title: What is the ARM Thumb Instruction set?
body: <p>under "The Thumb instruction set" in section 1-34 of "ARM11TechnicalRefManual" it said that:  </p>
  
  <p>"The Thumb instruction set is a subset of the most commonly used 32-bit ARM instructions.Thumb instructions are 16 bits long,and have a corresponding 32-bit ARM instruction that has the same effect on processor model."  </p>
  
  <p>can any one explain more about this especially second sentence and say how does processor perform it?</p>