On Sun, 26 Jun 2005, Aviv Goll wrote: > I don't think it's an OS issue, the fact is that you can see IRQ > allocations when you start a machine even if you don't have an OS.
this is both an OS issue, and not an OS issue. an IRQ is an 'interrupt request' number - a mechanism for a peripheral device or controller to let the CPU know that some event occured and the device needs its attention. for example - a disk controller finished servicing a disk read request. a serial (COM) port has space to accept more data form the CPU to send to its destination device (such as an old external modem), etc. in the past, device drivers assumed that a given IRQ is used only by a single device, and thus setting two devices to report events using the same IRQ caused problems. the number of IRQs available on a PC was small (around 13, with many of them pre-allocated for specific device types). also, devices were configured to use a certain IRQ by setting a jumper (a tiny piece of plastic and metal to connect two pins). further, most devices couldn't be set to all the available IRQs - they were hard-wired to support 2-4 different IRQs. when people and non-skilled ocmputer resellers messed with their own hardware, they managed to make errors often (sometimes it was not their fault - often the IRQ number was not written on the device controller, but rather in the device's booklet, which was lost, or never supplied). to solve this, there were several attempts to design data buses (the mechanism that allows the CPU, memory and the device controllers to communicate inside the computer) that can automatically manage IRQ allocation for devices. the bus type that eventually won the game was the PCI bus. however, it couldn't immediately replace the previous bus (the ISA BUS) - because then you'd not be able to use all the existing cards. so machines came with dual-busses - PCI and ISA. this means some cards were manually configured while others were automatically configured - which caused a lot of mess. in the last few years, ISA busses were completely phased out, and computers sold now don't have an ISA bus at all. in such computers, you should not have any real problems. further, because device drivers started supporting sharing the same IRQ between several devices, the problem of "too many devices, too few IRQs" is also passing away. so you should ask yourself - do you feel lucky? do you have a PCI-only computer, or still an older PC that has a dual-bus? regarding to who alloactes IRQs for the devices - i'll leave this for others to fill in, as i'm not sure about the answer, and never bothered to check. -- guy "For world domination - press 1, or dial 0, and please hold, for the creator." -- nob o. dy ================================================================= To unsubscribe, send mail to [EMAIL PROTECTED] with the word "unsubscribe" in the message body, e.g., run the command echo unsubscribe | mail [EMAIL PROTECTED]
