Besides, those of the Companions (pbut)

Besides, those of the Companions (pbut) who were literate used to keep a written record of several portions of the Holy Qur'an. In this manner, the text of the Holy Qur'an had been preserved in four different ways during the lifetime of the Holy Prophet (PBUH):
The Holy Prophet (PBUH) had the whole text of the Divine Messages from the beginning to the end committed to writing by the scribes of revelations.
Many of the Companions learned the whole text of the Qur'an, every syllable of it, by heart.
All the illustrious Companions, without an exception, had memorized at least some portions of the Holy Qur'an, for the simple reason that it was obligatory for them to recite it during worship. An estimate of the number of the illustrious Companions may be obtained from the fact that one hundred and forty thousands Companions had participated in the Last Pilgrimage performed by the Holy Prophet (PBUH).
A considerable number of the literate Companions kept a private record of the text of the Qur'an and satisfied themselves as to the purity of their record by reading it out to the Holy Prophet (PBUH).