Subj : Re: virtual addresses To : comp.programming From : Brian Date : Wed Sep 28 2005 05:39 pm Randy Howard wrote: >> Same libraries. Same OS. How does this add up to bigger apps >> exactly? Office still fits on the same ISO cd it did in 1995. > Irrelevant. Binary size != memory consumption, even if it did > matter. Try opening 500 word documents of a few MB in size each > all at once. Good luck. No, that's not normal use, Indeed. >> But I'm seeing 2GB being used quite commonly. Memory has actually >> grown faster than Moore's law. > My memory stays constant in size most of the time, unless I buy > more of it. :-) I have worked on 64GB servers quite a bit, and > you have to work to use it all, but it can be done, from the > command line, with a surprisingly short C program. Real > application developers will start sucking down memory in even > bigger gulps once the 64-bit transition is farther along, you > can count on it. Kind of like Unicode, right? I can't imagine a fetch not being able to distinguish a byte from a long. > Buy what argument? Make a convincing argument that operating > systems shouldn't have virtual memory if that's your position. > So far you haven't done so. I didn't consider diskless systems. It completely slipped my mind (thanks to the other poster for pointing this out). That answers my question precisely. > The debate isn't whether or not > your personal computer has enough RAM or not. It's an example. >>> Either way, virtual memory provides some advantages even in >>> cases where you have more physical memory than your peak usage >>> (which you can't ever guarantee). >> >> So your saying that it's always better to map virtual memory >> to magnetic media versus system memory? I can't see how that >> would ever be true. > I can't see how you came to that conclusion. It's in fact the > last thing I would have expected you to take away from the > discussion. Are you not arguing that disk based virtual memory is required? I thougt you were saying physical RAM will always be too little. If not, I'll have to admit your argument is elusive. The real argument seems to be whether there's any use for a computer that doesn't use the disk as system memory. I contend, as an example, that an XP system with 512MB of memory is useful. With 2048MB of memory, it should be just as useful with an extra 300% memory, plenty to make paging diskless. I can't see the controversy in this at all. >> The entire question boils down to this. What type of memory >> is faster? Is there enough of it? > We definitely are concerned about two different questions, > because I don't think that's even a question worth asking. The > answer has been back on that one for decades. Exactly. So why are we using disks for system memory? >> And I think that, perhaps on a tunable level, system memory is >> plentiful enough to do away with the hard disk. > Hardly. >> The problem is, >> whenever the swap file is eliminated, performance does indeed >> suffer. > Source? None, except for some casual experiments in school. >> The only reasonable explanation is that the virtual memory >> manager degrades at the boundary case - similar to zip compression >> creating a bigger archive file than the raw input. > I don't follow that. If performance /does indeed suffer/ when > the swap file is eliminated, why is an explanation for your > hypothesis that the vmm is having problems? I don't follow. I never said their was a logical problem with any virtual memory manager. I'd expect it works quite well in delivering and securing bytes of data, minus BSODs. :) I said that a virtual memory manager doesn't need the disk. >> That's the part that hasn't been explained to me. I'll dive into >> Linux or OpenSolaris one day and figure it out -- assuming swap >> files aren't eliminated in the meantime. > You do that. I have a working example of a diskless virtual memory manager, so it's a moot point. Hypothesis: Disk paging is necessary . FALSE - proof by counterexample. That may not be accurate enough. There's probably a PIC programmer out there who will balk. Hypothesis: Disk paging is necessary for desktops and workstations. FALSE - proof by counter example. .