never having seen one, I didn't think it was that literally a
    "one-time" device.  Always thought it would be windowed.  Interesting.

Yeah.  Someone (it might even have been microchip) noticed that the package
for their UV-erasable micros was getting to be a lot more expensive (since
it's ceramic, and has that glass/quartz window) than the chip itself.  In a
normal package, you can only program it once, but turnaround is a lot
quicker than a mask-programmed part, which is a BIG advantage.  You can
also start using packages that you could never fit a window in (SOIC, etc.)

Since then, everyone has been doing it, even for things like real EPROMS,
for similar reasons.  (I guess the other big reason is that the other OTP
technologies (fuses) never came close to matching the density improvements
of EPROM technology.  (Atmel even seems to be offering some OTP devices
based on FLASH technology, which is ... interesting, I guess.)

You don't see as many "hobbyist" programmers for the OTP/UV PICs because
they tend to be more complicated parallel algorithms...

BillW

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