This is an update to fix a few typos found in the first three chapters. Other than that, there are cosmetic changes to the diagrams and page layout. Text leading has been reduced and page margins adjusted. Denser flow of text has brought the page count down from 939 to 795. Have fun reading, watching the videos, and playing with the REPL!
Here is the updated PDF. (Previous version still available.)
EDIT 2012/11/25: newer version of the PDF.
The PDF version of the classic MIT 6.001 computer science textbook Structure and Interpretation of Computer Programs (SICP), 2nd ed. by Abelson, Sussman & Sussman just got better.
The typography has been modernized for better on-screen legibility and comfort. All the mathematics is set in proper TEX, and figures redrawn in vector graphics.
It is an improvement of the Unofficial Texinfo Format (UTF) which was converted from the original MIT Press full text release by Lytha Ayth and maintained by Neil Van Dyke.
You can learn more about the new ebook, use the source, or read the PDF.