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. Single address-space operating systems offer certain 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. 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. SASOS projects include the following: Amiga family – AmigaOS, AROS and MorphOS Angel BareMetal Br1X Genera by Symbolics IBM i (formerly called OS/400) Iguana at NICTA, Australia JX a research Java OS IncludeOS Mungi at NICTA, Australia Nemesis Opal OS-9 Phantom OS RTEMS Scout Singularity Sombrero TempleOS Theseus OS Torsion VxWorks Zephyr See also Exokernel Hybrid kernel Kernel Microkernel Nanokernel Unikernel Flat memory model Virtual memory References Bibliography . Operating systems