the silicon difference between -04 and -20 midrange parts

[asmboy]

Does anybody know the REAL difference between the 16f877-04 and
the -20 ( or -10 part for that matter )?

I have a design that works well in production that uses a 4.9 mhz ext oscillator with the -04 part - never a failure - never a problem. - I tried it today with a 7.3728 mhz osc , in an attempt to improve to proc cycles available during INTS at 76800 baud - and found that supply current to the pic increased by about 15 % but the design still worked ok.

I have not tried to push further than that but wonder if anybody knows the basis for that grading on the PIC parts.

[PCM programmer]

The difference is that if you use a -20 part at 7 MHz in a product and
it fails, Microchip tech support will listen to you.

If you use a -04 part at 7 MHz they will do this:

It's insurance.

But see these comments by Ttelmah.
http://www.ccsinfo.com/forum/viewtopic.php?t=34111