One of the system gurus at the ECN amused himself one late evening by writing a small program on the PDP 11/70 that would seek from the beginning of the disk pack to the end, with a short wait between seeks. He had it read the amount of time to wait from the front panel switches, and then diddled with the switches until he found the resonant frequency of the drive *housing*. The drive, which was free-standing, must have weighed several hundred pounds, and stood about waist-high. It held 88Mb, if I remember correctly. He got so good at controlling the thing that he could sort of walk the drive across the machine room floor. I can only imagine the look on the DEC field service engineer's face the first time he saw