About Operating Mode? 

Dear Sir or Madam,
I am so sorry to bother you, but I've seen your post on Processor Register, the original text is copied to bellow

| IA32e || 8 || 8 || Early concept of EM64T, 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 EM64T.

That is so interesting and amazing. Besides, I wonder the information on Operating Mode. Is the original IA32e mode a sub-Mode of protected mode or a new mode like it in AMD64? Does the original 32-bit protected OS need to be changed from the scratch or just provides extension support for those new introduced 64-bit instructions? That is most amazing thing for me.

I am sorry to bother you, I was just a computer science student when I knew it and I am merely a computer hobbyist right now. Thank you with my best wishes.