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A machine instruction is a pattern of bits that asks for one machine operation to be executed.

Setting up SPIM

Spim Options

Each MIPS machine instruction is 32 bits (four bytes) long. The three lines after main: call for three machine instructions. The remaining lines consist of information for the assembler and comments (for the human).

For this first program some SPIM options must be set. For Windows, in the menu bar, click on Simulator then Settings to get the settings dialog. For Mac, in the menu bar, click on QtSpim then Preferences to get the settings dialog. Select the following options:

ON Save window positions
ON General registers in hexadecimal
OFF Floating point registers in hexadecimal
ON Bare machine
OFF Allow pseudo instructions
OFF Load trap file
ON Delayed Branches
ON Delayed Load
ON Mapped I/O
OFF Quiet

These settings simulate a bare machine with no user conveniences. Later we will include the conveniences.


(Thought Question) Do most actual computers start up as a bare machine?