I'm awaiting the delivery of both 1390120 and 1390131 Model Ms, (the M predecessors to 1401), and I am interested to know more about them. I've found many pictures online, but very little background info. I realize the obvious, that the 0120 is a 0131 without lights, they have a metal badge, extra key stabilizers (on numpad + and Enter), and both came with black cords. But I've also read reviews that depict both models as being heavier and more clicky than the later Ms.
Does anyone know what's going on inside of these early Ms that makes them heavier, and if they used a different spring or switch mechanism than the later Ms? What other differences are there, if any, from newer Ms?
(http://www.clickykeyboard.com/2006/1390120/1390120-006.jpg)
1390120
(http://www.clickykeyboard.com/2005/1386085/1386085-001.jpg)
1390131
(http://www.geocities.jp/kenjin_keyboard/1390131p02.jpg) (http://www.geocities.jp/kenjin_keyboard/1390120p05.jpg)
Metal IBM Logo & two extra stabilizer bars on numpad Enter and +