41 vs 67 card reading


Hi all.

I have a 67 that has cards that are original, but may be in need of re-recording due to age related de-gaussing. I don't yet know if this is the case, but we are speaking somewhat hypothetically here. The reason I ask is that my 67 card reader is not quite functioning yet, but my 41 is working perfectly (when the batteries are fresh).

So, my question is:

As long as no non-native(i.e., 41 specific) functions are used, can a 41 card reader record the cards so that a 67 can read them? I would think that this would be the reverse to what most users do.

Appreciate any and all responses.


Hi Jim,

Unfortunately : No.

Cards written by an Hp-41C won't be readable neither an Hp-67 nor an Hp-97 even if you only use the 67' compatibility instructions.

The only way to achieve your goal is to read/rewrite them in an 67/97.




Thank you Etienne.

I am not sure of what additional header information might get written, but I was afraid that this was the case.

Ah well. Time to get the magnifying glasses and soldering iron out...


... and your wife's hair dryer to remove the calc back sticker properly!

IMNSHO, the 67 is one of the last well constructed calcs of PCE (Pre-Crap Era).

Real screws, soldered components, no petty money saving with "pressure connectors"....

Good luck, I'm sure you'll succeed!! Keep us updated!

Cheers from France!



Hi Jim,

I've ***never*** seen a HP65 or HP67 card fail due to "degaussing".
Neither I have never seen any diskette fail due to "degaussing".

And believe me - I have a lot. Including 25 year old disks and even older cards. I do even have 30 year old 8" disks that still read OK.

The physics behind this is hysteresis of the magnetic particles. It takes a certain field strength to flip them. And even if one particle is flipped by thermodynamic accident, zillions of other particles still wait for the same strong field to be flipped. The HD (high density) media used in the PC even takes much much higher fields to flip. They are almost impossible to erase of write to in old Apple II disk drives, for instance, because the magnetic flux of those drives is too low to flip them.

The bottom line is, in magnetic media there is no effect like "degaussing" - if this means flipping of magnetic domains just by ageing without strong external magnetic fields.

What really happens is that the softening agents gass out and the magnetic particles start to separate from the plastic carrier. This is not "degaussing" but "drop out".

I do have some HP65 / HP67 cards that won't read anymore, but under magnification, it is possible to see those damage spots where the magnetic particles have gone away.

The only cure is to COPY you old cards to newer cards. But do do try to "refresh" the old cards - it is futile - as long as they read OK and don't fall apart mechanically (as described above) they are good. And if they start to lose magnetic coating, well, the they are finished and no attempt to write on them will fix that.

best regards,


They are almost impossible to erase of write to in old Apple II disk drives, for instance, because the magnetic flux of those drives is too low to flip them.

I'm confused about what you're saying here. However, in my experience, I have lost data on Apple II floppies. I mistakenly put them on top of the disk drive... The next time I tried them, every one was wiped.

I don't think it was a coincidence. They were fine for years (when stored far from the drive), then they all died at once. And I know of a separate occasion where the same thing happened.

Of course, this was due to the field created by the drive, not by random thermal flipping over time.


OK, I inadvertently used the phrase "degaussing", when perhaps it appears I should have said "degassing" or drop out. I had a middle aged moment when I wrote that because I knew it wasn't right, but I knew that someone would correct me on it and then give me an answer - and thanks BTW. This continues to be one of the reasons that I hang around this board.

But, I still don't understand, all I did was hold them on the refridgerator door with little flower magnets.....

(really, truly, honestly, kidding)


I don't think it was magnetic fields from the Apple II disc drive. It would not work if it own fields would corrupt data in a disk that's inserted. Same reasoning most likely applies to disks placed on top of the drive. Maybe your diskettes catched some field from the degaussing coil of a nearby color monitor, who knows. All Apple II disc drive I know of have a metal case which should shield mag fields anyway. But in any case, none of my properly stored diskettes ever have lost data except those who decompose mechanically (literally). I do have some candidates which I don't dare to read until I have the hardware ready to capture them forever - and of course, the head will only step ONCE through the disc.



The sure fire way of erasing an Apple diskette was to put it on the Graphics Tablet.

As the bit densities of modern hard drives has increased we are approaching the limit where random thermal noise and adjacent bit flux coupling can cause bits to flip. Curses Dr. Boltzman...

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