Each age has had its own understanding and preferred metaphor for how the human mind stores, manages, and uses information. Each age that has actually thought about it.
Our electronic age conceives of the mind as a computer plugged into a host of peripherals, wired and connected.
The medievals imagined the mind to be an ark in which information, like goods, are carefully stowed in different parts of the vessel. Like books on the shelves of a medieval library, the human mind, on this understanding, arranges memorable material, the memoranda of the mind, using a carefully conceived filing system. Many medieval scholars tried to explain how this works. All of these theoricians were consummate practicians of the art of remembering. In an age of scarce written information, reading was a resource to be exploited on the spot. Make the most of a book while you have it and you read it, as you might not see it again.
Thus, reading was elevated to the status of a high cognitive art. While we don’t give much thought to reading – it’s such a casual activity – our ancestors took it seriously. They identified good and bad ways of reading, based on the mnemonic outcomes of each. A bad way of reading would prevent the reader from extracting and retaining most of the meat of the book. And in a culture without refrigeration or hard drives, retention and conservation, for the purpose of later consumption, was key.