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Thread: Irq 9

  1. #1

    Irq 9

    All peripherals share this IRQ, yes? My question is: "Why?"

    And also, if anyone could clear up what the term 'cascade' means in relation to IRQs such as IRQ 9 cascades to IRQ2 and IRQ2 does just the opposite cascading to IRQ9.

    MySig != Worth your time

  2. #2
    Senior Member
    Join Date
    Feb 2002
    how dare you question the wisdom of microsloth's team..

    I can't claim to understand why.. other than the backwards compatibility and the structures that were present in the original IBM design.

    314068 - A General Description of IRQ Sharing in Windows XP

    252420 - General Description of IRQ Sharing in Windows 2000

    Standard IRQ, I/O Address, And DMA Assignments

    cascading is another way of saying "redirecting the IRQ's"


  3. #3
    AO French Antique News Whore
    Join Date
    Aug 2001
    This is the interrupt number that is used to cascade the second interrupt controller to the first, allowing the use of extra IRQs 8 to 15. This use as a linkage between the two interrupt controllers means that IRQ2 is no longer available for normal use. For compatibility with older cards that used IRQ2 on the original PC or XT machines (which had only one controller and a normal IRQ2 line), the motherboard of modern PCs reroutes IRQ2 to IRQ9. Hence IRQ2 can still be used but appears to the system as IRQ9. The most common cards that do this are old EGA video cards, and newer cards making IRQ2 available with the knowledge that it will be routed to IRQ9.

    More Info :
    ALL IRQ Number Info :
    -Simon \"SDK\"

  4. #4
    Thank you SDK.
    MySig != Worth your time

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