Hello guys, Im really confused so I need your help.
I have a Mountain bike made in 1998, steel frame, durable and lightweight.Its head is threaded, only thing is that I dont know what is threaded, the old rusty headset, or simply the frame? If the headset is threaded then can I put a threadless headset into it, and fit a fork with 100mm or less (80 is enough too) wich has disk brake mount?Is it a good choice to put disc brakes?Will the fork endure it in a steel frame? Also the head is 1'' sized...

Heres the bike:

If your fork is threaded, you can buy a threaded to threadless adapter allowing you to use modern threadless stems on your bike.

All my bikes have threadless-type stems.