I had to look it up, an IBM card format 80x12 is 187x83 mm. Roughly 0.06 bits/mm^2. The CR80 is 86x54mm for the 128bits, 0.03 bits/mm^2. Not a terrible differen

I had to look it up, an IBM card format 80x12 is 187x83 mm. Roughly 0.06 bits/mm^2. The CR80 is 86x54mm for the 128bits, 0.03 bits/mm^2. Not a terrible difference for accommodating hand tools. Edit: If my first search results are to be believed, the first magnetic hard drive had a density of 3.1 bits/mm^2