On Mon, 24 Nov 2014, Chuck Guzis wrote: Verification with the same modulation as it would eventually be used with would seem to provide marginally better trustworthiness. Similarly, single sided and double sided disks were the same cookie, just not necessarily "guaranteed" for the second side. BUT, there were RUMORS that SOME manufacturers had high failure rates; so high that they tested both sides of the cookie. If both sides passed, then they sold them as "double sided". If only one side passed, they flipped to the correct side, and sold it as "Single sided". If neither side passed, then they sold the cookie to Wabash. I'm sure that Wabash denied using other manufacturers dumpster content.

I have had 5.25" disks that would apparently format reliably at 48tpi (40 cylinders) but not at 96tpi. I guess it was that the magnetisation level was marginal anyway and you didn't get enough signal back with the narrower head. No, I didn't trust them, not even at 40 cylinders I remember similar issues with audio recording tape, some would be OK (just) for 2 track recording and useless for 4 track. -tony