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Xref: sserve comp.unix.ultrix:24332 comp.unix.bsd:15786 comp.sys.dec:24636 comp.sys.dec.micro:3873 Path: sserve!newshost.anu.edu.au!munnari.oz.au!news.hawaii.edu!ames!haven.umd.edu!news.umbc.edu!eff!news.kei.com!newshost.marcam.com!uunet!topaz.sensor.com!topaz.sensor.com!ron From: ron@topaz.sensor.com (Ron Natalie) Newsgroups: comp.unix.ultrix,comp.unix.bsd,comp.sys.dec,comp.sys.dec.micro Subject: Re: UNIX (Ultrix, BSD?) for DEC Micro PDP-11? Followup-To: comp.unix.ultrix,comp.unix.bsd,comp.sys.dec,comp.sys.dec.micro Date: 21 Dec 1994 19:20:24 GMT Organization: Sensor Systems Lines: 30 Message-ID: <3d9v5o$opt@topaz.sensor.com> References: <taubman.787470030@spot.Colorado.EDU> <arog.787839518@BIX.com> <3d4872$r81@topaz.sensor.com> <3d4r7k$70d@usenet.rpi.edu> NNTP-Posting-Host: localhost.sensor.com X-Newsreader: TIN [version 1.2 PL2] John Wilson (wilsonj@alum01.its.rpi.edu) wrote: : 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 Actually, it doesn't have variable sized pages. It has exactly 8 per address space corresponding to the 8 8K spaces. You just didn't need to point them at a full 8K's worth of memory. : 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 not much worse restartability wise than many other platforms that support UNIX. Ever look at what you have to do with the faulting address register on an i860 after an interrupt? : The PDP-11 is really designed for swapping OSes, not demand-paged ones. Most of the early UNIXes couldn't page either (they were done on the PDP-11). This accounts for the combination swap/page architecture that persists in UNIX today. Even the early ATT and provided VAX (paging architecture) UNIXes, didn't really page. That was Berkeley's contribution. Nope, the real reason you can't do it is because you run out of address space. UNIX programs and the kernel have just gotten too big to run on 64K machines. -Ron