This drawing represents 512 CDC SMD 300 MB drives. I've installed more than that at libraries all over the USA.
How much can this store?
Multiply 512 drives time 300 MegaBytes (300,000,000) and you get 153,600,000,000 Bytes, ( 154 Gigabytes)
A modern little USB drive is 4 Terabytes.
It holds as much as 25 rooms full of those old 1980 era drives.