Single-level storage (SLS) or single-level memory is a computer storage term which has had two meanings. The two meanings are related in that in both, pages of memory may be in primary storage (RAM) or in secondary storage (disk), and that the physical location of a page is unimportant to a process.
The term originally referred to what is now usually called virtual memory, which was introduced in 1962 by the Atlas system at the University of Manchester.[1]
In modern usage, the term usually refers to the organization of a computing system in which there are no files, only persistent objects (sometimes called segments), which are mapped into processes' address spaces (which consist entirely of a collection of mapped objects). The entire storage of the computer is thought of as a single two-dimensional plane of addresses (segment, and address within segment).
The persistent object concept was first introduced by Multics in the mid-1960s, in a project shared by MIT, General Electric and Bell Labs.[2] It also was implemented as virtual memory, with the actual physical implementation including a number of levels of storage types. (Multics, for instance, had three levels originally: main memory, a high-speed drum, and disks.)
IBM holds patents to single-level storage as implemented in the IBM i operating system on IBM Power Systems and its predecessors as far back as the System/38 that was released in 1978.[3][4]
- ^ One-Level Storage System, T. Kilburn, D.B.G. Edwards, M.J. Lanigan, F.H. Sumner, IRE Trans. Electronic Computers April 1962 Accessed 2014-Aug-07
- ^ Virtual Memory, Processes, and Sharing in Multics, Robert C. Daley, Jack B. Dennis Accessed 2014-Aug-07
- ^ Woodie, Alex. "Frank Soltis Discusses A Possible Future for Single-Level Storage". itjungle.com. IT Jungle. Retrieved 4 December 2020.
- ^ IBM System/38 Technical Developments (PDF), December 1978