Memory

The processor performs all the fundamental computation of the computer system. Other components contribute to the computation by doing such things as storing data or moving data into and out of the processor. But the processor is where the fundamental action takes place.

A processor chip has relatively little memory. It has only enough memory to hold a few instructions of a program and the data they process. Complete programs and data sets are held in memory external to the processor. This memory is of two fundamental types:

• Main memory:
  • closely connected to the processor.
  • stored data are quickly and easily changed.
  • holds the programs and data that the processor is actively working with.
  • interacts with the processor millions of times per second.
  • needs constant electric power to keep its information.

• Secondary memory:
  • connected to main memory through the bus and a controller.
  • stored data are easily changed, but changes are slow compared to main memory.
  • used for long-term storage of programs and data.
  • before data and programs can be used, they must be copied from secondary memory into main memory.
  • does not need electric power to keep its information.

Main memory is sometimes called volatile because it looses its information when power is removed. Secondary memory is usually nonvolatile because it retains its information when power is removed. (However, it needs power when information is stored or retrieved.)