.cab file

See cabinet file.

cabinet file

A "cabinet" of compressed installation files, with a file extension of .cab.


A special memory subsystem in which frequently used data values are duplicated for quick access. Cache memory is always faster than RAM.

Cache Manager

A system component that provides file caching support for file system drivers.

call management

The process used to set up and tear down calls. The call management process also controls the operational parameters of the call. The term "call," and therefore "call management," describes processes that refer to a higher level of call control, rather than those processes responsible for the physical connection.


See common access method (CAM).

Card Services

Under Windows 95, a protected-mode system component that is a VxD linked with the PCMCIA bus driver. Card Services passes the event notification from socket services to the PCMCIA bus driver, provides information from the computer's cards to the PCMCIA bus driver, and sets up the configuration for cards in the adapter sockets.


See closed captioning (CC).


See context control block (CCB).


See Consultative Committee for International Telephone and Telegraph (CCITT).


See command descriptor block (CDB).


See compact disc file system (CDFS).

character translation table (CTT)

Used in print minidrivers that are created for NT-based operating systems. CTTs are translated to RLE bitmaps files.


To follow a linked list, queue, or other software-defined path. For example, when a file system encounters a symbolic link file within a path specification, it "chases the symbolic link" to redirect operations to the target file.

See also symbolic link.

checked build

A version of the system that has been compiled with debug symbols and built with special support for debugging under-development components, such as new drivers. For more information, see the topic Checked and Free Build Differences.

See also free build.

child partition

Within the hypervisor, a host to a guest operating system.

child process

When a new NT-native process is created by calling a system service, the caller must specify a "parent" process from which the new process inherits its token, quota, and base run-time priority for threads. The new process can optionally inherit any or all of the following from the specified parent process:

  • A copy of the parent's virtual address space
  • All object handles that were opened with the inheritance attribute
  • Debugging and exception handling ports

However, any user-mode process becomes a wholly independent peer to its so-called parent process as soon as it has been created. After process creation, any process-to-process dependencies become the responsibility of a protected subsystem, such as the Win32 or POSIX subsystem.

A kernel-mode-only process has the initial system process as its parent.

chroma, chrominance

The color portion of the video signal that includes hue and saturation information. Requires luminance, or light intensity, to make it visible.


See client identifier (CID).


See International Commission on Illumination (CII).


See Device Setup Classes and Device Interface Classes.

class driver

A higher-level driver that typically provides hardware-independent support for a class of physical devices. A class driver generally communicates with a lower-level miniclass driver or port driver, using a combination of device I/O control requests (IOCTL), callbacks, and support routines.

The system supplies class drivers for keyboard, mouse, and storage devices, among others.

For more information, see the topic Device nodes and device stacks.

class GUID

See setup class GUID.

class installer

A Win32 DLL that performs installation operations for devices in a particular Device Setup Classes.

For more information, see the topic Writing a Class Installer.

clear to send

A control packet used by a destination station to indicate its readiness to receive data. A destination station responds to a Request To Send (RTS) by transmitting a CTS.

See also request to send (RTS).

client identifier (CID)

A unique value that identifies a thread.

client/server model

A model for structuring applications or operating systems such that the system is divided into server processes, each of which provides a set of specialized services to client processes.

clip region

A rectangle or set of rectangles used to control which portions of an image are displayed.

clip region locking

A mechanism by which GDI ensures that a clip region will not change during a drawing operation. To prevent a clip region from being changed during such operation, GDI acquires a lock for the region, thereby controlling access to the data structures that could affect clipping.

clip window

A rectangular region that is used to mask an area in a document or image. Only the portion of the document or image that lies inside the clipping region appears when the document is printed or the image is displayed.


A GDI user object that describes the clip region used when drawing. This region can be enumerated as a series of rectangles.

closed captioning (CC)

A service that transmits text captions for a television program and can be displayed on any modern television with a display size measuring greater than 13 inches (33 cm) diagonally. CC usually consists of text that describes the audio program of a show and is typically defined by EIA standards 608-1994, 708-B, and 744. Multiple channels and languages are possible, with CC1 carrying the primary language of the program and CC2 carrying the alternate language. For example, if a news program's audio track is in English, then CC1 would carry captions in English. If Spanish captions were available, they would be carried on CC2.


The color space that is often implemented on printers. The acronym represents the four colors: cyan, magenta, yellow, and black.


Coder-decoder. A filter that compresses or decompresses a data stream.


A co-installer is a Microsoft Win32 DLL that augments the device installation operations performed by a class installer.

Co-installers can be class-specific (class co-installers) or device-specific (device co-installers).

For more information, see the topic Writing a Co-installer.

cold docking

Inserting a portable computer or other mobile system into a base unit while the mobile system's power is off.

collided page fault

A page fault caused by one thread while an in-page I/O operation for another thread is being performed on the same page.

color index

An index into an array of RGB values.

color keying

The process of superimposing one image over another for special effects.

  1. The Component Object Model; the core of OLE. COM defines how OLE objects and their clients interact within processes or across process boundaries.
  2. A legacy serial port.
command descriptor block (CDB)

A structure defined by the SCSI-II standard and used to communicate requests to a target device on a SCSI bus.

commit charge

The number of virtual memory pages that have been assigned (committed) to physical memory or a paging file.

See also current commit limit and maximum commit limit.


The memory manager's current system-wide total of memory pages that has been committed to either physical memory or a page file.

common access method (CAM)

An interface definition for SCSI devices.

Common Property Sheet User Interface (CPSUI)

A user-mode dynamic-link library that enables developers to create property sheet pages that have a standard appearance.

compact disc file system (CDFS)

Controls access to the contents of CD-ROM drives.

compatibility mode

An asynchronous, host-to-peripheral parallel port channel defined in the IEEE 1284−1944 standard. Compatible with existing peripherals that attach to the Centronics-style PC parallel port.

compatible ID

A vendor-defined identification string that Setup uses to match a device to an INF file. Setup uses compatible IDs if it cannot match the device ID and hardware ID for a device.

For more information see the topic, Device Identification Strings.

See also instance ID and device instance ID.


In DirectX Video Acceleration, one of three color channels {Y, Cb, Cr }.

component prediction block

In DirectX Video Acceleration, a prediction block whose attributes apply to either one of luminance or chrominance.

composite prediction block

In DirectX Video Acceleration, a prediction block whose attributes apply to both luminance and chrominance.

composite video

A signal that combines the luminance, chrominance, and synchronized video information onto a single line. This has been the most prevalent NTSC video format.

compressed video

A digital video image or segment that has been processed to reduce the amount of data required to accurately represent the content.

Consultative Committee for International Telephone and Telegraph (CCITT)

An international standards organization dedicated to creating communications protocols that enable global compatibility for the transmission of voice, data, and video across all computing and telecommunications equipment.


The execution state of a thread at any given moment:

  • For a user-mode thread, the platform-dependent register state, kernel stack, TEB, and user stack in the address space of the process to which the thread belongs.
  • For a kernel-mode thread, the platform-dependent register state and kernel stack.

Kernel-mode threads have neither a TEB nor a user-mode context, but they must have an associated process.

Most kernel-mode drivers do not have a context in this sense. Unless a driver (such as an FSD) creates its own process and/or thread(s), it does not have its own stack space or register state. For each driver, the set of objects it owns and the IRPs that it can access in the device queue associated with its device object or any driver-created internal queue(s) can be considered all or part of its context.

See also process object.

context control block (CCB)

An internal file system structure, in which a file system maintains the per-file object state for an open instance of a file.

See also file control block (FCB) and directory control block (DCB).

context record

A system-defined structure that contains the current register state for an exception handler.

See also structured exception handling.


The range of light and dark values in a picture; or a measure of brightness in an image. The range between the lightest tones and the darkest tones in an image.

control method

A definition of how an ACPI-compatible operating system can perform a simple hardware task. For example, the operating system invokes control methods to read the temperature of a thermal zone. Control methods are written in an encoded language called AML. An ACPI-compatible system must provide a minimal set of control methods in the ACPI tables. The operating system provides a set of well-defined control methods that ACPI table developers can reference in their control methods.

control objects

A class of kernel-defined object types, used to manage all kernel-mode operations except dispatching and synchronization.

Control objects include APC, DPC, device queue, interrupt, and process objects. Note that all control object types except processes are kernel-mode-only objects, invisible to user-mode code. User-mode APC objects are also "invisible" in the sense that they look more like user-supplied routines to be called on return from certain system services (such as a request to read a file) than like objects.

See also dispatcher objects.

controller object

A kernel-mode-only object type, defined by the I/O manager. A controller object represents a hardware controller or channel. The driver calls the IoAllocateController function to carry out synchronized I/O on attached devices. Controller objects "connect" a set of similar devices attached to a controller with a single driver.

controllerless modem

A modem that consists of a DSP without the usual microcontroller. The host CPU provides the AT command interpreter, modem-control functions, and v.42bis implementation. Also called a host-based controller.

Compare with software modem.

CPUID leaf

An input value to the CPUID instruction; the CPUID instruction then returns four registers of information (EAX through EDX). Or, an index into information that is defined by a processor manufacturer or virtualization provider.

critical section

A piece of code that temporarily has exclusive access to a resource, such as device-state data stored in a device extension to which access must be synchronized among some number of routines.


Connection and Streaming Architecture. Kernel-mode streaming in WDM.


See clear to send.

current commit limit

The maximum number of virtual memory pages that can be assigned to physical memory or a paging file without enlarging a paging file.

See also commit charge and maximum commit limit.



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