Dennis, Colin's original statement was right, it is mathematically
impossible to address more using 32 bits. It is possible using 32 bits
AND something else to physically achieve what "Looks like" addressing
more but this is by ADDING something - the limit is real if nothing
extra is added.

The Commodore 64 really had 64K, but also a 32K ROM BASIC and a IIRC 2K
which today we might call an OS or BIOS.

64K WAS the physical limit, but the ROM overlaid it and could be turned
off, which we did all the time to load games. I personally wrote
software that could both use the BASIC and page it our for storage, then
back in again for use. But I could NOT use BASIC routines and the
underlying RAM at the same time.

So I think we are down to semantics here where nobody is actually
"Wrong" but disagree about descriptions. I never owned a 96K Commodore
but was able to use more than 64K.

Note Colin's mention somewhere here of a "Performance Hit", that is why.


dennis wrote:
It is a nice story, but still not what we are talking about. We are
talking about what is technically possible. And the fact is, you can
address more than 4GB in PAE mode. Microsoft just choose not to do so in
XP/SP2 and Vista.

Colin Barnhorst wrote:
If you want to argue that PAE is treated as a value-added item and
therefore Marketing decided to "withhold" some of its functionality
from Windows clients for price differentiation purposes, go ahead.
They do that stuff all the time. That's why the Snipping Tool isn't
in Vista Home Basic. However I personally don't think there was
anything like that decision making involved with PAE.

PAE showed up around 8 years ago, if I remember correctly. Think back
to what Windows client computers were back then. A typical consumer
box at Best Buy or Comp USA was going out the door with WinME and
128mb of ram with mobos whose memory controllers were limited to 512mb
of ram. The hardware simply didn't support any more. DDR hadn't even
shown up.

By late 2001 machines were being sold with XP Home and 256mb of ram.
It cost the buyer a couple of hundred bucks to upgrade to 512mb and
mobos with three memory slots did not support anything more than
768mb. The four-slot ones could support 2GB but 512mb memory sticks
were horribly expensive and machines usually sold with 256mb (two
sticks). A few folks added more.

While all this was going on Enterprise class server boxes that could
support 4+GB cost between $10k and $20k. The push for 4+GB was coming
from medium and large enterprises with large SQL and Exchange loads.
Enter PAE (there were other schemes as well). MS was not solving a
general problem with PAE. They were addressing a need expressed by
enterprise users. So they developed Windows 2000 Advanced Server and
all later Enterprise server editions to enable PAE if needed. There
wasn't a need to address the issue on the client side. So why would
they?

When Intel developed the data execution bit for the later Pentium 4s
in order to support DEP it turned out that PAE could also address a
conflict sometimes encountered with DEP. That's when MS wrote PAE
support into the service packs that were releasing for W2k and XP.
But only to address the problem. Folks weren't running desktops with
4GB of memory at that time, much less ones with more than 4GB.
However, workstation users were and that's when MS wrote XP Pro x64 to
address that memory need. I don't think MS has ever considered PAE as
a suitable solution for consumers and workstation users in addressing
memory needs. There can be a perf hit with it and I think the
judgement to provide 64bit consumer operating systems like Vista was
the better choice.