Explaining data storage in a visual way has always been difficult, but especially so with the transition to magnetic tape in the 1950s and 1960s.
Photographs of punched cards help show the enormity of the task at hand, and also the materiality of the information.
5 megabytes of data seems pretty insignificant nowadays, when terabyte hard drives are a common feature in personal computers.
1 TB = 1,000,000 MB (now that would be a lot of punched cards!)
From the Computer History Museum’s online exhibit on Memory and Storage