DDK Glossary - I

I-beam pointer: A pointer that indicates an area, such as an entry field in which text can be edited.

I/O operation: An input operation to, or output operation from a device attached to a computer.

icon: In SAA Advanced Common User Access architecture, a graphical representation of an object, consisting of an image, image background, and a label. Icons can represent items (such as a document file) that the user wants to work on, and actions that the user wants to perform. In the Presentation Manager, icons are used for data objects, system actions, and minimized programs.

icon area: In the Presentation Manager, the area at the bottom of the screen that is normally used to display the icons for minimized programs.

IDC: Inter-device-driver communication. A mechanism that enables a physical device driver to communicate with another physical device driver.

image font: A set of symbols, each of which is described in a rectangular array of pels. Some of the pels in the array are set to produce the image of one of the symbols. Contrast with outline font.

implied metaclass: Subclassing the metaclass of a parent class without a separate CSC for the resultant metaclass.

in-memory buffer: A block of memory in the address space of the host machine, used for data transfer.

indirect manipulation: Interaction with an object through choices and controls.

information device context: A logical description of a data destination other than the screen (for example, a printer or plotter), but where no output will occur. Its purpose is to satisfy queries. See also device context.

information panel: A defined panel type characterized by a body containing only protected information.

Information Presentation Facility (IPF): A facility provided by the OS/2 operating system, by which application developers can produce online documentation and context-sensitive online help panels for their applications. Abbreviated as IPF.

inheritance: The technique of specifying the shape and behavior of one class (called a subclass) as incremental differences from another class (called the parent class or superclass). The subclass inherits the superclass' state representation and methods, and can provide additional data elements and methods. The subclass also can provide new functions with the same method names used by the superclass. Such a subclass method is said to override the superclass method, and will be selected automatically by method resolution on subclass instances. An overriding method can elect to call upon the superclass' method as part of its own implementation.

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, requesting a function of the device driver. Abbreviated as IOCtl.

Input/Output Privilege Level (IOPL): Allows part of a Ring 3 application or device driver to execute at Ring 0. Abbreviated as IOPL.

input focus: (1) The area of a window where user interaction is possible using an input device, such as a mouse or the keyboard.; (2) The position in the active window where a user's normal interaction with the keyboard will appear.

input router: An internal OS/2 process that removes messages from the system queue.

installable file system (IFS): A file system in which software is installed when the operating system is started.

instance: (Or object instance). A specific object, as distinguished from the abstract definition of an object referred to as its class.

instruction pointer: In System/38, a pointer that provides addressability for a machine interface instruction in a program.

integer atom: An atom that represents a predefined system constant and carries no storage overhead. For example, names of window classes provided by Presentation Manager are expressed as integer atoms.

interactive graphics: Graphics that can be moved or manipulated by a user at a terminal.

interactive program: (1) A program that is running (active) and is ready to receive (or is receiving) input from a user. (2) A running program that can receive input from the keyboard or another input device. Compare with active program and contrast with noninteractive program. Also known as a foreground program.

interchange file: A file containing data that can be sent from one Presentation Manager interface application to another.

inter-device-driver communication (IDC): A mechanism that enables a physical device driver to communicate with another physical device driver.

Interface Definition Language (IDL): Language-neutral interface specification for a SOM class. Abbreviated as IDL.

interpreter: A program that translates and executes each instruction of a high-level programming language before it translates and executes.

interprocess communication (IPC): In the OS/2 operating system, the exchange of information between processes or threads through semaphores, pipes, queues, and shared memory. Abbreviated as IPC.

interval timer: (1) A timer that provides program interruptions on a program-controlled basis. (2) An electronic counter that counts intervals of time under program control.

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.

IOPL code segment: An IOPL executable section of programming code that enables an application to directly manipulate hardware interrupts and ports without replacing the device driver. See also privilege level.

IORB: Input/Output Request Block. 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.

IPF compiler: A text compiler that interprets tags in a source file and converts the information into the specified format.

IPF tag language: A markup language that provides the instructions for displaying online information.