Do the common arduino boards (aka RAMPS, RUMBA, etc) provide circuitry that facilitate the generation of a PWM signal?

Probably breaks down to two questions:

1. Is there a performance hit on the cpu to generate a PWM signal for the heat pad (apart from some minor math computing the heating values)?
2. In addition to the SSR, do you have to relocate the HB "signal" wiring to a different spot on the controller board that does support PWM, if the current location does not?

Have been googling a bit, and I can't tell for sure if there is any "helper" hardware on the common boards..., or whether the PWM is entirely software implemented...