I need to replace a headset and have a few questions. My only experience has been with traditional ones with ball bearings and races. I see that other than the cheapest ones most now have cartridge bearings. Are cartridge bearings basically the bearings plus races in one sealed unit? Does this mean that there is no wear on the parts fitted to the headtube/fork?

If so how easy is it to get replacement bearings? Are they specific to the manufacturer and model or are they generic and easily available. It sounds great to avoid having to replace headsets because of worn races but if the cartridges aren't available then it is back to square one.

The other issue is the material they are made of. Cheap ones seem to be steel and more expensive ones alloy. My frame is steel. Are there issues fitting an alloy headset to a steel frame similar to the corrosion problems of alloy seatposts in steel frames?

thanks