Your Mac stores certain settings in a special memory area even if it is turned off (unless there is a battery issue as described below). On Intel-based Macs, this is stored in memory known as NVRAM; on PowerPC-based Macs, this is stored in memory known as PRAM. Information stored in NVRAM or PRAM may include: Speaker volume Screen resolution Startup disk selectionYou may need to reset the NVRAM or PRAM if you experience issues related to these functions. For example, if your Mac starts up from a startup disk other than the one you've specified in Startup Disk preferences, or if a "question mark" icon appears briefly when your Mac starts up, resetting NVRAM or PRAM may help.