Past exam of the mathematics course of the University of Cambridge / 2007 / ia / Paper 5 / 2 / b / Solution

Both kinds of context switch save and restore registers, a program counter, stack pointer and scheduler state. Switching between operating-system processes additionally changes the address-space and protection context, including the page-table root. Cached translations must be invalidated or distinguished by address-space identifiers, and the new process may have a different memory and cache locality.

Software threads of one process share its address space and most resources, so a thread switch normally preserves the page-table root and valid cached translations; only the execution context, stack and thread-specific state need change. Thus a process switch requires address-space management which a same-process thread switch usually avoids. Tagged translation caches can reduce the extra cost, so a complete translation lookaside buffer flush is not an inevitable feature of every process switch.