It is a 5 MB Hard Disk Drive for the IBM 305 RAMAC, the first IBM 'SUPER' computer released in September 1956.
This HDD weighed over a ton and stored an 'astonishing' (@ the time) 5 MB of data.
Do you appreciate being able to reach into your pocket & pull out your 8 GB memory stick now - or perhaps even your 3GS iPhone with 32 GB of memory?!?
Something to think about, huh?
(click on the title of this post to go to "Snopes" for more information on this photo)