Official Intel manuals
For long time, Intel offers download of its x86 architecture manuals for free. The most important are Instruction Set Reference manuals and Basic Architecture manual.
Official AMD manuals
AMD offers download of its x86 architecture manuals for free as well as Intel. Application Programming manual serves as Intel's Basic Architecture manual. General-Purpose and System Instructions serves as Intel's Instruction Set Reference manuals.
The world's leading source for pure technical x86 processor information.