CS3 Preferences/Performance not recognizing full amount of memory

Question

I have increased RAM in a Windows XP Pro, 32bit PC, from 2 GB, to 4 GB.  Windows recognizes that I have 3,141,872 kb of physical memory available.  Yet, Photoshop CS3 only shows available RAM of 1705 MB (Edit-Preferences-Performance-Memory Usage).
I am preparing to do Boot.ini modifications to the /3GB, and /userva switches to increase RAM available to PS.  I assumed that PS would show an increase in available RAM, even before modifying the switches.
I've been assured by a knowledgeable Windows/PS user that these mods are straight forward.  Yet, when I told him that PS was not recognizing the new Ram, while Windows XP was recognizing it, he suggested I post this on the Adobe PS forum.
Hence, my thread.   In sum - why doesn't PS recognize the new amount of RAM, or how badly have I misunderstood the concept?  (It's probably operator error.)

Answer 1

CS3 will recognize ~1GB more of your RAM after you edit your boot.ini file to invoke the /3GB switch, not before. Without going into all the reasons why this is so, just bear in mind that the /3GB switch is not risk-free; a minority of computers will not boot at all (in normal, safe or any other mode) once it's enabled. Make sure you have a viable exit/recovery strategy in case that happens to you. Also remember that there is no free lunch even if the switch works without a seeming hitch. In order to give that RAM to Photoshop, you have to take it from Windows. The UserVA that you mentioned helps to mitigate the effects of that theft somewhat. Know also that you can edit the boot.ini to give you the option of running with or without the switch enabled. This is accomplished by means of a menu during boot up. It's also a legitimate recovery option in the event your computer and the switch can't coexist.
I use the switch, but ONLY when I expect to do a lot of heavy lifting in Photoshop. I shut down as many superfluous background apps as I can, including anti-virus and  my firewall. In other words, I don't push my luck by taxing the OS when running with the switch enabled. I would specifically not recommend using it for an everyday computing environment.
I suggest you read a little more before you make the move.
EDIT: Here's my boot.ini. DO NOT USE IT unless your disk and partition assignments are the same. I am posting this so you can see how to give yourself the option of selecting a config with or without the switch at boot time.
[boot loader]
timeout=5
default=multi(0)disk(0)rdisk(0)partition(1)\WINDOWS
[operating systems]
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows XP Professional Baseline" /noexecute=optin /fastdetect
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows XP Professional 3GB" /3GB /Userva=2900 /noexecute=optin /fastdetect