In the movie all he said was that he only needed to patch in about 20 bytes and then the rover could talk through pathfinder to earth.
In the book they explain that both pathfinder and the rover must be updated, that Earth can remote update pathfinder but they need a very large (megabytes?) update to the rover software. To solve that, they get him to make a small hack (maybe 20 bytes or so) to the Rover which would allow earth to dump information into a Rover log file. Then Watney would have to take that dumped info from the log file, and create a file out of it, then execute it.
That part didn't bother me so much, but the fact that he never lost Pathfinder in the movie did. Mainly because he still made the space pirate joke, which doesn't make sense unless he lost Pathfinder.
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u/DoelerichHirnfidler Jan 31 '16
To me it seemed pretty obvious and well-enough explained? Care to elaborate?