When and how was the Qur’an divided into sections?

The term "Hizb al-Qur'an" (partitioning of the Qur'an) has two meanings: The first is the daily portion or amount that a person recites to complete the Qur'an, which the Salaf (early Muslims) divided over the days of the week. The second is half of the well-known juz' (part), as the Qur'an was divided into thirty juz's, and each juz' contains two hizbs. This division was an ijtihadi (based on independent reasoning) effort to facilitate memorization and revision.