Was the abbreviation "PC" for "Personal computer" in wide use before the IBM PC?

Solution 1:

In September 1977 (September 19-21, 1977 to be precise) the International Conference on Cybernetics and Society included discussion of the *Personal Computer (PC)". The proceedings of this meeting are not available openly on the internet, but the "Snippet View" from Google Books shows it clearly here:

...personal computer (PC) can then be easily tailored to individual user's needs in his office, at his place of business, or at his home. Our ultimate objective is to make the PC into its user's "intelligent assistant" for real-life situations.

This clearly predates the 1981 release of the IBM PC, although it's not concrete evidence of "widespread" use, as requested by the OP. This document can be found in many University libraries around the world, and if someone has access to a copy, I'd love to know who was promoting the PC in 1977 :-)