P64

[BeRo]

I'm the designer of the P64 file format, and one of the authors of the new 1541 drive emulation logic code in VICE (and Micro64).

And why P64 files are not big:

1. The P64 files contains the raw NRZI flux pulses, but only the actual existing NRZI flux pulses in a sparse array list (and as linked list while emulation run time, for fast insertions and deletions of NRZI flux pulses at emulated write accesses), and not in a dense array list.
   
2. And the P64 files are encoded with a range coder, so they are basically compressed. The range coder stuff is also descripted in the P64 file specification.
   

And the 1541 drive electronics has a lowpass-filter-like valid pulse detector, which only passes pulses that are at least 2.5 microseconds in duration. Any pulses than 2.5 microseconds are suppressed, so this effectively rejects any noise above 400 kHz. So 16 MHz sampling rate at circa 300 RPM +/- are really more than enough here.