How heavy is your data?

PC Pro received a funny question: just how heavy is the data on your disk drive?

Can you tell me whether a full computer hardrive weighs more than an empty one ? And if it does what does the extra weight comprise of?

Again, I know it’s a strange question, but I would be v grateful if you could shed some light!

The same question is up at superuser.com, and has actually received some semi-serious responses. In fact, the question is pretty common; and the answer is: there is no significant change in the mass of your hard drive. According to some people, there are minute effects due to the changes in the magnetic field, but whether or not that is true and actually measurable is up for discussion.