Substituting DSHD for DSDD disks (or DS2D if you prefer)

Fred Cisin cisin at
Tue Jan 26 23:20:48 CST 2016

On Tue, 26 Jan 2016, CuriousMarc wrote:
> You make me feel lucky. I have all 3 (almost, I have the low density HP 
> 9121 rather than an HD 9122 so I can use it on my HP 85)... Haven't 
> restored or even powered up the recently acquired HP 9895 yet, but the 
> HP 82901A and the HP 9121D now work great. Quite low capacity (270k?) 
> due to the weird LIF formatting, formats 35 tracks but uses only 33, out 
> of the 40. I wonder why.

Partially because the original 5.25" drives (Shugart SA400) were 35 track 
(#0 - #34), not 40.

Single sided single density was about 100K.  Double sided double density 
could be up to 400K, with 360K being typical.

> I don't know anything yet about the 8" HP 9895 
> and its encoding. I thought they were surprisingly high capacity (1.2 
> MB?) considering their age. Am I right?

8" double sided double denwsity is, indeed 1.2M or thereabouts, varying by 
format choices.

5.25" "high" density mimics 8".

One company, NEC, made their 5.25" "high density" format the same as 
their 8" format, and even ran their 3.5" drives at 360RPM, instead of the 
more common 300RPM, so that they could have the same format on those, 

Grumpy Ol' Fred     		cisin at

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