"Darren New" <dne### [at] sanrrcom> wrote in message
news:49b450c9@news.povray.org...
> somebody wrote:

> > Swapping to disk is immaterial of data bus width, it all depends on how
much
> > physical memory you have installed.

> No. It also depends on how much address space you have available to work
> with, if you're talking about OS-supported demand-paged memory.

I meant application managed swapping.

> If you're talking about what Photoshop does, basically building its own
> demand-paged addressing system on top of the application, then no, that
> makes less difference. Photoshop has that feature because it was
originally
> written in the days of 8-bit and 16-bit machines, where it was normal for
> the data to exceed the address space even in usual uses.

Yes, "usual use" is the operative phrase. It's very hard to anticipate what
a "usual use" is, even down 6 months down the road. Adobe got lucky being
forced to make correct decisions at that time. You are also correct that's
it's very difficult to alter the architecture of an existing program, as you
note below. Thus, the safe method is to *not* assume your data will always
fit into physical memory, even if it will fit into the address space for the
foreseeable future. If the possibility is there that the data may not fit
into physical memory, you have to ask if you or the OS will be in a better
position to decide when, if, what and how to page. OS, to me, should be the
last resort. I see entirely too many programs today being written with most
inefficient use of memory since "OS will manage it". With 64 bit address
space, I am pretty sure that we will see applications that are memory hogs
and inefficient at levels we have never seen before.

> Most programs of
> the time had the same kinds of features. It's very difficult to add
> after-the-fact, especially to a program written in a language where it's
> easy to make assumptions about how memory is organized.

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