The Original 64 bit x86 from Intel Early concept of EM64 T coded name Yamhill the register were extending from 32 bit to 64 bit unlike x86 64 this design do not come with additional general purpose register r8 r15 and lack of 64 bit MMU and address mode support 32 bit address mode with PAE for maximum compatibility with legacy application early Prescott Tejas and Timna were the only implement of this ISA and later is replaced by EM64 T The above text is copied from user 71 57 33 215 without his or her permission but if he or she requests I would remove from my talk page