What is the noun to refer to the 64- or 32-bit -ness of an operating system

I know that "processor architecture" can be used to refer to whether the processor is 32-bit or 64-bit (or something else), but what word can be used for the operating system? Note that it's not necessarily the same as the processor architecture, e.g. I can install a 32-bit OS on a 64-bit machine.

Also, this is for a business document for non-technical people, so I'd like to avoid an overly technical terminology.

I suggest bitness, in the sense of "The architecture of a computer system in terms of how many bits compose the basic values it can deal with". (Logitech uses it, Microsoft uses it to specify operating-system bitness, et al.)

Word size (e.g. here's a table of word sizes in Wikipedia) or word length.

runs on

A phrase like "runs on 64-bit (32-bit) computers" would make more sense to a lay user.

An alternative, if applicable could be optimized for.

A single word, least a noun, would not suit your audience's reading level.