For Opteron, Athlon FX & Athlon 64 , the native 64-bit mode is called "long mode". It allows linear addressing beyond 4GB, unlike 32-bit processors that have to swap in and out (PAE/PSE) the spaces above 4GB.
Microsoft has produced several operating systems for the AMD64 codebase, but none are retailed at the moment.
They all contain the word "for 64-bit Extended Systems"
In a nutshell, Windows XP 64-bit alpha (1023) was sent in December 2002 to some manufacturers, and several pre-release versions were made available to some beta-testers, up to version 1137 recently. Also download of such pre-release AMD64 versions is available for download to MSDN subscribers.
Windows Server 2003 64-bit for extended systems was also pre-released in beta for about 9 months, and just became available for public download, or you can order the CD-ROM (search "64-bit extended" on microsoft.com)
You can retrofit WS2003 to desktop functionaliy if you have problems getting XP 64-bit.
Don't get confused with XP 64-bit for Itanium, which is a whole different processor, and has been available (OEM) for a while
Most of the dual Opteron boards have BIOS upgrades allowing them to run PC3200 with Opterons 242 and above
Whereas a 1GB PC2700 ECC Registered stick will set you back $220, a 2GB is now about $699, and a 4GB PC2100 released by Crucial (at $7000 a piece) could allow your son to upgrade his board to 24 or 32GB depending whether it has 6 or 8 memory slots.
Microsoft certainly did not have a monopoly as far as 64-bit extended systems, since its release to the public in April 2002
Note that the 80386 was released in 1986, and it took about 7 years to see NT retailed.
I feel that 64-bit computing presents tremendous advantages, such as larger RAM disks, and also being able to give separate spaces to leaky 32-bit applications (C++ housekeeping anyone?) under WOW64, and also the fact that virii and trojans might not be so prevalent at the beginning, especially if there is some way NX instruction can work in long mode.
Even though the ECC/Registered memory is 3 times as expensive, it was certainly a bargain to get a dual Opteron motherboard, in relation to smaller Opteron configurations, as the exponential cost of memory far exceeds the difference in motherboard cost ; for instance getting 8GB ECC on a 4-DIMM board would cost about $2800 ($4800 3 months ago) , as opposed to about $2000 on a 8-DIMM board.
Hope this helps,
Chri
