Memory can be categorized in different ways by technology or
properties: primary access by the CPU or secondary (indirect)
access by the CPU. This distinction is primarily based on the speed
of access to the memory. volatile or non-volatile is a distinction
based on technology (magnetic vs. electrical, etc.). Volatile
memory requires power to maintain its stored information. Read-only
memory, or read-write is a distinction based on properties of the
memory. Read only memory, or "ROM", is not modifiable.