Hello everyone, I just had an issue with my new MBPr where an external USB keyboard refused to work on the left USB port. The right USB port was fine, and other devices worked on the left. After some googling, I found PRAM and SMC reset suggestions. I did just the PRAM reset, and hooray everything is working again. With that said, I crave knowledge and knowing exactly what the PRAM and SMC do, why you need to reset them, in what order, and did I take the appropriate steps? Being a PC guy for over 15 years, this troubleshooting is new to me. Any information would be very help! (I'm continuing to search and just can't find any good, complete write-ups on the topic) Thanks!