Patches?

[Imp]

Vesku is indeed correct for optimum speed backup & security operating system on C thats it nothing else. Then if like put programs in say D & data in E.
You can now quickly virusscan or backup seperate drives (or partitions) or like work computers tend to be set up hide a drive/partition.
Can also assign your page file to the drive that gets minimal use for speed.
This way backing up C & data means you just reinstall programs if it goes belly up.
With Vista on you are far better putting programs anywhere but the programs folder, never ever install a game there due to microsofts meddling.

Walrus wrote
I guess the logic is that the Apps need to talk to the OS all the time and it's easier / faster if they are on the same drive.

If both applications have to access the drive its slower 2 reads off 1 drive. Seperate drives reading one off each so its marginaly quicker dependant on where page file is of course.