View Single Post
Old 22 December 2013, 14:26   #25
IFW
Moderator
IFW's Avatar
 
Join Date: Jan 2003
Location: ...
Age: 45
Posts: 1,838
Mark_k,
Pre-compensation is for writing data.
What you write to a disk is often not what you want to read... certain bitcell combinations - if they are close enough - cause peak shifts, meaning making the flux transitions that make up the bitcell to appear closer or farther away than how they should be.
Pre-compensation means that affected bitcell patterns have some of their flux transitions advanced or delayed, effectively making the data during read behave as expected, rather than causing peak shifts.
Hardware based pre-compensation (e.g. Amiga or most generic FM and MFM controllers) is fairly simple and is limited to pattern matching and preset values.
Software based pre-compensation such as what Trace or KryoFlux uses are significantly more sophisticated as the data window is not limited to just 5 bitcells like in most hardware. (previous-1, previous, actual, next, next+1 bitcell)

There is also post-compensation, which is getting rid of peak shifts by assuming how the flux timings behaved based on their distance.
That is data recovery realm, and not something an Amiga could even attempt to do...

Last edited by IFW; 22 December 2013 at 14:32.
IFW is offline  
 
Page generated in 0.04914 seconds with 9 queries