Fixed Space Vs. Variable Space
In a multiprogramming system, we need a way to allocate memory to the competing processes.
- Question is: how to determine how much memory to give to each process?
In a fixed-space algorithm each process is given a limit of pages it can use; when it reaches its limit, it starts replacing new faults with its own pages. This is called local replacement.
- some processes may do well while others suffer.
In variable-spaced algorithms, each process can grow or shrink dynamically, displacing other process’ pages. This is global replacement.
- one process can ruin it for the rest.