Note: the author means that caching can be used as an implementation detail in an (abstracted) storage access system, as opposed to a baseline of having multiple storage systems (fast, medium, slow) and managing them directly.

This was confusing to me – the most obvious way to judge the purpose of a system is to compare with the baseline of not having that system at all, especially in the case of caching where the program is functionally complete and correct without a cache. Anyway, there may not be a right or wrong here. Just tripped me up.