The third edition is totally focused on 64 bit architecture (GNU/Linux system).
I recently bought this book and I love it. One of the type of books my shelf I know I’ll be going back to.
I read it from a security perspective. I’ve found it beneficial to learn how programs run from the low-level virtual memory system, how kernel/userspace divide works, the endless buffers/caches, etc and how they care all composed together in the OS.
Something that is still useful even as Im mostly working with higher-level code.
I have the 2nd edition (focused on 32 bit) I love it. Next year I would like to buy the third edition, but it is much too expensive, 150$ more or less.