A fixed process is a process in which its chunks always reside at the same linear address - their home address; only their access permissions are modified during a context switch.
The usual re-mapping from the data section to the home section is not done and greatly improves performance.
Fixed processes do not see the virtual machine model; each process must have its data at a different linear address. It is, therefore, not possible to run multiple copies of a fixed process.
Fixed processes are suitable only for system server processes such as the file server, window server etc. since the majority of context switches involve these processes.