Note that this is different from some other assembly languages that you might be familiar with. Notice that the format is quite rigid-you can only add two items, and store the result in a single destination. This might be different from some of the high level languages that you are used to, and may require you to add a larger number of operands using multiple steps. Work through the examples on pages 96 and 97 in your groups. A constraint imposed by the MIPS architecture is that the operands of arithmetic instructions can only be registers .
Registers are a small set of on-chip locations that can be accessed very quickly by the processor.
Each of these registers is 32 bits or a word in length. A bit string of length 8 is called a byte . A bit string of length 16 is called a short-word . A bit string of length 32 is called a word . Note that some authors refer to the 16 bit length as a word, and the 32 bit length as a long-word, but we'll stick to the book's terminology.