How do modern dSLR cameras synchronise their flash up to 1/500 second?

With focal plane shutters on SLR cameras it used to be that the whole of the frame had to be uncovered at one time when using electronic flash. From my research before purchasing a new camera I see that the Nikon D50 will synchronise at up to 1/500 and Olympus suggest their SLRs synchronise at all speeds. Can anyone tell me how this is achieved.