Hello. I tore down a old computer and a PS3. They both had a CPU fan in them. The PS3 fan is a 3-wire,with the brown, black, and grey wires. The one from the computer is also a 3-wire, with the colours brown, black, and grey. If anyone could tell me how to connect it to an Arduino, or a raspberry pi, I would appreciate that. 
Check this link...
Explains the various arrangements. Since this is an arduino forum.... connecting that fan to arduino will likely require extra power supply.... since the arduino won't be able to supply enough power to the fan.
If you don't want to use the third wire for measuring motor speed... then you would just need to use two wires..... the correct pair of wires.