Hi!
It really depends on the workload. If you're just wanting to get familiar with MySQL or need to do some simple testing, you can probably run it any machine that's capable of running one of our supported platforms (see
https://www.mysql.com/support/supportedplatforms/database.html) and has 256 MB RAM to spare. Of course, faster CPU / more cores / more RAM is likely to lead to improved performance.
There's a MySQL Calculator tool (see
http://www.mysqlcalculator.com/) I've heard about that you can maybe use to estimate minimum memory requirements depending on your configuration, but since I've not used it myself, and since this tool is
not hosted or maintained by Oracle, I cannot vouch for its effectiveness or accuracy.
For more specific advice about configuring MySQL and estimating its requirements, you'll need to tell us what you intend to use it for. In particular, MySQL's memory requirements depend on size, number, and design of tables; number of users; types of queries; use of indexes; number of queries per second; and so on.
cheers,
Jon Stephens
MySQL Documentation Team @ Oracle
MySQL Dev Zone
MySQL Server Documentation
Oracle