XP 64!
Ah… was just thinking about memory!
But I do run win7 64 on one of my home computers, of course you need 64bit drivers.
It’s all to do with binary numbers.
a computer said to be “32-bit” also usually allows 32-bit memory addresses; a byte-addressable 32-bit computer can address 2^32 = 4,294,967,296 bytes of memory
Eh…yeah 
A 32bit memory address bus thing, has a limit of the biggest number that 32bit allows, that’s 2 to the power of 32.
Like if it was only 16 bits then it would be 2^16=65536
in theory 64 bit address bus would allow 2^64=18446744073709551616 bytes but there are other considerations to that 
Steve,
If your sound card and any other hardware in your system does’nt have 64bit drivers you’ll have to kiss those goodbye for a start. You may be approaching a time when you may have to seriously consider a major upgrade, unless you can cope with what you have 
.
Having gone through the pains of upgrading to a 64bit system, the extra available RAM, (and the sort of freedom that gives you) is in my opinion is very worthwhile, as always, if you can afford it.
Cheers mate,
Mauri.
Yup… you got it? it’s a physical limit of the 32 bit address bus, there are actually 32 little wires that connect the memory addressing
Win 7 64 does place software limits on the amount of RAM it can see, it’s Microsofts way of making you upgrade to a higher spec 
In actuality, XP can only use 2.5G or thereabouts. It is possible to use a /3GB switch in the BOOT.INI file (in the root of the C:\ drive) but that has no effect unless you are using an application that was specifically designed to support this boot option.
So even if you have 4G of RAM on XP you won’t use all of it.
Allow me to share what I use:
My OS is Win 7 64-bit
I have both Cubase 5 32 AND 64 bit installed… I mostly use 32-bit (out of habit)
I upgraded my Win 7 to Home Premium because it has the XP Mode functionality… so I could use Wavelab 4
most of my VSTi’s have 64-bit versions, with the major exception being UAD, which is under development. However, the UAD (and several other 32-bit VSTi’s I have) run fine using the bridge (either J-bridge or the one that Cubase has)
Hope that sheds some light 
W7 32 can use most 32bit hardware, the problem comes with W7 64, that’s when you need drivers written for the 64 bit OS. You would need W7 64 to be able to see more RAM above the 32bit OS memory limit (although I think JBridge can bridge plugins so each plug can open in it’s own memory window).
JBridge…
“Using inter-process communication mechanisms, it aims to make it possible to run 32bit plugins in 64bit hosts, 64bit plugins in 32bit hosts, or even bridging 32bit plugins to 32bit hosts, allowing to overcome the memory limitations of a single 32bit process, in this last case.”
But why would you want to run a virtual XP 32 in W7 64? just to access memory and or outdated hardware/drivers? You would be using some of the power of a modern system just to host an old OS? leave that to the geeks 
Just to add:
I bumped up the RAM in my Win XP 32 bit to 4GB from 2GB. I now have access to 2.62 GB RAM, because of the limitations above. Believe it or not, that is very helpful - after running Cubase 6.5 with some VSTi’s and audio tracks, etc., I basically had close to 0 MB “Physical Memory” available before, now I’ve got a buffer of more than half a GB more. I’ve noticed my system seems happier since I’ve done that. (I think I probably could have saved $25 and just put 3GB RAM in instead of 4 GB, but that’s a different story).
Also, the 3GB switch is not useless - it just needs the software (e.g., Cubase) to have a flag set so that it responds to it. It tells the computer to allocate 3GB virtual memory to the software and only 1 GB to the OS and other housekeeping functions (“Kernel Mode”), instead of the usual 2 GB/2 GB split. I activated that as well, using 2800 instead of the full 3 GB. I did both of my things at once (more RAM, and this), so I can’t say definitively which (or how much of each) change resulted in my being able to run more VSTi’s, audio tracks.
Here’s a decent review about the 3GB switch in XP, and other RAM issues: RAM Limitations
RAM On!
(“Give your heart to somebody …”)
Like alexis’, my experience with the /3GB was very good in my previous XP 32bit/Cubase 32bit system. The extra 1GB or so of usable RAM made a big difference.
Mind you, it was only a matter of time before all that was’nt cutting it either… .
Cheers,
Mauri.
In my case it allows me to use Wavelab 4 for the price of the Win Home Premium upgrade, which was $89, instead of purchasing a current version of Wavelab, which was about $400 or so
Steve, my recommendation is to go to Win 7 64-bit IF you have a motherboard that will allow you to increase your RAM; otherwise there’s no point. Don’t look at it as “planned obsolesence” – look at it more as being improvements in technology that allow you to work with more power and speed
In my case, going to all 64-bit for over two years now has proved totally worth it – previously I had to use workarounds with bigger projects – not so anymore
Still waiting for 64-bit UAD plugs however –
Hey Steve,
I think one of the things you may well be ‘way behind’ is the power of machines available now. I’m pretty sure you don’t need to wait for that reason !
Going back to when I built my present machine (which is getting old, like me 
), upgrading from a Pentium 4 3GHz to Q6600 overclocked to 3.2GHz, I was blown away by the difference.
Getting a UAD2 Solo and some plugins is helping the machine keep up with the inevitable growth of projects, and need for power, or is it speed…
Being into wires, plugs and stuff, have you built a computer before? It’s great fun and a lot cheaper than a ready made machine.
Cheers,
Mauri.
Another thing which has’nt been mentioned here is that Win7, x86 or x64, will gobble up around 800MB of RAM just idling! That’s about ten times more than my tweaked XP x86, I’m not sure how that affects the amount of usable RAM if you have 4GB.
Mauri.