Application on Different SQL Servers In a Sql note "you should never put applications in each other's way if you do not have to.. Applications sharing memory, CPUs, internal tempdb  can cause an issue. One application submitting a runaway query can cause server to go to single halt." (SQL Server 2012 Unleashed) (Rankins)

Our company has 5 different applications. None of the multiple applications touch each other or utilize cross database joins. If company budget is not limited, resources are unlimited, and we have small overhead/ample time to administer different servers, should we place all applications on 5 servers boxes?
Unlimited everything?

Sure, buy five different physical boxes at $50,000 each hardware alone, use Core-based Enterprise licensing with SA, patch them all, administer them all, and pay annually for the licensing.

Realistically?  In a way you can justify to accounting?

Use a physical box either directly running Windows and SQL Server, or via a hypervisor, 


give it plenty of RAM (enough to fit your entire DBs if you can afford it) - if you're stuck with Standard Edition, 128GB is the max (leave some for the OS)
a couple good, fast CPU's
and put your data on fast, reliable enterprise solid state drives - either local or on the SAN.
I do agree; do not put your actual applications on your SQL Server system/guest.


If they step on each other, look at the Resource Governor or separate VMs.  Watch out for licensing costs on the latter!