Why are magnetic hard drive bits written as wave structures?

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Llama77
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I understand the general aspects of how a hard disk drives works. I have gone deeper and have learned about the various types of magnetoresistance, both AMR and GMR. I understand the fundamentals of how these systems work compared to older units.

But people keep telling me that the data that is actually written to the platters ferromagnetic material is in the form of a wave like structure.


id like to better understand this, thank you.
 

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Any varying signal is basically a wave, to record it in binary = ones and zero = a wave with sharp edges, this takes more bandwidth.
To get the most data in the least space you want to minimize wasted bandwidth - this means the smoothest signal that is distinguishable from a pure tone.
 
Im still a bit confused. So any signal is wave like, so all magnetic fields are wave like? If they are wave like, how does the system tell them apart.
 
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The data is a time varying signal at the read head and a position varying magnetic field on the disc.
You could record them as a series of ones and zeros but as we desccribed that is an inneficient use of the bandwidth.
The encoding schemes are very complex in practice - the simplest is probably MFM (http://en.wikipedia.org/wiki/Modified_Frequency_Modulation)