29.15.1.1. Intel 64 and IA-32 Architectures Software Developer’s Manuals
We are using the May 2019 version unless otherwise noted.
There are a few download forms at: https://software.intel.com/en-us/articles/intel-sdm
The single PDF one is useless however because it does not have a unified ToC nor inter Volume links, so I just download the 4-part one.
The Volumes are well split, so it is usually easy to guess where you should look into.
Also I can’t find older versions on the website easily, so I just web archive everything.