Multiple BIND instances

[sasa sasa]

Hi,
I got a server with 16GB memory, want to install 2 BIND on CentOS, one cache only and another authoritative.
Is it better to install 2 OS virtually and run BIND in them or run 2 instances of BIND on the same OS? I mean what is the best practice to take advantage of the hardware resources without risking having single DNS with cache and authoritative?

regards,
Sasa