Please, does anyone know if the shaft off the engine driven A/C compressor has a 1:1 ratio to engine RPM when ON?

Or, is there a reduction gearing in the connection assembly to the engine, if so, what is the Ratio - ie. if the engine is at 6.5K RPM, what is the A/C compressor RPM?

I have Not, checked my Bentley "Book" - if it is there, and you know, please send me to where...

Thank you

WB