• One of the important component in the computer system is the computer storage. In this post we will focus on the storage hierarchy.
  • The wide variety of storage system can be organized in hierarchy according to speed and cost. The hierarchy levels are expensive but they are fast.
  • As we move down in a hierarchy the cost for bit generally decrease, where as the access time and storage capacity generally increases.

Storage Hierarchy

  • Semiconductor memory is a faster and chipper type of memory. The top 3 levels of memory in hierarchy is constructed using semiconductor memory.
  • In addition to having differing speed and cost the various storage system are either volatile or non-volatile.
  • Volatile storage lost its contents when the power supply for the device is off.
  • In the absence of expensive battery and generator backup system data must be return to non-volatile storage for permanent storage.
  • In the hierarchy shown in figure the storage system above the electronic disk is volatile where as those below are non-volatile.
  • During normal operation the electronic disk stores data in large D-RAM array, which is volatile. Many electronic disk devices contain a hidden magnetic hard disk and a battery for backup power.
  • If external power is interrupted the electronic disk controller copies the data from RAM to magnetic disk. When external power is restore, the controller copies the data back in to the RAM.
  • The design of computer memory system must balance all this factors.
  • It uses only as much expensive memory as necessary, which providing as much inexpensive, non-volatile memory as possible.
  • Cache can be installing to improve performance where a large access time is needed between two components.