> Kind of old school talking about IRQ sharing in 2012 isn't it.
Basic PC motherboard architecture hasn't changed much in the last 15+ years because they want to maintain backwards compatibility.
What has changed is that modern motherboards have multiple USB and SATA controllers as well as onboard sound, lan, and video all sharing the same FOUR IRQ lines reserved for the PCI bus. Every pair of USB ports is a single device, so boards sporting 8 USB ports actually have 4 devices fighting for IRQs.
Even if you disable the LPT (parallel) port, COM (serial) ports, floppy drive, and PS/2 keyboard and mouse, no additional IRQs are available for devices sharing the PCI bus. It's still limited to 4 IRQs total even if they shift around.
I know that some modern chipsets have moved certain devices like the LAN port off the PCI bus, but I don't know how that meshes with legacy device IRQs. It probably just steals one of the PCI IRQs, leaving only three.
I think this mess is part of the reason that there was such a hard push to move to an interface like USB where multiple low-bandwidth devices can be chained off a single port using a hub architecture.
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