory.
- Disk: used for storing application permanent data
- Read-only memory (ROM) (EPROM, PROM, EEPROM): used for storing firmware such as BIOS
Requires constant power to maintain the stored information. The fastest memory technologies of today are volatile ones (not a universal rule). Since primary storage is required to be very fast, it predominantly uses volatile memory.
- Processor registers – fastest possible access (usually 1 CPU cycle), only hundreds of bytes in size
- Level 1 (L1) cache – often accessed in just a few cycles, usually tens of kilobytes
- Level 2 (L2) cache – higher latency than L1 by 2× to 10×, often 512 KiB or more
- Level 3 (L3) cache – higher latency than L2, often 2048 KiB or more
- the main memory system RAM and controller cards