Explanation of the Program

There are various ways for a program executing on a real machine to return control to the operating system. But we have no OS, so for now we will single step instructions. Hopefully you are wondering how the program works. Here it is again:

## Program to add two plus three 
        .text
        .globl  main

main:
        ori     $8,$0,0x2       # put two's comp. two into register 8
        ori     $9,$0,0x3       # put two's comp. three into register 9
        addu    $10,$8,$9       # add register 8 and 9, put result in 10

## End of file

The first line of the program is a comment. It is ignored by the assembler and results in no machine instructions.

.text is a directive. A directive is a statement that tells the assembler something about what the programmer wants, but does not itself result in any machine instructions. This directive tells the assembler that the following lines are ".text" -- source code for the program.

.globl main is another directive. It says that the identifier main will be used outside of this source file (that is, used "globally") as the label of a particular location in main memory.