a vague recollection and a bit of googling got me to

http://www.cpushack.net/history.html#1

where the following can be found

"AMD has made many products including CPUs, MCUs, memory. They were a second source to Intel (by agreement) form 1982-1992."

So, by that, one can get that AMD '51s are '92 vintage or older i.e. steam driven.

While not exactly a prime example of up-to-dateness, sometimes a bit of hisory can be found at the above site.

Erik