HP drives

Tony Duell ard at p850ug1.demon.co.uk
Tue Dec 28 12:45:18 CST 2010

> > On Sun, 26 Dec 2010, Chuck Guzis wrote:
> > > I find it more interesting that some of the 135 tpi users selected
> > > odd values for the upper limit.  HP used 66, I think and Jonos used
> On Mon, 27 Dec 2010, Christian Corti wrote:
> > HP used 35 for their 5.25" DS drives (e.g. HP82901) and 70 for their 3.5"
> > SS drives (e.g. HP9121).
> 35 was, of course the original Shugart SA400.  I guess that HP never heard
> about, nor believed in, the extension to 40 of the "standard".

Years ago somebody tried to tell me that '35 track' 35.25" disks had a 
smaller head slot than 40 track ones and they could never be formatted to 
40 tracks. Whs this ever true?

[Mind you, this was the same person who tried to convince me that 
formatting the 'other side' of a single-sided disk could ruin the drive 
head, although using it asa single-sided disk would cause no damage. I 
cannot think how that could be true.]

> Then, of course, 79 was simply doubling the SA400 "standard".

I assume that;s a typo. Every time I shift 100011 left by one bit I get 
1000110, or 70...

Howeer, was there ever a 70 cylinder 5.25" drive? That is one that was 
only designed to use 70 cylinders ? I mean a raw drive, not a 
drive+controller like the HP units we're discussing.


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