What are three special purpose devices you might find in a data center and what do they do?

The three special purpose devices one might find in a data center and what they do are : 
1) Load Balancer is a device that acts as a reverse proxy and distributes network or application traffic across a number of. servers.
2) Logical Servers are logically separate servers (e.g., a Web server, an email server, and a file server) on the same physical computer. 
3) Virtual Servers ran on the same physical computer that shares hardware and software resources with other operating systems (OS), they are popular in Web hosting environments.

You probably find kind your i think