I tried to update 1.2C to 1.2G;
dd if=tk50-file2-12G  of=/dev/ra0d
 then I just  copied boot and netbsd from ra0d to my root partition;
and now it cannot start at all.
After howto=...
it falls in HLT instruction...
What's hell?
Please, help me, if anybody already passed through this trouble....