H

HAL

Hardware abstraction layer. The HAL consists of hardware and device driver mechanisms that insulate applications from device-specific implementation details. If a capability requested by an application is not implemented by the current hardware, the capability is emulated by the software.

hardware blitter

A hardware component, built into the display adapter, that performs efficient blit operations.

HEL

Hardware emulation layer. The HEL provides software-based emulation of features that are not present in hardware.

HID

Human Interface Device. A USB class representing devices that enable a human to control a computer.

hit detection

See collision detection.

host

In Microsoft� DirectPlay�, a virtual player whose ID is DPID_SYSMSG. The host manages system messages and messages sent to all players in a session.

HREF

Horizontal refresh. In a video stream, the HREF is active to signal that the display is to begin a new scan line. See also VREF.

HRTF

Head-related transfer function. A mathematical representation of the effect of the listener's physiology on the pitch and timing of sounds arriving from different directions.