Because the book is essentially a series of collected magazine articles the section on Quake development will have one chapter that reads "hey, this is what we're going to do!" followed by "well, that didn't work, but this does!". One important aspect of post-mortems and development journals that I find is frequently missing is a detailed look at what didn't work technically and why, which it has in spades.
edit: The book is also available as a free download: http://www.drdobbs.com/high-performance-computing/184404919
Too bad it's out of print, and they didn't do any subsequent editions.
Abrash did amazing things with assembly to get Quake to run on the 486.
I don't know if Carmack, Abrash, or someone at SGI (it's in OpenGL source code too) came up with it; but it seems like witch craft to me.
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