Nonvolatile and Volatile Memory
There are two major classes of computer memory: nonvolatile and volatile. Nonvolatile memory is retained even if the power is shut off. The setup data held in CMOS, discussed in the preceding lessons, is a good example of nonvolatile memory. If the data is lost when the computer loses power, the memory is said to be volatile.
Active memory is a state in which a block of code or data is directly accessible to the CPU for reference or manipulation. When data is located outside the system's active memory, it is said to be "in storage." Storage devices include floppy disk and hard disk drives, optical media, and tape units.
Active memory is faster than storage because the information is already on the system, there are fewer physical (and no mechanical) operations involved in obtaining the data, and the CPU has direct control over the memory.