Yet another idea for recovering the data from Series80 tapes

[Tony Duell]

> Unfortunately the read/write IC (1820-2418) on the HP-85 can only deal with
> one head at a time (only one DIO pin), so to employ the one-pass strategy,
> you either have to wire another 1820-2418 strapped to read track two, or you
> have do the analog (audio) recording I suggested initially.

The latter is probably easier.

> 
> > They DO use the same tape so they must be compatible. I don't know about
> > the track spacing but I would think they would be the same.
> 
> Bad news. I checked the specs (TechData brochures from hpmuseum.net)
> and came up with this table for read/write speeds
>         HP 9825 22ips
>         HP 9835 22ips
>         HP 9845 22ips (didn't find any data, but I assume its 22 ips)
>         HP 85   11ips
>         HP 9815 10ips
> 
> So there goes any hope of cassette data interchange between the Series80
> and the rest of the HP line. :-(

Nonsense. You cannot deduce that if the tape speed is different then the 
tapes are not compatible. If you double the tape speed _and_ double the 
data rate, then the actual flux transitions on the tape are identical 
(much the same as doubling the rotational speed of a floppy disk and 
doubling the data rate there -- HP's old 3.5" drives (acutally Sony 
mechanisms) turned at 600rpm, but the disks are comapatible, read and 
write, with 300 rpm PC drives).

> My advice is to go for 9915As I have seen them go for next to nothing on eBay,
> and even then remain unsold. Apparently people do not realize that these are
> Series 80, or they are discouraged by the lack of screen and (most importantly)
> keyboard!

The monitor is trivial, of course. And the keyboard shouldn't be a 
problem now that the matrix layout (same as an 85) and connector pinout 
are available.

> PS I found another metric screw up:
> In the 9835TechData-5953-0982-12pages-Oct78.pdf file in hpmuseum.net
> the length of the tape is given as 426.7 METERS, followed by the

Presumably 42.67m

> more reasonable 140ft (the HP-85B spec sheet gives the length of tape
> as 43m or 140ft).

-tony