Hello everyone, I plan to upgrade my old MacBook Pro 13" Mid 2009 running OS X 10.11 El Capitan to 8 GB of RAM (originally 4 GB), and have some question: - The RAM of this machine is old model with 1066 MHz bus speed, and I'm going to install a faster RAM (for instance, 1333 MHz) due to local computer stores don't supply 1066 anymore. Will it work OK for me? I know it's not going to run at full bus speed, but can it harmful anyway? - Will the Apple Hardware Test mode check RAM compatibility? If not, how can I check? If yes, I have problem to enter that mode. I did follow the instruction here, but I couldn't. When I hold down the D key while the machine is starting up, it shows the grey screen for awhile longer before the apple logo appears, after that, it boot to the system normally. So how can I enter Hardware Test mode? Looking forward to your help, Thanks.