For anyone looking to pick up Computer Systems: A Programmer's Perspective, you should probably avoid the Global Edition. From the author's website [0]:
> Note on the Global Edition: Unfortunately, the publisher arranged for the generation of a different set of practice and homework problems in the global edition. The person doing this didn't do a very good job, and so these problems and their solutions have many errors. We have not created an errata for this edition.
If you can't afford the book, it seems like the First North American Edition is available on the Internet Archive, although I'm uncertain of its legality. Remember to support the authors, if not now then hopefully in the future after you get a high paying software engineering job.
I haven't read each edition in order to make a comparison. However, it's probably worth mentioning that, unlike the 3rd edition, the solution manuals for both the 1st and 2nd editions can easily be found online with a quick search. If you intend to sit down and start solving problems then the 2nd edition might be better, since you'd be able to check your answers against the solution manual.
Edit: I actually hadn't looked, but it looks like all the solutions for the 3rd edition are also available online [0].
This book looks interesting, but it's unfortunate that there's no way to get the instructor's book for the answers to the exercises. Sort of diminishes the value of the book for self-learners.
The solution manuals for the 1st and 2nd edition are both easily found online with a quick search. As for the 3rd edition, I was able to find this [0], although I haven't verified if their answers are correct.
But it would appear that you're correct that Pearson doesn't seem interested in selling the 3rd edition solution manual to anyone that isn't an instructor [1]. IMO, fuck their antiquated gate-keeping bullshit.
> Note on the Global Edition: Unfortunately, the publisher arranged for the generation of a different set of practice and homework problems in the global edition. The person doing this didn't do a very good job, and so these problems and their solutions have many errors. We have not created an errata for this edition.
If you can't afford the book, it seems like the First North American Edition is available on the Internet Archive, although I'm uncertain of its legality. Remember to support the authors, if not now then hopefully in the future after you get a high paying software engineering job.
[0] http://csapp.cs.cmu.edu/3e/errata.html