What is this called?

[rdog157h]

My friend used to have 2 towers connected to 1 monitor, could switch back and forth, I want to do the same thing cause I am building a linux system, what is the part that I need called?

 

[Atomic Rooster]

I think you're talking about a KVM switch.

Something like this: Rosewill RKV-2UC 2-Port USB KVM Switch

 

[rdog157h]

Yea that's it, thanks