I think Wilkes got his award for his software contributions despite being well known for his hardware efforts.

The 2009 award to Chuck Thacker, on the other hand, was clearly based on his contributions to hardware. I have the impression that ACM had a change in policy around that time.

But officially I seem to be wrong:

https://amturing.acm.org/bysubject.cfm?cat=16 https://amturing.acm.org/bysubject.cfm?cat=15

In the "hardware" category Wilkes is listed as the only one, while Thacker, with Brooks, Cocke and Wilkes are in the "computer architecture" category.