Installing OS X on Multiple Drives

Hi. I'm trying to run some older software. So I had a Mac dealer install Mac OS X 10.11 (El Capitan) on two separate hard drives in my 2009 Mac Pro tower (I wanted two copies).

In reading the El Capitan Software License Agreement, it kind of makes it sound like there's only one copy of the operating system allowed, for commercial use, per computer. But my use would likely be commercial for both copies.

Are users not allowed to have the same operating system installed, for commercial use, in more than one partition at a time, within the same computer?

I don't imagine that's what it's really saying. But just trying to make sense of the legalese.

Thanks in advance!