[geeks] Windows XP 64bit Licensing?

[Mike Meredith]

On Wed, 27 Jun 2007 15:25:34 -0400 (EDT), nate at portents.com wrote:
> > All memory in Linux is virtual addresses and any given physical
> > address can be marked off limits for paging VM.
> 
> Really.  Then explain this:
> 
> http://ubuntuforums.org/showthread.php?t=484222

It's wrong (except for the mention of a 'patch' ... really an option
when compiling the kernel). It presents the common misunderstanding
about the difference between the 32-bit address space a *process* can
see and the larger address space the MMU can see.

Let me re-phrase that ... Linux (assuming it has the relevant switch
turned on) can see *all* the memory in a system, and will map a
process's address space to maximally utilise it's 32-bit limit. People
see that processes are limited to a 32-bit address space and assume the
system is similarly limited.

The 32-bit limit (giving 3G for user-space/1G kernel space, or on
really old versions of Linux, 2G/2G) is a problem for large monolithic
server processes like Oracle (or sometimes applications like
Photoshop/GIMP), but it isn't usually too much of a problem on a
workstation ... yet.

As an example, I have a server with 16Gbytes of memory running a 32-bit
os :-

% cat /proc/meminfo | grep MemTotal
MemTotal:     16570024 kB
% uname -a
Linux kiev 2.6.5-7.283-bigsmp #1 SMP Wed Nov 29 16:55:53 UTC 2006 i686
athlon i386 GNU/Linux 
% file /bin/ls
/bin/ls: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), for
GNU/Linux 2.2.5, dynamically linked (uses shared libs), not stripped

Now it may be that Ubuntu doesn't automatically load the 'bigsmp'
kernel (or whatever Ubuntu may term it), but that's a Ubuntu problem
and not a Linux problem.

> And yes, there are ways around it with memory extentions such as
> 36-bit PAE, which has it's own unique set of limitations and
> restrictions, here's how you'd set up PAE in 32-bit Linux for Oracle:
> 
> http://www.oracle-base.com/articles/linux/LargeSGAOnLinux.php

No, that's not how you setup PAE in 32-bit Linux; it's an old set of
instructions (RedHat AS2.1??) on how to use the shared memory
filesystem as a way around the 3G/1G limit for Oracle. You'll note it
specifically mentions that the shared memory filesystem can utilise all
memory recognised by the system.

The PAE stuff is commonly referred to as a memory extension ... from a
system administrators point of view, it isn't. It's an MMU that can
address more memory than a process can see. 

-- 
Mike Meredith (http://zonky.org/)
  "Spammers on the Internet are like hula hoops, pet rocks, or subway
   alligators; only incredibly fertile, incontinent, and able to fly.
And it's still illegal to shoot them, so bring an umbrella." SC, on
SPAM-L.