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From: Walter Roberson on 4 May 2010 13:15
John D'Errico wrote:
> Walter Roberson <roberson(a)hushmail.com> wrote in message
> <pNODn.105596$u62.105086(a)newsfe10.iad>...

>> Now, click on the column for Virtual Memory, again clicking until the
>> triangle points downward. Virtual Memory is the amount of physical
>> memory that your process would use if that memory was available, but
>> it also includes in that total a number of shared libraries that are
>> used by many different programs at the same time, so do not worry so
>> much if you see quite a few programs using 600 Mb or so. However, if
>> you have a process in which the Virtual Memory is larger than your
>> physical memory, then some amount of swapping to disk will be taking
>> place. Swapping of physical memory to disk is something you would
>> prefer to avoid!!

> Walter is describing an operation on a specific (and
> apparently older) version of Mac OSX by the way. He
> really should indicate which version he is describing.
>
> I will point out that the most recent version of OSX
> would be somewhat different.

Walter has been hacking on unix systems for nearly 30 years, and has
never yet met a unix system that did not meet the generic description of
virtual memory and disk swapping quoted above. Certainly it fits the
operation of Mac OS 10.5 (Leopard) on a PowerBook G4 such as Walter has
been running some large processes on over the last 5 months and
observing the performance characteristics.

The one sin of omission Walter made in the generic description was in
failing to account for Demand Page Zero virtual memory, which will not
use physical memory until the first time the page is referenced; such
pages count in the Virtual Memory on unix systems, but it is true that
if the excess of Virtual Memory requirements of a process over the
physical memory that is not pinned down happens to consist entirely of
DPZ memory that never gets referenced, then no swapping to disk would be
necessary. The historical behaviour of Matlab (at least the 32 bit
versions) would suggest that Matlb specifically initializes allocated
memory blocks rather than relying on DPZ zeroing.
From: Kirk on 4 May 2010 14:18

> > Unless you have a wiki:Bastard_Operator_from_Hell running your system,

What is the issue with running a wiki? I am running a couple wikis, and regularly run multi day process is the background. OS X 10.6 seems to allocate memory just fine.
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