When this occurs, a progress bar appears on the screen during ROM recovery mode. Newer models recover automatically from a corrupted ROM. This means that your computer has detected an EFI ROM corruption and the computer is in EFI ROM recovery mode. This only happens on computers manufactured before 2012. This indicates that an EFI ROM update is in progress.
1 long tone if you hold down the power button:.This indicates that the Mac found RAM installed, but the memory failed to pass the data integrity check. 3 successive tones followed by a 5-second pause:.Either your computer's memory was removed or something is interfering with the system checkup. If you hear this pattern of beeping, it means that the Mac could not find any RAM installed. When you start your Mac, it will automatically run system diagnostics. Here’s a short list of what each beeping pattern means: Sometimes you'll turn your Mac on and it'll start beeping in a variety of patterns.
