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Xref: sserve comp.unix.ultrix:24273 comp.unix.bsd:15659 comp.sys.dec:24490 comp.sys.dec.micro:3852 Path: sserve!newshost.anu.edu.au!harbinger.cc.monash.edu.au!bunyip.cc.uq.oz.au!munnari.oz.au!spool.mu.edu!howland.reston.ans.net!news2.near.net!satisfied.elf.com!rpi!wilsonj From: wilsonj@alum01.its.rpi.edu (John Wilson) Newsgroups: comp.unix.ultrix,comp.unix.bsd,comp.sys.dec,comp.sys.dec.micro Subject: Re: UNIX (Ultrix, BSD?) for DEC Micro PDP-11? Date: 19 Dec 1994 20:42:28 GMT Organization: Rensselaer Polytechnic Institute, Troy NY Lines: 17 Message-ID: <3d4r7k$70d@usenet.rpi.edu> References: <taubman.787470030@spot.Colorado.EDU> <arog.787839518@BIX.com> <3d4872$r81@topaz.sensor.com> NNTP-Posting-Host: alum01.its.rpi.edu I haven't looked at the code so I'm on thin ice here, but my impression is that the current crop of UNIX clones is intended to be portable across machines that have fixed-size pages (i.e. no fragmentation, ever) and restartable instructions (for continuing after a page fault). The PDP-11 has variable sized pages -- sure, you could just define them all to be 4KW but then you'd eat through your PDP's tiny memory in no time -- and none but the top of the line machines have restartable instructions (and it's a pain even on them, you need to undo register autoinc/dec by hand using MMR1). The PDP-11 is really designed for swapping OSes, not demand-paged ones. So it would be a very non-trivial port (supposing you found some way to fit the kernel in in the first place) and performance might not be so hot. My impression is that the older unices know about swapping and defragging core and can plan ahead a little more. John Wilson