I have to be careful not to get on my soapbox about what IBM did to us in
their original PC design! However, here is an attempt to explain the basics
of the COM ports.

Although there are extensions to this, a standard PC configuration allows
for two serial ports to be present - usually COM 1 and COM 2. COM 1 uses IRQ
4 and COM 2 uses IRQ 3. If additional ports are added, such as COM 3 or COM
4, they usually have to share the IRQ with the first two COM ports. The most
common arrangement is for COM 3 to use IRQ 4 and COM 4 to use IRQ 3. Your
motherboard will have only two COM ports (unless you have a special board)
and these will be COM 1 and COM 2. When you add an internal modem to your
computer, the modem needs to identify itself to the system as a COM port.
Generally, there are settings to select from COM 1 to COM 4 for the modem.
The IRQ is also usually configurable. If you pick COM 3 for the modem, then
it will likely use IRQ 4. The computer can differentiate between COM 1 and
COM 3 based on the I/O address, but because the IRQ values are the same, you
cannot use COM 1 and COM 3 at the same time. For example, you could not have
a mouse on COM 1 and a modem on COM 3 since the mouse would interfere with
the modem and vice versa.

The best solution is usually to disable one of the COM ports on the
motherboard and using that port for the modem. Perhaps disable COM 2 and set
the modem to be COM 2. Then there would be no interference. Some modems do
allow use of additional IRQ values such as IRQ 5. In such a case, you could
set the modem to be COM 3 with IRQ 5 and the modem would work along with the
two COM ports. Note that not all software recognizes such settings, and the
software must be configured to work with the particular IRQ for the modem.
Since modern computers rarely use COM ports except for external or internal
modems, you might as well disable a COM port to avoid any chance of modem
problems.

Here is a link to more information on the serial ports in a PC in case you
want to learn more of the history and details:
http://members.iweb.net.au/~pstorr/pcbook/book2/serial.htm

Hope this helps and does not add to any confusion.

Peter
-----------------------------------------------
The NoSpin Group
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> -----Original Message-----
> Thanks for your input.  I uninstalled COM 4 and I can now connect.
>
> I would expect since the modem is on COM 3 that COM 3 would need to be
> installed.  In laymen's terms, can you offer a brief explanation...my
> education continues.
>
> Jeff

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