Interrupt
IBM PC Assigns This Interrupt To:
IRQ2/9
2 NOT available in Windows 95. 9 sometimes available.
IRQ3
COM2: Second Serial Port, sometimes available
IRQ4
COM1: First Serial Port
IRQ5
LPT2: Second Parallel Printer Port, usually available
IRQ6
Floppy Disk Controller
IRQ7
LPT1: 1st Parallel Printer Port
IRQ8
Real Time Clock
IRQ10
Available
IRQ11
Available
IRQ12
Pointing Device (Mouse)
IRQ13
Math Co-processor
IRQ14
Hard Disk
IRQ15
Second Hard Disk, usually available
Typical IRQ Assignments in the PC
Plug-and-Play (PnP) and Resources
Before PnP, properly configuring a PC compatible system was no small
task. Usually when new devices were added to the system, the hardware
was manually configured with jumper blocks and DIP switches, and
there were configuration conflicts that caused the computer to work
erratically or not at all. Users typically resolved configuration conflicts
by consulting complicated documentation provided with the each inter-
face card, contacting the supplier's technical support group, consulting a
friend, or giving up in disgust. Even trained engineers found the PC
card configuration process unreliable and frustrating. As the current
generation ISA expansion cards were introduced, including multi-func-
tion versions with wavetable music synthesis, hi-fidelity audio, MPEG
audio/video & FAX/modem capabilities, more systems resources were
required than ever before, causing even more system resource conflicts.
In 1993, the first PC PnP specification was proposed as a solution to com-
mon resource conflicts. PnP defines a means for the computer to com-
municate with its various installed devices and resolve any potential
resource conflicts. In theory, with a working PnP system, jumpers and
DIP switches are a thing of the past and compliant hardware is config-
ured automatically or with little user intervention. PnP works with exist-
ing bus architectures and is widely supported by the industry. To gain
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