Xserve G5 uses DDR400 (PC3200) unbuffered, unregistered ECC (Error Correction Code) memory. Xserve G5 is the first generation of Xserve that uses ECC memory and the Memory tab in Server Monitor now contains ECC-related information.
The version of Server Monitor that comes with Xserve G5 has an additional information field for each of the installed memory cards (DIMMs). This field denotes the number of single-bit (recoverable) ECC errors. If any of the DIMMs in the Memory tab's pop-up menu have a status indicator that is not colored green, this indicates that the DIMM has encountered ECC errors. Single-bit ECC errors are corrected by the ECC circuitry and cause no loss of data or system availability. A summation of the state of all DIMMs is shown in the main status line for a given server.
Server Monitor will also detect multiple-bit errors, but a multiple-bit error will cause a Mac OS X kernel panic. Information will be stored in the Server Monitor logs after the server is restarted. If this happens, you should replace the failing DIMM.
If you see more than four ECC errors in 48 hours, it may be a sign of an impending DIMM failure. Before replacing the DIMM, shut down the server and reseat the DIMM.
Often, a DIMM that is not fully seated will cause failures due to thermal effects on the DIMM connector. If the failures recur, the DIMM is probably about to fail and should be replaced at your earliest convenience.