On 09/30/2017 06:29 PM, Jon Elson wrote: > Ahh, but the genius is built into the heads! Note that nobody > recorded 800 BPI on 7-track tapes. I think they supported 200 and 556 > BPI, only. There were some low-density 9-track tapes, but generally > most 9-tk tapes were 800 BPI. Say what? We certainly did a lot of tape at CDC at 800 NRZI on the 607s.657 and 667. Most IBM 729s, but for the very early models could support 800 NRZI.
800 NRZI for 9 track was common only until about 1970; 1600 PE was available on the 2400 series. By 1975, it had pretty much become the 9 track interchange standard. In spite of packing more data on a piece of tape, 1600 PE is actually more reliable than 800, as a dropped bit transition doesn't corrupt data downstream. --Chuck
