## Virtual Device Driver Reference for OS/2

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### BIOS Hardware Interrupt Support

In previous versions of the OS/2 operating system, DOS applications were prevented from hooking hardware interrupts when the IRQ level was owned by an OS/2 device driver. A DOS application that violated this rule was terminated. In the current version of OS/2 this restriction is significantly relaxed. Depending on the support provided by the device's virtual device driver, DOS applications can now hook the hardware interrupt vector. The following list summarizes the support provided by OS/2 virtual device drivers for each of the hardware interrupt request (IRQ) levels:

IRQ 0 Timer (INT 08h). The INT 08h handler is invoked on hardware interrupts from Channel 0 of the system timer. DOS applications can hook this interrupt. See the description of INT 08h in BIOS Software Interrupt Support.

IRQ 1 Keyboard (INT 09h). The INT 09h handler is invoked upon the make or break of every keystroke. DOS applications can hook this interrupt.

IRQ 2 The Cascade (Slave) Interrupt Controller. This controller supports interrupt request levels 8 through 15, as described below.

IRQ 3 Serial Ports (COM2, 3, 4). These ports are supported when the virtual and physical COM device drivers are installed.

IRQ 4 Serial Port (COM1). This port is supported when the virtual and physical COM device drivers are installed.

IRQ 5 Parallel Port 2. This hardware interrupt is simulated in DOS sessions .

IRQ 6 Diskette. This hardware interrupt is not simulated in DOS sessions. See the description of INT 0Eh in BIOS Software Interrupt Support.

IRQ 7 Parallel Port 1. This hardware interrupt is simulated in DOS sessions .

IRQ 8 Real-Time Clock. This hardware interrupt is not simulated in DOS sessions. See the description of INT 70h in BIOS Software Interrupt Support .

IRQ 9 Redirect Cascade. A virtual device driver to simulate this hardware interrupt is not provided.

IRQ 10 Reserved. A virtual device driver to simulate this hardware interrupt is not provided. See Reserved IRQ Support in OS/2 for more information.

IRQ 11 Reserved. A virtual device driver to simulate this hardware interrupt is not provided. See Reserved IRQ Support in OS/2 for further information.

IRQ 12 Auxiliary Device. A virtual device driver to simulate this hardware interrupt is not provided. See Reserved IRQ Support in OS/2 for further information.

IRQ 13 Mathematics Coprocessor (NPX). NPX exception interrupts on IRQ 13 are reflected into the DOS session.

IRQ 14 Fixed Disk. This hardware interrupt is not simulated in DOS sessions .

IRQ 15 Reserved. A virtual device driver to simulate this hardware interrupt is not provided. See Reserved IRQ Support in OS/2 below for more information.