World's Thickest Book

Intel should publish all of their documentation, including

http://www.intel.com/content/www/us/en/architecture-and-technology/64-ia-32-architectures-software-developer-manual-325462.html
and
http://www.intel.com/content/www/us/en/architecture-and-technology/64-ia-32-architectures-optimization-manual.html

in one book.

>>21
Backwards compatibility is very important, and is one of the main reasons to choose x86. The older addressing modes are well known and no more "time and money" needs to be spent on them anyway, since they essentially copy+paste much of the design from the previous generation for their base.

They're probably still mad at AMD for making a horrible mess of what they wanted the 64-bit mode to look like. There are so many empty spaces in the opcode map that could've been used for 64-bit extension prefices, and segment descriptors have additional empty bits that could've easily accommodated 16, 32, and 64-bit coexistence, letting you use 64-bit operations in real mode just like it was possible with 32-bit, but they decided to overwrite an entire row of register inc/decs and introduce entirely incompatible operation modes.

But pissing off Intel by trying to make them start over with the architecture was probably a bad idea. And they had to put back some of the stuff they stupidly "left out" but was always there, since the circuitry is still present on die!