Which crystal frequency did they use on the IBM PCs before the AT came out? Kevin. KD5ONS On Sun, 24 Apr 2011 22:09:17 -0700, Rich Heineck <richei at frontier.com> wrote: > 14.318 Mhz has been widely used on PC motherboards going back to the > original IBM PC-AT. > That would be high on my list of suspicious sources. > > 73, > Rich AC7MA