Trying to understand PSU rails

PSUs are not really an area I have much knowledge about, so I am attempting to learn a little more about them. I've read the sticky which is really useful and I downloaded MBM to check out my PSU readings. I am a little confused about rails though. For instance if I look at the +5v readout, does this mean I should be seeing it at or around 5v? Because at the moment its showing as being 2.78v? The rest all seem pretty close to their respective ratings. Also, what exactly are the Core 0 and Core 1 readouts?
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More about trying understand rails
  1. The ATX spec says ±5% of the voltage, so it *should* be between +4.75V and +5.25V - MBM gets a bit sensor-confused so double-check by rebooting and seeing the health status in the BIOS to be sure. I think you can re-configure MBM to see the correct sensor if some are flim-flammed. Check the vcore and mem voltages as well and see if they jive w/ MBM. Sometimes your mobo manufacturer's health monitor is more accurate, so it may be worth to install it as well - if for nothing else to compare to MBM...
  2. The ATX spec actually says +/- 10%, but I agree with and use the 5% rule.

    MBM was a good tool - when it was still being updated. It is no longer updated and can give innacurate readings - especially for modern mobos. I don't think his system would remain stable with a 5V rail that far out of spec, therefore I believe that he is getting bad readings.

    I agree that a mobo provided utility is good for monitoring inside windows. Some of the most accurate readings will actually come from the BIOS, but they can be misleading. If you're in the BIOS checking voltages, then you are more than likely not stressing the system and under stress is where you want the PSU to remain stable. Do this to check out your system voltages.

    1. Check your voltages in the BIOS.
    2. Use whatever hardware monitoring utility your mobo mfr provides to check voltages when in windows. Log voltages at close intervals and run a stress test to see voltages while the system is meeting heavy demands. You want to see steady voltages supplied to the rig - large spikes up or down = bad.
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