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Aucbvax.4736 fa.unix-wizards utzoo!decvax!ucbvax!unix-wizards Tue Oct 27 22:33:53 1981

>From obrien@RAND-UNIX Tue Oct 27 21:46:34 1981 The general feeling is that the 11 has too few paging registers to make a paging scheme worthwhile on this architecture. Also, except on 70's, you don't have I/O paging hardware available, so swapping scattered pieces of a process is hard and raw I/O becomes impossible. One or two people actually built, or tried to build, a paging PDP-11 UNIX, but either gave it up or it never caught on.

Things like VAXen are a different story. There, while the text/data/bss trichotomy has been retained at the user level, in fact things are done in discreet pages and swapped that way. UNIX/32V does "scatter/gather" swapping, where a process can be scattered throughout memory but must be all in-core to run (i.e. no page faults allowed), so it looks like the kind of UNIX you have in mind. Given the notion of enough page registers, though, and enough I/O paging hardware as well, the continuation to the Berkeley VMUNIX fully paged system is natural enough. Paging to a solid-state device would be wonderful and I wonder why no one's tried it.

DEC OS's, I believe, are worse than UNIX. They've only recently started supporting split I/D on 11's.

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