Lvd: low voltage differential

Hvd: High voltage "

signalling techniques

1) Single-Ended signaling

2) Differential Signaling

Any one using a voltage test instrument can measure charge differential voltage.

when differential signaling was first introduced you could not mix se and hvd devices because of the high voltage used in the hvd. since then a new signaling called lvd is used and it will allow you to use a se if you use the lvd/se mode.( p.1008 managing and maintaining your PC 5th edition)

Yes. The correct voltage is detected based on keying or signaling from the processor.