Memory Management — Basic Principles

Abstract

The allocation of storage to the processes in a time-sharing system poses one of the most major problems to the designer of operating systems. If the system is supporting a large number of user processes, say N, in general it is impractical to keep all of them in memory, as on average only 1/N of the store will be in use at any given instant. Apart from the process that is currently running, some processes will be waiting for a time slice and some (usually the overwhelming majority) will be waiting for a response from the user. This latter category is the most problematic, as the typical response that can be expected from the user might be of the order of a few seconds (but might even be hours). Clearly, the system should not allow such a valuable commodity as its main storage to be underutilised to such an extent.