There is a power-on self test that resides in the ROM of the iMac. This test automatically runs whenever the iMac is powered on after being fully shut down (the power-on self test does not run if the machine is only restarted).
If a problem is detected during the test, you will not hear a normal startup chime. Instead, the system will beep as explained below. Refer to "Error Beeps" later in this chapter for instructions on how to troubleshoot and repair an iMac that sounds error beeps at startup time.
Following is a definition of what the error beeps at startup time signify. One Beep: No RAM is installed or detected.
Two Beeps: Incompatible memory is installed. (The iMac ships with PC-133 SDRAM). Three Beeps: No RAM banks passed memory testing.
Four or Five Beeps: Bad checksum for the remainder of the boot ROM. The ROM is bad.
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