The noun that it stands with -- its gender, number, and case.
Here, we have τα βιβλία which is neuter plural accusative, so όλ- needs an adjective ending for neuter plural accusative as well.
If you had read all the newspapers (which are feminine: η εφημερίδα), for example, then you would have needed the ending for feminine plural accusative, thus όλες τις εφημερίδες.
If it were masculine, what would it be - I guess όλους τυς ?
Nearly: όλους τους.
For example, βλέπουμε όλους τους ανθρώπους "we see all the people".
And what forms are in Genitive, for M, F and N gender?
όλων των (for all three) -- for example, τα βιβλία όλων των κυρίων / τα βιβλία όλων των κυριών / τα βιβλία όλων των παιδιών "the books of all the gentlemen / the books of all the ladies / the books of all the children".
(You can see that των κυρίων "of the gentlemen" and των κυριών "of the ladies" differ in writing only in the position of the accent. The singulars are ο κύριος and η κυρία, respectively.)