3 ms·
The bits don't have "start of bit" nor "end of bit" marks. The only way the reader can know which impulse constitutes a bit is by timing.
by praptak 17y ago
The bits don't have "start of bit" nor "end of bit" marks. The only way the reader can know which impulse constitutes a bit is by timing.
- prewett 17y agoThere are a lot of credit card machines where the purchases swipes the card themselves. Since the speed that people swipe is going to be variable, it can't be too hard to read a card without knowing the speed. (Like, say, putting 10101010 at the beginning, which you could use for calibration) So I'm not sure how a random speed helps things. Maybe ATM bits aren't encoded like credit cards?
- praptak 17y ago"Since the speed that people swipe is going to be variable, it can't be too hard to read a card without knowing the speed." The speed just has to be fairly constant within a single swipe - then you can adjust for it. It usually is when humans do that - human hand has quite an inertia. The security feature on ATMs makes it vary wildly within a single swipe.