title: Register length, Memory Size and 32/64 bit computing (MIPS)
body: <p>I am currently studying the MIPS processor. Since I don't have any previous knowledge in computer architecture, I am a little bit confusion about the some basic concepts of the MIPS ISA. </p>
  
  <ol>
  <li><p>When we talk about 32-bit vs 64-bit computing, what is the actual definition?  Some people say it determines the word length while others say it determines the register length. As far as I know, MIPS32 has a 32-bit register while MIPS64 has a 64-bit register. However, they both handle 32-bit words and instructions, so is MIPS64 32-bit computing or 64-bit computing?</p></li>
  <li><p>MIPS32 can address up to 2^32 addresses in the memory. It is because the memory address length is 32 bits. How about MIPS64? What is the address length for the MIPS64 memory architecture? Is it 32 bits or 64 bits? I don't know whether there is a relationship between register length and the addressable memory space. If there is, I will be so thankful for any explanation.</p></li>
  </ol>
  
  <p>Thanks!</p>