Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!ucbvax!UOTTAWA.BITNET!451061 From: 451061@UOTTAWA.BITNET (Valentin Pepelea) Newsgroups: comp.sys.amiga.tech Subject: Re: MEMF_PHYSICAL? Message-ID: <8906010252.AA11810@jade.berkeley.edu> Date: 1 Jun 89 02:18:06 GMT Sender: daemon@ucbvax.BERKELEY.EDU Lines: 99 Doug Merritt writes in Message-ID: <360@xdos.UUCP> > In article <8905270516.AA18668@jade.berkeley.edu> 451061@UOTTAWA.BITNET > (Valentin Pepelea) writes: > > > allowed to access each other's memory. The only reason current Minis and > > Mainframes, give tasks their own address space is because two decades ago, > > processors could access only a limited amount of ram. (say 64K) Thus for > > It's sad to see people get confused about such recent history. Your > statement about RAM availability was true for microprocessors and some > mini's but certainly not mainframes (or even all minis). Ridiculous! In the early 70's memory availablity was indeed a concern for mini computers, and in the early 60's it also was for mainframes. I was talking early history, dammit. > And even there, address space limitations has certainly never been > the only reason for giving tasks their own address space. > One of the biggest reasons has always been for protection. It has > generally been considered to be desirable, on say a timesharing system, > to prevent any given process from clobbering some other poor person's > program. Of course protection was a major reason for implementing memory management. But what I was discussing was the memory model, not the protection features. The shortage of ram favorises separate address spaces because it was simpler to just swap out an entire program and swap another one in, than to muck around like we do today. Those were the days of batch environments. Ick. > This is almost true. Unix *once* used that model. Berkeley Unix has > had virtual memory since 1979. Prior to that, on PDP-11's, it > absolutely *had* to swap (no paging support in hardware), so it wasn't > a "poor memory model" at the time, on that hardware. I was talking about early history, and here you come out and talk about 1979. 1979 is Yesterday mister! Anyway, you are just confirming that indeed history is the reason why Unix uses the inefficient superflous memory model. > It's true that AT&T fought tooth and nail to keep VM out of their > versions of Unix, but even they gave up years ago, so both standard > flavors of Unix have had VM for a long time. Longer than the Amiga has > been out. Another confirmation. Not only is Unix brain damaged due to history, but its designers were heavely sedated too! > ... but that's no reason to bad mouth swapping. Swapping is a pain > *only* if you can outdo it, i.e. if you've got demand paged VM. I was not bad-mouthing page swapping. I was bad-mounting the suggestion that we implement separate address spaces, like brain-damaged Unix does. Oh brother! > A) Unix had 4Gig addressing on VAXen in 1979 I was talking about early history, not 1979. The damage was done by the. > B) Exclusively single address space OS's have traditionally been > considered a major *defect* in OS design circles. Again, you are mixing up time-zones. Today, there is only one advantage to having separate address spaces: the ability to layer operating systems on top of each other. That's what virtual machines are all about. Not exactly what an Amiga user whishes to do with his computer. > C) It's true that for some things it's handy to allow shared address > spaces, but only once you first have multiple address spaces. > The fact that the Amiga guru's all the time demonstrates this > quite easily -- crashes are *very* undesirable. Whoa! You are mixing up the "memory model" with "memory protection". The Amiga Gurus very much not because a single address space is shared, but rather because no protection is implemented. That will get fixed very soon. > Shared address space is great in real time systems, but ideally as an > *option*, not the only way to go. Whoa! You are really mixed up! Shared memory is a *requirement* in real-time systems. It is an option is those 'other' brain-damaged systems. Throw that wisky bottle away! > You young whippersnappers think you've got all the answers, but haven't > even done your homework. For shame! Anybody can take my words and twist them around as they please. I am not surprised to see that from a Unix junkie like you. :-) > I like your proverb. > Doug It will be outdated by the end of the summer. Perhaps sooner. Valentin _________________________________________________________________________ "An operating system without Name: Valentin Pepelea virtual memory is an operating Phonet: (613) 231-7476 (New!) system without virtue." Bitnet: 451061@Uottawa.bitnet Usenet: Use cunyvm.cuny.edu gate - Ancient Inca Proverb Planet: 451061@acadvm1.UOttawa.CA