The best images for showing the scale of the smallest drive are from the comments (on the AppleFritter site).
Just for laughs someone should make a 39 inch drive with modern technology. Looks like a PMR drive would get 338 TB per platter, so a 25 platter arrangement like in the photo would be 9.7 PB.
From the article:
> The platter is 39" diameter and 1/4" thick. It is made of magnesium.
My brain initially read that as "made of momentum"...