AFAIK, the 10 internal registers were first mentioned by Robert Collins in this article: https://www.rcollins.org/articles/loadall/tspec_a3_doc.html https://www

AFAIK, the 10 internal registers were first mentioned by Robert Collins in this article: https://www.rcollins.org/articles/loadall/tspec_a3_doc.html https://www.rcollins.org/articles/loadall/tspec_a3_doc.html They're only mentioned for the 80386 version of the LOADALL instruction though, where he confirmed that the CPU actually does bus cycles to read them. But the same registers already existed on the 80286 (only 16 bits of course). On that chip they are the 3 words before and 7 words after the MSW, the ones marked as "None" in the table there (note that it is slightly wrong, MSW should be 806H instead of 804H).