I will give you one case in point, the guy who told me about this one, was emphatic that I use real names on my site. I am not vindictive, and anyway the internet is no place for hurting people, but if you're the one spreading this manure, please find a face saving way to stop. My friend was in a computer store that sold individual componets, hard drives in this case, and he was told that the drive in question would not work because Apple drives change the rate of the spindle speed rotation to compensate the head distance travled such that for any given head position cylinder and the circumference it must travel, the effective head to surface speed remains constant. OK I'm game, didn't Mac floppy drives do that years ago? But a hard drive? See a floppy drive rotates the disk in the vicinity of 300 rpm, and average seek time is in the range of 70 milliseconds, so you move the head and go from say 250 rpm, to 350 rpm, allow for spindle speed stabilization, maybe a tenth of a second, and you've only added 30 milliseconds or thirty percent roughly. Small hard drives for laptops spin 4000 to 10000 rpm battery life is an issue here, spinning up a hard drive quickly wastes more power than gently ramping up to speed. Ditto for arbitrarily shifting speed. So they take a second or two to spin up, depending on the drive, you can hear them spin up if you listen carefully as you power up a laptop. Also the window of time is orders of magnitude shorter for head movement in a hard drive, something the drive makers are proud to advertise, sub-millisecond head motion is a big plus. If they changed the spindle speed everytime they moved the head, and waited for it to stablize, even if they could do it in less than a second, they would be offering slower track to track seek times than their competition by a factor of a thousand! Just knowing the smallest detail can often put silly notions to rest. ========================================================================== It is noteworthy that the 3 1/2 inch microfloppy disk is the only magnetic disk format where variable speed recording has been widely used. Because floppy disks have very low angular momentum, they can spin up to the desired speed in about the time it takes to seek halfway across the disk. The Apple SuperDrive for the 3 1/2 inch floppy allowed the disk to spin at variable rates, and this allowed Apple's High Density format on this size floppy to store 800K where the rest of the industry only managed 720K. ==========================================================================