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The RAT and the Register File

Modern CPUs track far more register values than they have register names.

This is the eighteenth video in Part 3 of the Performance-Aware Programming series. Please see the Table of Contents to quickly navigate through the rest of the course as it is updated weekly. The listings referenced in the video (listings 141, 142, and 143) are available on the github.

As mentioned in the video, I have never been able to get a definitive answer on what RAT stands for. In Intel architecture diagrams, it is often “Register Alias Table”. Other times, in papers and textbooks, it is referred to as a “Register Allocation Table”. I believe I have also seen “Register Assignment Table”. There may even be more “A” options I simply haven’t encountered yet. “Register Allotment Table”, anyone?

So, please feel free to make up your own acronym expansion. We know it’s the RAT, and (after this video) we know what it does… but we may never know what it stands for!

Also, as mentioned in the notes, hand-drafted transcripts are no longer produced for course videos. An automatically-generated transcript of the video — likely containing some errors — is included here for reference:

The full video is for paid subscribers

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