f there's an issue with your Mac, it might make one of these tones when it starts up:
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1 beep = No RAM installed/detected
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2 beeps = Incompatible RAM type installed (for example, EDO)
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3 beeps = No RAM banks passed memory testing
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4 beeps = Bad checksum for the remainder of the boot ROM
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5 beeps = Bad checksum for the ROM boot block"
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If there's an issue with your Mac, it might make one of these tones when it starts up:
One tone, repeating every five seconds: No RAM is installed. If you recently replaced or upgraded your computer's RAM, check to see if it was installed properly. If the issue continues, contact Apple Support.
Three successive tones, then a five-second pause (repeating): RAM doesn't pass a data integrity check. If you recently replaced or upgraded your computer's RAM, check to see if it was installed properly. If the issue continues, contact Apple Support.
One long tone while you hold down the power button: An EFI ROM update is in progress. This applies to Mac computers from before 2012.
Three long tones, three short tones, three long tones: EFI ROM corruption is detected, and your Mac is in EFI ROM recovery mode. Newer computers automatically recover from a corrupted ROM; when this occurs, a progress bar appears on the screen during ROM recovery mode. Don't disturb your Mac while the ROM recovery takes place. When recovery is complete, your Mac restarts.
f there's an issue with your Mac, it might make one of these tones when it starts up:
One tone, repeating every five seconds: No RAM is installed. If you recently replaced or upgraded your computer's RAM, check to see if it was installed properly. If the issue continues, contact Apple Support.
Three successive tones, then a five-second pause (repeating): RAM doesn't pass a data integrity check. If you recently replaced or upgraded your computer's RAM, check to see if it was installed properly. If the issue continues, contact Apple Support.
One long tone while you hold down the power button: An EFI ROM update is in progress. This applies to Mac computers from before 2012.
Three long tones, three short tones, three long tones: EFI ROM corruption is detected, and your Mac is in EFI ROM recovery mode. Newer computers automatically recover from a corrupted ROM; when this occurs, a progress bar appears on the screen during ROM recovery mode. Don't disturb your Mac while the ROM recovery takes place. When recovery is complete, your Mac restarts.