Found an interesting discussion about interrupt 15: https://groups.google.com/g/alt.os.development/c/9qXsgge4b6w https://groups.google.com/g/alt.os.development/

Found an interesting discussion about interrupt 15: https://groups.google.com/g/alt.os.development/c/9qXsgge4b6w https://groups.google.com/g/alt.os.development/c/9qXsgge4b6w Looks like spurious interrupts were a thing back then, and they could become more frequent with higher temperature. > He said that Intel did not specify that interrupt 15 could be called but they probably did say in the 8259 datasheet that a spurious interrupt could be triggered. (I'm pretty sure they do in the 8259A datasheet.) > This is probably the once popular spurious interrupt 15 (0xF) the default IRQ 7 handler. Apparently much activity (getting too hot?) on the 8259a (I once generated such spurious activity as a test by increasing the timer frequency - IRQ 0) causes a spurious interrupt on IRQ 7 (LPT1).