9895A vs 7902A ?

Al Kossow aek at bitsavers.org
Fri Sep 23 01:08:12 CDT 2005

just found an answer to the differences.

there is a partial 7902/9895 manual hp_floppydisk_7209xx.pdf
on dyndns.org that has the history


This service manual contains service information for the 7902A, 9895K 
and the 7902C
flexible disc drives and the controller boards used on the HP 250, 300, 
1000, and 3000
series 30 and 33 systems. The following brief history describes the 
changes that have taken
place on the disc drives and controller boards and the reasons for the 

The first production model 7902A flexible disc drives were installed in 
the HP 250, 300 and
3000 systems. The 7902A drives (P/N 07902-68811) designed for use in 
the HP 250 and
the 7902A drives (P/N 07902-60038/07902-60023) for use in the 300/3000 
were non-
interchangeable. For this reason a common drive (P/N 07902-67914) was 
developed as a
replacement. Refer to service notes HP 250-01 and 7902A-01 for 
instructions if one of the
old drives is discovered in the field. In the past, the drive 
mechanisms for the 7902A had
been manufactured by Shugart and utilized a tri-compliant head design. 
As of September,
1980, this drive was replaced with one using a bi-compliant head design 
used on the

The drive used on the 9895K is built by CDC and utilizes a 
tri-compliant head design. These
drives are not interchangeable between systems because of differences 
in drive boards used
on the various systems. The drive boards used on the HP 300/3000 
systems are designed
and built by HP and utilize control signals which are non-industry 
standard. The drive
boards used on the HP 250 systems are designed and built by both 
Shugart and CDC and
utilize industry standard control signals.

The controller board (P/N 45000-66510) used on the old HP 250 systems, 
and the control-
ler board (P/N 07902-60024) used on the old HP 300/1000/3000 systems, 
were also non-
interchangeable and they both utilized in MC2 micro CPU. A new 
controller board (P/N
07902-6652(1) was designed as a replacement for the 45000-66510 board. 
If one should
fail in the field, refer to service note 07902A-5A for instructions. 
The controller board used
on the old HP 300/1000/3000 systems (P/N 07902-60024) is 
interchangeable with the new
controller board (P/N 07902-66501) designed for use with the 7902C. The 
new HP 3000
systems no longer use the 7902 disc drives. The 9895A flexible disc 
drives will be used in
place of the 7902.

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