I would suggest that you follow the recommended guidelines for local connection: when using FMP13 or FileMaker Go.
RAM: 8 GB
Hard Drive: 80 GB or more, dependent on file size, requires minimum 10 GB free space
If you are using WebDirect: The hardware requirement really depends on how many concurrent connections you are using. see : http://help.filemaker.com/app/answers/detail/a_id/13180/~/system-requirements-for-filemaker-server-13
This page provides recommendations under several scenarios. It would be a good idea to review the FMS13 getting started guide for further clarification.
I hope this helps.