HP 7970E - interest to split?

Jon Elson elson at pico-systems.com
Sat Sep 30 23:22:07 CDT 2017


On 09/30/2017 10:31 PM, Chuck Guzis via cctalk wrote:
> 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.
>
>
OK, I never used 7 track tapes, but I thought that they were 
recorded at lower density than 9 track.
Yes, I know about 1600 PE, 3200 PE and 6250 GCR.

Jon


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