If you've built any open source software ever, it's pretty hard not to know of tar, even if you don't know exactly what it is. I think it's reasonable to expect anyone interested in computers would be familiar with common compression tools, let alone a CS major.

> I think it's reasonable to expect anyone interested in computers would be familiar with common compression tools

So 7zip and Winrar?

I joke, but only halfway. If you're only normal Windows user, you'd never hear of anything else (unless you want to go back to Winzip, which does still exist, but I've never heard of anyone using it any more).