Does cbexport read through memory or directly from disk?

Hello,

Does cbexport read the documents via memory or directly from disk? In other words, does it first load the documents from disk into memory and then read it from there? If yes, the resident ratio would go for a toss.

Similarly, if anybody can help understand as to how do other utilities like cbbackup, cbbackupmgr, etc. how do those read data?

Thanks