Glossary - I

 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.