A little HP9877 info - test-drb@ccmp.vtda.org

29 Jun 2001

ard(a)p850ug1.demon.co.uk (Tony Duell) wrote:
...
  If the 9815 encoding is idential physically the 9825
one (that is to say, 
 a 9815 tape read at the 9825 speed contains the data encoded as above 
 with the same frequencies as the 9825 uses) then the 9877 can read it. If 
 not, then IMHO it can't. And since the 9815 and 9825 tape controllers are 
 very diferent, I think it's unlikely that the 9877 (which uses a 
 controller that's essentially the same as the 9825 one) can handle 9815 
 tapes. Pity. 
Here's a snippet from _Mid-Range Calculator Delivers More Power
at Lower Cost_, by Douglas M. Clifford, F. Timothy Hickenlooper, 
and A. Craig Mortensen, in the June 1976 HP Journal:

"...It was determined that a level of performance below that of the
9825A Calculator (see article, page 2) would be adequate, so the
search speed was reduced to 60 ips and the read/write speed to 10 ips.
The recording density was set at 500 bits per inch.  Because of these
reduced demands all of the encoding and decoding of the bits can be
done in firmware.  Also, a frequency-lock control loop is used for the
motor control instead of a more costly dc servo (more about this
later)."

Does that give you any clues?  Unfortunately I don't think it says
anything about the recording density of the 9825 tapes.

-Frank McConnell