the B-29 planes had been within the intense nuclear radiation zone when the bombs exploded over Hiroshima and Nagasaki, then they would have suffered effects from the charge separation (radial) EMP
^the emp only spreads as far as the nuclear radiation... there is a less powerful emp that spreads a bit (in comparason to the explostion) further then the radiation but not enough to destroy electic devices.
the B-29 planes had been within the intense nuclear radiation zone when the bombs exploded over Hiroshima and Nagasaki, then they would have suffered effects from the charge separation (radial) EMP
It won't wipe the hard drive, but it will probably damage the laptop generally.
And an EMP would kill a computer, even if it is off. In the same way you can fry your motherboard by not grounding yourself (which I admit is difficult to do nowadays, but EMPs are hundreds times stronger than the static you can easily build up yourself).
I have tried a few of these tests, only time I could corrupt my drive is when i passed a magnet, rather strong magnet, could attract metal through 3 inchs of wood... across the drive, but going straight to and from it for some reason didn't harm it at all.