if you wanna get into byte copying, from a legal view, isn't also copying from disk to memory a copy of the book then ?
The law says that copy is something that is "fixed" on a tangible medium. DRAM might not fall under that definition.
It does if the copy is "more than transitory". Software in RAM is a full copy and remains there as long as the program runs, so that can be an unlicensed copy per MAI v Peak (but if you had a license to the original, there's an explicit legal carveout for RAM copies). It would depend on how far the data is buffered and how long it is cached.