I know that used to be the case, but understand that since it came along, the Internet is becoming all-too-tempting.
[Edit] It's not the same source I was looking for, but section 7, here:
seems to corroborate that reasonably.
(Certainly better than the 'encyclopedia.com' article I found that asserts that "Inside most ATMs in the early twenty-first century are PCs with an Intel processor chip running IBM's OS/2 Warp operating system." )