prebuilt-companies: which hard drive is the OS on?

I've never ordered a computer online, and I had this question: When ordering a computer with multiple hard drives, which hard drive do they install the OS to? Is it the smallest or largest by default, or is there some other method (like the "first hard drive" section on the form)?
I'll be ordering from CyberPower in a month or two, and I'm hoping they install to the smaller one because I'm using that hard drive specifically for OS and apps. I e-mailed CyberPower and they have yet to respond, and this was a week ago, so I was wondering if there was a general method or if it's specific per company.

 

From my experience, the manufacturers of these machines are fairly indiscriminate about their installs (I'd imagine that they have an unattended setup) They will install the operating system on whichever drive is designated as the primary master.

 

How's that determined? Is the first hard drive you select (not "hard drive 2") considered a primary master?

 

If they install it that way, yes.