Confused about Prime95 usage

[Winston]

I've been recommended to use Prime95 for testing the stability of my underclocked/undervolted CPU, but there are many different answers to how long I should let it run to be (more or less) sure the system is stabil. I've heard/read everything from 10-15 minutes to 24hours, so I'm a bit confused about it all.

In addition:
Which type of Prime95 test should I run, when it's only the CPU that has been modified?

Can I run other programs while Prime95 is running its tests?

My motherboard/bios does not support reading the CPU core temp from the built-in sensor of the CPU, but uses a sensor placed on the motherboar, underneath the CPU. How many degrees (approx) should I add to this readout to get the actual core temperature?

All help on this is very much appreciated!

 

[OSUmaxx]

You should just run the stress test portion. Make sure to set P95 to use about half of your memory.

I like to run it for at least 12 hours. I don't know about your temp question, but if things get too hot, shut it down

 

[Winston]

How about running other programs at the same time as the Prime95 test? How will this affect the results?

 

[seamadan000]

it won't, if anything it will make the test better, as it stresses the CPU more. However your computer may be a bit sluggish while running prime