Ordering details for the Intel architecture documentation are at https://software.intel.com/en-us/articles/intel-sdm - the volumes range from $8 to $23 depending on size. I think the documentation was free when I got it but times have changed. Edit: you can download the PDF (for free) from that link too.

It's quite a surprise to go to HN and see my post from 2013 here, by the way.