I

    IDC -
      Inter-device-driver communication.
    in-memory buffer -
      A block of memory in the address space of the host machine, used for data transfer.
    init time -
      See initialization time, device driver.
    initialization time, device driver -
      After the OS/2 loads a device driver, it sends it an OS/2 request packet to initialize. During this initialization, certain DevHlp functions are not permitted. Also called init time.
    Input/Output Control (IOCtl) -
      A system service that provides a way for an application to send device-specific control commands to a device driver.
    Input/Output Privilege Level (IOPL) -
      Allows part of a Ring 3 application or device driver to execute at Ring 0.
    input router -
      OS/2 internal process that removes messages from the system queue.
    inter-device-driver communication (IDC) -
      A mechanism that enables a physical device driver to communicate with another physical device driver.
    interprocess communication -
      In the OS/2 operating system, the exchange of information between processes or threads through semaphores, queues, and shared memory.
    interrupt -
      An instruction that directs the microprocessor to suspend what it is doing and run a specified routine. When the routine is complete, the microprocessor resumes its original work. See also routine.
    interrupt request (IR) -
      Broadly, an "interrupt request level", referring to pending or in-service interrupt requests, or to a specific level (for example, IR 4).
    interrupt request flag -
      A bit in the 8259 PIC controller that indicates an interrupt is pending on particular level. The VPIC also maintains a virtual interrupt request flag for each interrupt level for each DOS session.
    interrupt service flag -
      A bit in the 8259 PIC controller that indicates an interrupt request is being serviced. It is cleared when the PIC is sent EOI. The VPIC maintains a virtual interrupt service flag indicating that a simulated interrupt is in-progress in a DOS session.
    interrupt time -
      When a device driver is run because of an interrupt rather than because of an application request. OS/2 device drivers receive interrupts either from the hardware they manage or from the system real-time clock.

      During interrupt time, certain DevHlp functions are not permitted. Also, addresses received directly from OS/2 applications might not be valid unless they are converted system addresses.

    IOCtl -
      Input/Output Control.
    IOPL -
      Input/Output Privilege Level.
    IORB -
      Input/Output Request Block.
    Input/Output Request Block (IORB) -
      A data structure defined by this specification that is passed as a parameter on all calls to an adapter device driver. It contains a fixed section, followed by a command-dependent section.
    IORBH -
      Input/Output Request Block Header
    IRET -
      Interrupt return.
    IRQ -
      Interrupt Request.

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