Lenovo Is6xm Rev 1.0 Motherboard Manual | Fresh

You can find the detailed layout, including front panel pinouts and jumper settings, in the ThinkCentre M81, M91, and M91p Hardware Maintenance Manual provided by Lenovo Support Header/Port Description Standard 24-pin ATX and 4-pin CPU power. Front Panel Proprietary 13-pin (2x7, one pin missing) Lenovo header. Note: Standard ATX cases may require an adapter.

The IS6XM uses several proprietary Lenovo headers that can be tricky for users migrating the board to a standard retail case. Lenovo Is6xm Rev 1.0 Motherboard Manual

It wasn't a manual. It was a map.