About time spent have big difference in two running

G

Guy Macon

Just for reference:

Assuming a stock IBM PC without the counter reprogrammed,
the "18.2 per second" interrupt was derived as follows:

The IBM PC Clock Crystal oscillates at 4770000 Hertz.
4770000 / 4 / 65536 = 18.19610595703125 Hertz.

This is close to 65536 ticks per hour:
3600 Seconds (1 Hour) / 65536 = 18.20444... Hertz.

And is related to a NTSC Color Crystal at 14318180 Hertz:
14318180 / 12 / 65536 = 18.2065073649088541666... Hertz.

That 4770000 Hertz IBM PC Crystal had a best case accuracy
of +/- 0.0005%, a typical accuracy of +/- 0.002%, and a
worst case accuracy of +/- 0.01%. Some servers have oven
stabilized crystals with an accuracy approaching 0.00001%
(0.1 ppm).

Also, There is a list of interrupts and IRQs here:
http://docs.huihoo.com/help-pc/int-int_table.html
 

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