title: Can the lower byte of the registers RSI, RDI, RSP and RBP be directly addressed in the 64-bit Intel processors?
body: <p>In the 16-bit Intel processors (8086, etc...) the registers SP, BP, SI, DI were 16-bit registers and could only be addressed as 16-bit registers.</p>
  
  <p>32-bit processors have extended this registers to 32-bits (referred as ESI, EDI, ESP, EBP) and these registers could be used as 16-bit registers for backward compatibility.</p>
  
  <p>Few resources state that these registers are now byte addressable (as SIL, DIL, SPL, BPL) in the <strong>64-bit Intel processors</strong> and few resources doesn't. I'm confused!</p>
  
  <p>Is this an added feature along with the addition of R8-R15 registers ?</p>
  
  <p>*byte addressed = lower byte of the register.</p>