Single address space operating system

In computer science, a single address space operating system (or SASOS) is an operating system that provides only one globally shared address space for all processes.

In a single address space operating system, numerically identical (virtual memory) logical addresses in different processes all refer to exactly the same byte of data.[1]

Single address-space operating systems offer many advantages. In a traditional OS with private per-process address space, memory protection is based on address space boundaries ("address space isolation"). Single address-space operating systems use a different approach for memory protection that is just as strong.[2][3]

One advantage is that the same virtual-to-physical map page table can be used with every process (and in some SASOS, the kernel as well). This makes context switches on a SASOS faster than on operating systems that must change the page table and flush the TLB caches on every context switch.