On 06/05/2018 01:29 AM, Christian Corti via cctalk wrote: > Just a guess, but 556 kHz is 5 MHz divided by 9. Actually, it's a repeating decimal 555.5555.... And we're talking bits/chars per inch, so I don't see the connection, particularly on a 75 ips drive. More guesses welcome! This one's been dogging my mind for nearly 50 years, so I'm the patient sort... --Chuck