Here is a list of my Win98 IRQ assignments.  Some of them are shared.  The
interesting ones are 3,4,5,7,9,10, and 11.  The others typically can not be
changed by the dos user although in windows you can do some ugly things.
Plug and Play have done all my assignments, and this is where you run into
trouble.  Some modems claim to be plug and play but will not accept either a
shared IRQ or a non-dos IRQ,

0       System timer
1       Standard 101/102-Key or Microsoft Natural Keyboard
2       Programmable interrupt controller
3       Communications Port (COM2)
4       Communications Port (COM1)
5       PCI Ethernet DEC 21041 Based Adapter
5       IRQ Holder for PCI Steering
6       Standard Floppy Disk Controller
7       Printer Port (LPT1)
8       System CMOS/real time clock
9       Adaptec AVA-1505 SCSI Host Adapter
10      Sound Blaster AudioPCI 64V
10      Intel 82371AB/EB PCI to USB Universal Host Controller
10      IRQ Holder for PCI Steering
11      Diamond Viper V550 for Windows 98
11      IRQ Holder for PCI Steering
12      PS/2 Compatible Mouse Port
13      Numeric data processor
14      Primary IDE controller (dual fifo)
14      Intel 82371AB/EB PCI Bus Master IDE Controller
15      Secondary IDE controller (dual fifo)
15      Intel 82371AB/EB PCI Bus Master IDE Controller

COM ports are a holdover from pre- personal computer times.  IBM in its
wisdom decided to have 4 ports, but to assign IRQ 3 to COM2 and COM4, and
IRQ 4 to COM1 and COM3.  So there are no rules that say this is the way it
has to be, it was just IBM's idea.

The trick, is getting two plug and play modems to be automatically
configured in such a way that they will work.  The simplest way is to
purchase a serial communications card with two ports, configure them as 1
and 2, then connect two external modems to them.  To use internal modems,
you need to disable in cmos settings any ports that are on your motherboard,
install two cards, preferably one at a time (install it, start windows, and
install the driver, shut down, repeat).  Hopefully, plug and play will
enable both of them.  My most frequent issue, was one or both modems
complaining that a call was already in progress.  This is probably a sign
(but not a 100% certainty) that the IRQ is something the modem doesn't like.
I have seen a modem assigned to COM5 using IRQ 11. It didn't work.

By the way, if money is no object, there are modems that will handle more
than one phone line at a time.
Tom Turak


> -----Original Message-----
> Can I have more than one modem in a computer and install it
> on any empty slot?

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