Quick Intro to Various Types of Memory
The word memory can be used to refer generally
to anywhere we store data for later use, but it is also often used to refer
to one of those types of memory in particular. Here is a quick
introduction to the types of memory that come up in this class:
- Registers: a small number of memory
locations incorporated in the central processing unit (CPU). This
is the closest, fastest memory to the arithmetic logic unit (ALU).
- Memory, often also known as
"main memory" or RAM for Random Access
Memory: the memory being used by currently running processes. It
is close to the CPU, but not as close as the registers. As a
result, accessing data from main memory is much slower than
accessing registers.
- Cache: a small-ish block of memory
that sits between the registers and main memory. A cache is used
to speed up data access from main memory.
- Secondary memory: where programs and
files are stored when not currently being used. Secondary memory
remains stable even when the computer is turned off. Examples
include internal drives, USB drives, etc.
- Virtual memory: blocks of memory
spanning the actual main memory and additional space in secondary
memory. Virtual memory is useful when the currently running
processes need more memory than what the real memory can actually
hold -- in that case some of it is in the actual, physical main
memory and some of it is temporarily stored in a special area of a
hard drive or other type of secondary memory.
Alyce Brady, Kalamazoo College