So I just finished watching the first video. While there was a lot of stuff I already knew about from previous interviews, I really appreciated the breakdown of how Crash got around the memory limits.
The PS1 disc could hold 640mb data but only 1 MB could ever be accessed instantly. They didn't stream directly from the disc since it would take 6 seconds to access 1 MB every time, so what Gavin did was give PS1 instructions to break up the memory into smaller chunks (or pages) and each chunks would stream whatever data they actually needed at a certain time.
A lot of games on the original PS1 never made use of the disc except for music or video, because they just fit all their assets in the 1 MB memory and call it a day. But Naughty Dog did want to use all 640mb space and stream it to the memory, giving the impression of a much larger game than what was possible.
Very innovative and forward thinking use of limited technology back then. Gavin also explained in the video that it was not always the Playstation's fault why some games had very limited graphics. He explained that the original code or library the PS1 shipped with only used like 33% of the GPU. Naughty Dog basically had to go in and rewrite the code themselves to get access to the complete 100% of the actual power available.