What are a/d d/a converters!?

Yea...I don't really understand what A/d D/a converters are in relation to MPC's... So if I sample into the Mpc from Vinyl...What happens exactlly to the sound? And does the older Mpc's (3000) change the sound with its converters? Oh and are MPC's digital? Or are they analog? Thanks!

oh wow thanks...i read some of it but I will try to read more later...so do diff. MPC's have diff. Converters? Im sure they're not exactlly the same, but do they color the sound greatly? ALso, does Resampling out of the newer MPC's (resamplin the Main OUt) degrade the sound in anyway?Thanks