Subj : Re: virtual addresses
To   : comp.programming
From : Ed Prochak
Date : Tue Sep 27 2005 01:06 pm


Brian wrote:
> Randy Howard <randyhoward@fooverizonbar.net> wrote:
> > Bill Cunningham wrote
> > (in article <hs0Ze.922$qC4.180@trnddc02>):
>
> >>     So the applications and the kernel space do not know what the real
> >> physical addresses are then. At least kernel space other than the memory
> >> manager?
>
> > That is typically true for applications (with rare exceptions),
> > but drivers and kernel code often know the physical address or
> > both, depending on what is being done down low.
>
> > If you think about it, there really isn't a reason why an
> > application needs to know the physical address.
>
> > In really high-end systems that support failover and RAID memory
> > systems, and even 'hot add' of memory to a running system, it is
> > extremely advantageous to not have apps tied to physical
> > addresses.
>
> There's one odd thing about virtual memory that is unexplainable.
> Or at least, no one has been able to explain it to me including
> a couple of research guys.
>
> Why haven't we outgrown page files / swap files?  It was an early
> trick and kludge was it not?
>
> My first XP install was on a PIII with 256MB of memory.  I suppose
> the page file was an additional 256MB.  The computer had a practical
> upper memory limit of 512MB.
>
> I have the same version of XP running on a P4 with 2GB of memory
> today.  2GB is approximately 4x my original system's TOTAL available
> memory including it's page file.
>
> In other words, I have plenty o' memory without the disk.  So why
> is the page file still there?

So you think your applications did not grow in the meantime?
(OO bloatware!)

how may windows do you keep open now? How many did you keep open on
your first XP box?

The hardware supports an upper limit of 4Gigabytes of logical memory on
a 32bit address space. So even if your first XP had a practical limit
of only 25% of that, that is per application, so the page file is never
going away.

Never underestimate the power of programmers to consume all the
available memory space.

 Ed

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