50Hz vs 60Hz fixed drive speed ?

Tom> Well if you are talking about modern hard drives, then you are Tom> of course correct. But then that wouldn't be on topic for this Tom> list. My question revolves around the old vintage hard drives Tom> with fixed platters driven by A/C motors. One data point: at least some of the DEC head-per-track fixed disks -- RS64/RC11 and RF11 -- were constructed with spindles just like modern hard drives, the motor and platter bearing assembly all a single unit. In other words, there aren't any pulleys or the like in that setup. But the motors were AC motors, so in that case you'd definitely end up with a rotation speed dependent on the power line frequency. I don't know if the 16% difference was big enough to require tweaks to the drive electronics -- the PLL in the data recovery circuit, specifically. Perhaps so. paul