The Art of Computer Programming in PDF form can be found on The Pirate Bay, and I encourage anyone who can't afford it (students, programmers between jobs, etc) to download it. But if you feel you learn anything from it, then you must buy it later once you have the income.
Also, it's probably ethical that if you've bought TAoCP, then it's ok to download it in PDF form. Some people like PDFs instead of hardcopy.
I find PDF formatted books so difficult to use, I will reach for the paper version first :( But as discussed above, SICP does seem to be available in a convenient digital format.
Also, it's probably ethical that if you've bought TAoCP, then it's ok to download it in PDF form. Some people like PDFs instead of hardcopy.