Single Address Space Operating Systems (SASOSs) are OSs in which all code and data exists within one, big, shared address space, often threaded. Using one address space facilitates and enhances sharing and cooperation, because it lets addresses have a unique (for all time) representation or interpretation. Thus, pointer-based data structures can be directly communicated and shared between programs at any time, and can be stored directly on secondary storage with no need to translate. Such structures are simplified by using larger address spaces. All earlier OSs were SASOSs, because computers only used single address spaces; that was all that existed, there was nothing else. Segmented/paged address spaces were a later development. Most present, common personal computers use the x86 architecture, which began as the segmented 8088/8086; though i386 and later IA32 processors have a single address space (flat) memory mode. Future, larger processors may return more to single address spaces as the high-end of the computer industry moves to 64-bit CPUs. Or, OSs may keep using processes, which use a different address space for each process. Where SASOSs run as distributed OSs, SASOSs treat a network of nodes as one shared memory machine, using distributed virtual shared memory: DVSM. Some SASOS benefits:
1) Can be made as secure as traditional systems.
2) Are not inherently less efficient than traditional systems.
3) Improve performance over traditional systems on some types of important applications.
4) Give a dual cost advantage: lower initial cost, lower incremental cost.
Part of Computer Science Bibliography Collection of Alf-Christian Achilles.
Orthogonally persistent, capability-based secure SASOS using L4 2nd generation microkernel. Goals: Prove SASOSs can run on normal hardware, be as secure as normal OSs; can be as efficient as, and are faster than, normal OSs in some important uses; can be pure SASOSs with all data (even system data) in one address space and no other IPC mechanism is supported by OS. POSIX emulating. [Open Source, GPL]
Exploring a new OS structure, tuned to the needs of complex applications (eg, CAD/CAM) where a number of cooperating programs manipulate a large shared persistent database of objects.
From Proceedings of the International Conference on Architectural Support for Programming Languages and Operating Systems, Boston, USA, October 1992.
Mail lists, projects, biographies (BibTeX, HTML long, HTML sans abstracts), a few links to other SASOS sites.
Where stale pointers make it hard to re-use addresses, some have claimed that a 64-bit address space is so big that there is no need to ever re-use addresses. Results of kernel-level tracing of department workstations.
Multitasking SASOS with transparent data persistence: users and application programmers need not know or care that system memory is transient and must be written to disk to persist across reboots, all details done by OS, so once data is made, it exists until explicitly destroyed, like physical objects. [Open Source, GPL]
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