Re: Cards for the HP9810 Message #7 Posted by Tony Duell (UK) on 30 July 2002, 7:11 p.m., in response to message #6 by David Smith
I am _sure_ the cards are not preformatted. The card reader hardware writes the clock track as it writes the data (same on the 9100, BTW, except that the 9100 does rather more in hardware than the 9810 does).
That's why the card speed is relatively critical for writing. If the card is fed too slowly, the bits will be written too close together, and will be unable to be read).
To digress slightly, the HP71 and HP75 cards _are_ pre-formatted -- the clock track is written at the factory. When you write on one of those cards, the card reader _reads_ the clock track to determine when to write the next bit. That's why those machines can get away with hand-pulled cards for writing. The older machines (9100, 9810, 9820 which have a clock track that's written along with the data, and the HP65, HP67, HP97, HP41, which have a self-clocking data encoding scheme) don't have a pre-written clock track, which is why you have to
have the card speed about right for writing.
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