3600 rpm, with 64 words per track, so reading a word took 260 µs. Minimum cycle time (the address is up next) was 9 × 260 µs = 2.34 ms. Worst case then (just mi

3600 rpm, with 64 words per track, so reading a word took 260 µs. Minimum cycle time (the address is up next) was 9 × 260 µs = 2.34 ms. Worst case then (just missed it) was (9 + 63) × 260 = 18.75 ms.