I'm counting only the highest available capacity drives in 3.5" format. If you mix various physical sizes it changes the overall tendency quite a bit. Until aro

I'm counting only the highest available capacity drives in 3.5" format. If you mix various physical sizes it changes the overall tendency quite a bit. Until around 1999 (availability of 50GB 3.5" drives) the biggest available drives were 5.25" (up to 43 GB). 5.25" drives were also much more common than 3.5" drives during all of the 80s. That's why I'm counting starting in 1990, which flattens the curves.