They do a lot of takes...He writes a piece...They record...He writes another piece...They record again...
Once you have done it a few times, you know the entire song in your head...
When Jay Z says he doesn't write his lyrics, it impresses Jigganauts, but they forget that he is probably doing several takes...He may not use a pen and paper, but he is using a recorder to memorize the bars for him...
On the other hand, Pac would write his shyt, record it, and move on to the next song...
This is how the GOAT contenders RUINED hip hop...They turned hip hop from a custom made artform in specialized boutiques...To mass produced waterdown artform straight from "Wal-mart"...