Here are some very simple guidelines that help determine how much memory a particular server actually needs in order to perform well. Of course, these are just rules of thumb, but nevertheless they might come in handy.
- Database servers (also domain controllers): The database should fit into physical RAM with some to spare.
- File servers: The more, the better. Add RAM until response times under heavy load are a little faster than strictly required.
- Print servers: Not much RAM is needed. 4 GB should be more than enough for typical systems.
- Terminal servers (with or without Citrix): Add RAM until you cannot increase the user density any more without affecting responsiveness.
- Web servers: All frequently accessed content should fit into physical RAM with some to spare.