As Michael Petrotta mentioned it is the Personal System/2 from IBM which defined the new "Standard" as a time when proprietary connections were the standard.
IBM introduced a new keyboard with each of its major desktop computer
models. The original IBM PC, and later the IBM XT, used what we call
the "XT keyboard." These are obsolete and differ significantly from
modern keyboards; the XT keyboard is not covered in this article.
Next came the IBM AT system and later the IBM PS/2. They introduced the keyboards we use today, and are the topic of this article. AT
keyboards and PS/2 keyboards were very similar devices, but the PS/2
device used a smaller connector and supported a few additional
features. Nonetheless, it remained backward compatible with AT
systems and few of the additional features ever caught on (since
software also wanted to remain backward compatible.) Below is a
summary of IBM's three major keyboards.