With some quick math, about 2283 microSD cards will fit within the volume of a 3.5" hard disk. Assuming 10% of that space is lost for casing, connectors, etc., 2000 should be possible, which gives 1PB.
If price was not an issue, we would be able to have 1PB in the form factor of a 3.5" hard disk.
It was only 14 years ago that SanDisk launched the 1GB SD card, with a suggested retail price of $499.99.
So maybe in 2032, we’ll see the worlds first 1PB memory card . . .