A gate descriptor is one that defines
to the hardware a means of entering code that executes at a more privileged
level of authority. Four types of gate are defined:
Call Gate
The subject of a CALL instruction.
Typically used to implement operating system and device driver application
programming interfaces (APIs). Device drivers may create Call gates dynamically
using the DosDynamicAPI facility.
Task
Gate
The subject of a call or exception where
a (hardware assisted) task switch is required.
Interrupt Gate
The
subject of a hardware or software generated interrupt. Typically an Interrupt
gate will switch execution to an interrupt handler when a device presents
an interrupt.
Trap Gate
The
subject of a trap exception. Used to handle programming errors.
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