Re-order buffer

A re-order buffer (ROB) is used in a Tomasulo algorithm for out-of-order instruction execution. It allows instructions to be committed in-order. A re-order buffer (ROB) is used in a Tomasulo algorithm for out-of-order instruction execution. It allows instructions to be committed in-order. Normally, there are three stages of instructions: 'Issue', 'Execute', 'Write Result'. In Tomasulo algorithm, there is an additional stage 'Commit'. In this stage, the results of instructions will be stored in a register or memory. In the 'Write Result' stage, the results are just put in the re-order buffer. All contents in this buffer can then be used when executing other instructions depending on these.