IRQ DMA I/O Addresses

Discussion in 'A+ Certification' started by Stephen Online©, Jun 11, 2004.

  1. A couple questions:

    IRQs and DMA channels and I/O address are all ways for devices to 'talk'
    with the CPU. Are any of these dependant on the other? In other words, is
    there are a relationship between them or are they completely autonomous
    systems?

    Also .. my system goes up to at least IRQ 23 but the books and websites say
    IRQs go up to 15. What gives?

    Thanks.
    Stephen Online©, Jun 11, 2004
    #1
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  2. Stephen Online©

    Mark Guest

    Newer OS's will create virtual IRQ's.

    --
    Mark
    MCSA, CNA, A+, Net+, iNet+, Server+
    "Stephen Online©" <> wrote in message
    news:Gkjyc.3859$...
    > A couple questions:
    >
    > IRQs and DMA channels and I/O address are all ways for devices to 'talk'
    > with the CPU. Are any of these dependant on the other? In other words, is
    > there are a relationship between them or are they completely autonomous
    > systems?
    >
    > Also .. my system goes up to at least IRQ 23 but the books and websites

    say
    > IRQs go up to 15. What gives?
    >
    > Thanks.
    >
    >
    Mark, Jun 11, 2004
    #2
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  3. Stephen Online©

    A Guest

    Hi Stephen,

    I just passed the Core exam and am about to take the OS exam.

    You need to know and understand the following:

    The CPU talks to all devices through I/O memory addresses.
    All devices that need to interrupt the CPU have an IRQ.
    DMA Direct memory access does not involve the CPU. The floppy drive uses DMA
    channel 2 and can transfer data for example to the hard drive directly and
    not through the CPU, leaving the CPU to get on with other stuff.
    Lastly regarding IRQs: very old PCs only had 8 which was a nightmare when
    adding ISA cards. No two devices may have the same IRQ unless they are
    devices that never talk at the same time. Modern PCs have a second IRQ
    controller giving another 8 IRQs. It is chained to IRQ2 so IRQ2 and 9 are
    the same. PCs made in the last few years completely ignore the rules by
    creating IRQ channels. You will see "faked" IRQ numbers such as IRQ23. Its
    done for backwards compatibility with any older programs or devices that
    need a "real" IRQ. For A+ you should memorise IRQs 0 to 15. IRQ0 is the
    system timer. There are 16 IRQs less one because 2 and 9 are the same, so in
    total only 15.

    Hope that helps a bit.

    "Stephen Online©" <> wrote in message
    news:Gkjyc.3859$...
    > A couple questions:
    >
    > IRQs and DMA channels and I/O address are all ways for devices to 'talk'
    > with the CPU. Are any of these dependant on the other? In other words, is
    > there are a relationship between them or are they completely autonomous
    > systems?
    >
    > Also .. my system goes up to at least IRQ 23 but the books and websites

    say
    > IRQs go up to 15. What gives?
    >
    > Thanks.
    >
    >
    A, Jun 11, 2004
    #3
  4. Thanks to everyone who replied.
    Stephen Online©, Jun 12, 2004
    #4
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