How to Reset PRAM & NVRAM on the MacBook Pro
Apple's MacBook Pro computers feature different types of random access memory than their PC counterparts. While PCs typically use DRAM and SRAM, MacBooks instead feature NVRAM and PRAM. NVRAM and PRAM are non-volatile forms of RAM that maintain their memory state even when they are powered off. If your MacBook is having memory problems, then you can reset its NVRAM and PRAM by rebooting your computer and holding down a collection of keys during boot.
Turn off your MacBook Pro computer.
Prepare to press the "Command," "Option," "P" and "R" keys. You will need to press all four of these keys in unison immediately before your MacBook completes its boot cycle.
Turn on your MacBook Pro.
Press and hold "Command," "Option," "P" and "R." Your MacBook Pro will reset your PRAM and NVRAM, and will restart.
Continuing holding down the keys until you hear the Mac startup sound.