Enigma: Scheme B, behaviour on a real 1541: failure rate of variant 2 withdrawn (read model corrected, results contradict; not verified on hardware)

2026-11-09T08:36:46Z

Scheme B, behaviour on a real 1541: failure rate of variant 2 withdrawn (read model corrected, results contradict; not verified on hardware)

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	Variants 0 and 1 are deterministic. Variant 2 is not: error 27 is not written onto the disk. The headers on track 35 are fine, and the error comes from the drive reading them at the wrong bit rate.		Variants 0 and 1 are deterministic. Variant 2 is not: error 27 is not written onto the disk. The headers on track 35 are fine, and the error comes from the drive reading them at the wrong bit rate.

	~~This~~ was ~~evaluated~~ with a model of the 1541 read electronics and DOS, applied to the KryoFlux streams of all scheme B releases. The model includes the job code, sync timeouts and the full retry chain with head offsets~~. It~~ returns exactly 21, 22 and 00 for tracks 33, 34 and the normal track 18. For track 35 at nominal drive speed, the DOS reports 27 in ~~about~~ 83-98% of the reads~~, depending on~~ the ~~disk; otherwise it reports mostly 20, sometimes 23~~. If the ~~disk turns~~ 1-2% slower ~~relative to the drive clock~~, ~~this drops to 42-~~93%. So on a real ~~C64 about 1-6% of all program starts fail~~ the ~~check, and more~~ on ~~slow drives~~. ~~This has not been measured~~ on real ~~hardware yet~~.		How often variant 2 fails on a real drive could not be determined. It was simulated with a model of the 1541 read electronics and DOS, applied to the KryoFlux streams of all scheme B releases. The model includes the job code, sync timeouts and the full retry chain with head offsets, and returns exactly 21, 22 and 00 for tracks 33, 34 and the normal track 18. For track 35 the results contradict each other:
			* With the exact digital circuit of the 1541 (as emulated by VICE for P64 images, without analog noise), the dumps of [[Hohner Midi Sequencer]] and [[Korg Poly 800 II Editor]] give error 27 in 72-99% of the reads at nominal drive speed. The dumps of [[Track Star]], [[Pro16]] 2.4 and [[Pro16 PLUS]] V2.4 read track 35 too well: the DOS reports 23 (data block checksum) or no error at all, so variant 2 would never pass, as in VICE with the P64.
			* An earlier model with more timing noise gave error 27 in 83-98% of the reads for all disks.
			* A drive speed difference of only 1% changes the result a lot (e.g. [[Korg Poly 800 II Editor]] side 0: error 27 in 0% of the reads at 1% slower disk rotation, 93% at nominal speed, 100% at 1% faster rotation).

			Since the original disks were sold and used, a check that never passes on some of them is unlikely; the analog noise of a real drive is probably what makes the misread produce error 27. A test on real hardware is needed. Until then, the failure rate of variant 2 on a real drive is unknown.

	Note: the KryoFlux streams of these disks were captured at 360 rpm. Normalise the timing to 300 rpm (200 ms per revolution) before analysing them.		Note: the KryoFlux streams of these disks were captured at 360 rpm. Normalise the timing to 300 rpm (200 ms per revolution) before analysing them.

Enigma: Steinberg Research protections: scheme A (hidden track 37, key sector, KERNAL requirement) and scheme B (read errors on tracks 33-35, real 1541 behaviour, VICE, patched G64s)

2026-11-08T23:28:14Z

Steinberg Research protections: scheme A (hidden track 37, key sector, KERNAL requirement) and scheme B (read errors on tracks 33-35, real 1541 behaviour, VICE, patched G64s)

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2026-11-08T23:14:10Z

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Steinberg Protection - Revision history

Enigma: Scheme B, behaviour on a real 1541: failure rate of variant 2 withdrawn (read model corrected, results contradict; not verified on hardware)

Enigma: Steinberg Research protections: scheme A (hidden track 37, key sector, KERNAL requirement) and scheme B (read errors on tracks 33-35, real 1541 behaviour, VICE, patched G64s)

Enigma: Created page with "text"