Putting Enough RAM in Your Server
RAM is important for speed in the OS X operating system, and this is particularly true for servers. Server applications can often run faster when you add RAM. More RAM also increases the number of simultaneous client connections that the server can handle without bogging down. On the other hand, filling a Mac Pro with the maximum 64GB of RAM will cost thousands of dollars (if you buy it from Apple), which is a big waste if the server isn’t using it.
The minimum amount of RAM you should consider is 4GB. This amount should provide acceptable results for up to 200 users for light, occasional uses, or for a small network of fewer than 10 computers for file sharing. But keep in mind that the Server configuration of the Mac Pro starts at 8GB of RAM.