1*83 MHz. Multiplier 1 can used by selecting multiplier 2 from the motherboard. And yes, K5 apparently can run Windows 7. For this test I used 83 MHz with 256 MB of ram, but I tried going down to 60 MHz with 128 MB of RAM and it worked too (picture included). Of course it's very slow, to the point where moving the mouse lags, but the fact that it works without any special hacking is a miracle enough.