(Tech Tip: Systems) Common systems and memory configs

Ever wonder what memory goes in your computer? 
Whenever I go to upgrade I never really know which memory to get.
These are the main things to know.

Netiquette Rulebook

Netiquette Rulebook

 Golden rule of Netiquette: don't make people do work for you that you can do yourself.

The rules haven't really changed but the technology we're using sometimes allows us to break them easier and quicker than ever before.  So here's our growing list of the common things you should look out for when trying to be a good corporate netizen.  Any suggestions?