How this works can vary from one BIOS implementation to another, but here is the general case:
You enable an XMP profile and exit from BIOS Setup. The BIOS performs a hard reset of the system. During subsequent POSTs, so long as no issues occur, the BIOS will attempt to initialize the memory subsystem with the settings from this XMP profile. If the BIOS (Memory Reference Code) detects that these settings cannot be supported, it will invoke recovery. Alternatively, if the memory bus(es) hang as a result of these settings, the system will be reawakened by the Watchdog Timer and the recovery code will then be invoked. The recovery code will back off to a safe set of settings (typically 1333MHz for DDR3, 2133MHz for DDR4) and try again. If this is ok, it will come up presenting this "system has POSTed in safe mode" message. At this point,
- If you press F1, BIOS Setup will be invoked and you can choose a different (lower) XMP profile to try. Exiting from BIOS Setup without changing the memory settings will cause the BIOS to continue attempting to use the settings from the selected XMP profile.
- If you press CTRL-ALT-DEL, the BIOS will soft reset and continue attempting to POST using the settings from the selected XMP profile.
- If you presss any other key, the current ("safe") memory settings will be saved into the BIOS Configuration and the system will continue to boot. On subsequent POSTs, the Safe-Mode message will not be seen because the safe mode setting were saved into the BIOS Configuration and they will continue to be used. Bottom line, if you see this message and you continue to boot, it will be operating at this lower ("safe") set of settings on this and all subsequent POSTs.
Hope that helps,
I tried to reproduce this warning but i am not able to do that. Reverting to standard and then again to XMP save. Turn off pc by power button. But not warning. Any ideas why it happened just once,and still its something wrong?
This occured when pc was off some time , 4 hours . And then. I met users using XMP with the same issue , only after pc was off some time.
Memtest not showing errors also.