-HELP- What the FUCK is "Non System Disk"????????

[BIG H]

Need technical support.

I want to install a program on my PC.
As a side note it reads:

*Note: For Vista users, it is recomended to install this program to Non System Disk.


Can anyone explain to me what this means in "dumb ass terms"?
I know a system has several disks but what does it mean by non systen disk?

Non System Disk usually refers to an external Disk, i.e a USB Memory stick. Not sure in this case why it would say to do that? Unless it is a caution to ensure it doesn't corrupt