DDK Glossary - I

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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.