Computer IRQ

I recently came across some IRQ information that baffled me and I wondered if someone can help.

As I have known for sometime there are 16 IRQ’s on a system (0-15); however, I just came a accross a Compaq system that has more listed. The SoundMAX Ingegrated Audio IRQ is listed as 17.Can you tell me how they were able to achieve this feat???

Thanks
Petadove