I have a Win2K system that I'm trying to setup the com ports for. I know com port 1 should have IRQ 4, but can figure out what com port 3 should be. My main modem is on com port 1 and I'm installing a wireless modem to com port 3. I appreciate any help and/or ideas.

COM3 shares IRQ4 with COM1, they have different I/O adresses: COM1 IRQ4 3F8-3FF COM2 IRQ3 2F8-2FF COM3 IRQ4 3E8-3EF COM4 IRQ3 2E8-2EF That's all.

New Guy, I'm assuming that your main modem is internal. If so, is it a PCI modem or an older ISA modem? If it's a legacy ISA modem, you may not be able to use your PC's 2nd serial port. This is because "legacy" hardware devices don't usually support IRQ sharing. If this is the case, you'll need to replace your modem with a newer PCI modem in order to to enable your PC's second COM port. When you power up your machine, go into the BIOS setup screen and look at your COM port settings. Depending on how old your PC is, you may be limited in the possible IRQ and I/O settings for these devices. You don't want the BIOS IRQ settings to conflict with any legacy or non plug-n-play cards. Again, if this is not possible - you'll need to get a newer PCI modem. The IRQ's and addresses for COMX that Peter gave generally refer to older versions of DOS and Windows and don't necessarily have to be used. PCI modems and COM port cards have port drivers that support IRQ's other than 3 & 4. The only time you need to worry about those "legacy" port assignments, is with older Windows or DOS programs that have these COM port settings hard-coded. Windows 2000 programs don't care about IRQ assignments because this is handled by the kernel and device drivers. Hope this helps. - John

I have the same problem. Could you tell me why WIN 2000 can not share IRQ on COM ports. I have ISA modem with jumper seting on COM3. With WIN 98 both COM ports COM1 and COM3 worked without problems, but WIN 2000 can not find COM3 or if I setting up manual, than show "SHARING VIOLATION". Thanks.

Kiki, Older version of Windows weren't as strict about hardware conficts - especially with non plug & play devices. Normally, when you have an ISA modem that only supports IRQ 3 or 4, you must disable one of your PC's built in COM ports to free up IRQ 3 or 4 for your modem. Newer ISA or PCI plug & play modems allow IRQ's other than 3 & 4 so you could keep both internal COM ports enabled as long as there are no conflicts. While IRQ's can occasionally be shared successfully, even with legacy hardware, if you attempt to access them at the same time, you'll run into problems. Only newer PCs with APCI BIOS, PCI cards and operating systems that support this hardware can truly share IRQ's without conficts. Windows 2000 wants total control of hardware - something that older versions didn't enforce. It's what makes Win2K more stable because software can't directly access hardware and cause crashes or lockups. Older DOS and Windows applications would often bypass the OS and communicate directly with COM ports, which is why they don't always work under Win2K. The fact that Win2K is not allowing your legacy devices to share IRQs is a good thing since doing so can cause problems. You may have had COM ports that shared IRQ's under Win98, but I doubt you were able to use both ports simultaneously. The whole issue of COM1=IRQ4, COM2=IRQ3, etc really goes back to the DOS and the original IBM PC architecture. It's only still there for backward compatibility. You're better off with phasing out legacy cards and going with 100% PCI cards that generally rely on bus mastering instead of IRQs. Many of the new PC's don't even have ISA sockets available. Eventually, the operating systems will stop supporting them altogether. I'm not knocking legacy devices - I'm a 100% geek who is very comfortable with dip switches and jumpers - but I can't tell you how many all-nighters I've pulled trying to make all that stuff work. - John

I set all 4 com ports with the above settings, but it still won't find the modem. It's a PCI modem (Hayes Accura 144B + 144F). I use to have the internal modem working on com port 1 and an external modem working on com port 3 before I reimaged the computer (I knew I should have copied those darn settings). Com ports 3 and 4 both have the exclamation point in the device manager with error code 10 (the device cannot start). I also checked the BIOS for com ports and set it to AUTO. Should I keep it as AUTO, or should I put it as something definite? I appreciate the help.

New Guy, Instead of AUTO, for grins, try assign the correct IRQs to your COM ports in the BIOS setup. Does the internal PCI modem HAVE to be on COM1? I would use COM3 or COM4 for the internal modem and set the motherboard's COM ports to their defaults (COM1-IRQ4, COM2-IRQ3). Your PCI modem should support IRQ sharing, so it should be able to use somthing other than IRQ3 or IRQ4. I have a 3Com 56K PCI modem that's using IRQ 9, even though it shows up on COM2. Again, COM2=IRQ3 is a legacy rule for old hardware and OS's. It's really just a logical device name in Win2K. Your BIOS setup should allow you to force IRQ assignments on each PCI slot. I have them all set to AUTO and for the most part, all of my PCI cards are sharing IRQ 9 with NO problems. The sticky issue is those motherboard-based COM ports. Even though they are technically attached to the PCI bus, Windows still considers them legacy (ISA) devices - so it's best to set them up to their defaults and let your PCI cards share the free IRQs. Go into Control Panel, System, Hardware, Device manager and select View, Resources by connection. This is a good way to check how all the IRQs are assigned. If your system BIOS is set for Plug & Play, I would turn that off. Enabling Plug & Play lets the BIOS handle the PCI IRQ assignements instead of Windows. Hope this helps. - John