Modern fax machines
Modern fax machines have RAM memory just like a computer. As a fax is received, it is temporarily stored in memory, allowing the fax to print the document.
Memory on a fax machine makes it easier to print whole pages. Each page can save into memory, then print out in the same per-page format that it was scanned into the fax with. It also makes it easier to reprint a fax in the event of a paper jam or error while receiving the fax.
Older fax machines
Older fax machines didn’t have any memory or store information – they simply printed the document line by line as the fax signal was received.