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.