You can't be expected to remember every detail about your Macintosh.
Esoteric details like CPU speed, RAM and storage capacity, and what exact version of the operating system aren't exactly the sort of informational tidbits many of us need to track all the time, let alone other information like your Mac's serial number. But these details can be crucial when it comes time to troubleshoot or get help with your Mac. Fortunately OS X makes it really easy for you to find this out. In fact, it's just a couple of clicks away.