Most of the machines in service were older and running OS/2 which was an awesome system. Some major banks (BoA, Chase, WellsFargo, etc.) ran newer machines that had fancier features like check image recognition. Those meant a move to newer OSes but that was a limited case.

The actual reason OS/2 is gone and all these ATMS are running Windows is because of companies like NCR and Diebold lobbying the government to put new language in the Americans with Disabilities Act [1]. It required every ATM to be capable of text-to-speech translation which the older hardware and OS/2 systems were not capable of (most of the machines I was pulling had 133Mhz processors and less than 64MB of RAM). This meant 1) new hardware sales, 2) new software sales, and 3) selling custom ad campaigns to run on the shiny new color screens and new hardware.

The industry had been stagnant for awhile in hardware and software sales, the deadline of March 15, 2012 was a great shot in the arm for NCR and Diebold. Lest you think this really was about helping people with disabilities, the vast majority of ATMs that I 'upgraded' were drive-through units sitting on concrete pallets in bank parking lots too high or too inconveniently placed for anyone to use unless they were driving in a car. I did get some very positive feedback from the blind and their friends(who knew the IRS employs so many blind folk?) when I installed some of the walk-up units, but the large majority were drive-throughs.

[1] - http://www.americanbanker.com/magazine/121_10/atm-accessibil...