Sysctl physmem vs memsize

Question

Hi everyone,
does anyone around here know the exact difference between
sysctl -n hw.physmem
and
sysctl -n hw.memsize
Until recently (about half an hour ago) I was of the opinion that the hw.physmem parameter would give me the amount of physical memory available in the machine. However running it on an 8GB equipped Intel MacPro I get:
sysctl -n hw.physmem
2147483648
which is wrong,
whereas
sysctl -n hw.memsize
8589934592
returns the correct result.
On a G5 Powermac, both versions of the command return the correct result.
Strangely enough, while the manpage
of sysctl itself lists hw.memsize as a valid parameter, it's not listed
on the sysctl.h page where I only find:
HW_PHYSMEM
The bytes of physical memory.
I'm using sysctl in a wrapper script for a Java program where I try to give the JVM as much memory as possible, so if the memsize parameter is the way to go, I'd use that instead of physmem. But if it's some kind of "undocumented" feature I'd rather try to find some other method to check for the physical memory...
Thanks in advance!

Answer 1

I am going to jump on this thread simply because it seems to be a similar though not exactly the same problem I am experiencing.
First, I would also LOVE to find out how to get correct memory sizes from Leopard.
Second, the same method SYSCTL is returning an undocumented value now for the "hw.cpufamily" key on my newer MacBook (the non-pro aluminum unibody from Fall 08) which it reports as 2028621756. This value is not listed anywhere in the documentation on the ADC site so there is no way to properly interpret it beyond saying "Uh, yeah I guess it's a Core Duo 2". =\
Third, it would be wonderful if the "support" at the ADC site actually included regular and timely updates to the documentation about these things or even ways to report errors/omissions. The "support" I received said to come here and ask everyone else which seems more like blowing things off than dealing with them.
Sean.