The Minolta XG-M was introduced in 1981, short before the X-700. It was the first to show the 'X-designed body', although technology inside was based upon the 1970's XG-series. The X-700 that followed a few months later was much more sophisticated.
This is the only XG with full active light meter when used manual. DOF-button is still in metal, like the XG9 and XD's. The X-500, which followed two years later, almost looks identical. The XG-M is heavier,though and -of course- the X-500 is better equipped and more a 1980's-camera. Still, the XG-M is a good tool to take wonderful pics, certainly when Rokkor glass is used. XG-M bodies sell for almost nothing these days.