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COM1, come all

Plus, should fans push or pull cool air?

Q: I finally need to use the COM1 port on my PC for a replacement mouse, but the port isn’t working. How can I check the port or get it working?

A: There are many possible issues preventing your COM port from working, but most points are easy to check. Always start by checking the CMOS Setup (usually in an Advanced or Integrated Peripherals submenu). Locate the entries for your serial ports 1 and 2, then verify that the ports are assigned to an IRQ and I/O address.

If one or both ports are disabled, the serial device won’t work on that port, and you’ll need to enable the desired port(s) through the CMOS Setup routine. Save your changes and reboot the system normally.

Now check the Device Manager in your version of Windows. Expand the Ports (COM & LPT) entry and check for both Communications Ports (COM 1) and (COM 2). Once the ports are enabled on the motherboard, Windows should recognize and install the port(s). If not, you may need to refresh the device list, or try the Add New Hardware wizard to install the COM port(s) yourself.

The Device Manager may indicate a conflict between your COM port and another device in the system. For example, you may not be able to use COM1 if your PC uses an internal modem set to use COM1 resources. This causes a hardware conflict. You can resolve the conflict by assigning different resources to the conflicting device, or removing the conflicting device (at least temporarily).

Finally, check for cabling problems. Some older motherboards use a small cable to connect a header on the motherboard to ports located on an expansion card bracket. In many cases, this small cable is specific to your particular motherboard. Be sure that the cable is attached securely (and in the proper orientation), and verify that it’s the correct cable for your motherboard. You may need to contact the motherboard manufacturer for an appropriate cable. If the problem persists, the motherboard may be defective and require replacement.

Q: I’m upgrading my ATX power supply, and I notice that the fan exhausts air rather than takes air in (as the previous power supply did). Is there a preference in fan direction for the power supply, and will the direction affect system cooling?

A: There has always been a bit of debate regarding fan direction, and the ATX specification allows several different configurations for fan location, direction, speed, and vent locations. These variables allow cooling to be tailored to specific system applications. Version 1.1 of the ATX/ATX12V design guide specifies that air be exhausted from the enclosure through a power supply fan (operating at 25-35CFM) located at the exterior panel of the supply, so your new power supply meets the preference for air direction.

In practice, critical devices in the system (namely the CPU and major graphics coprocessor chip) are cooled with their own heat sink/fan units, so the choice of air direction has little effect on overall cooling for average PC builders.

Q: I had 32MB of RAM, then added a PC100 128MB DIMM, but only 96MB of RAM is reported by the BIOS. The manual said a PC100 128MB DIMM is fine. Is the new DIMM damaged, or did I miss a step during installation?

A: It sounds like the system is only recognizing half of the new 128MB DIMM (64MB + 32MB = 96MB). A BIOS issue may cause this type of trouble, so contact the PC maker to see if a BIOS upgrade is available. This might correct this problem.

Also, the larger DIMM may need to be in the first slot, so remove the older 32MB DIMM and insert the new 128MB DIMM into the first DIMM slot. If the system boots and recognizes the full 128MB, power down again and try the 32MB DIMM in the second slot.

If the system refuses to recognize the entire 128MB DIMM (even after a BIOS upgrade), the new memory module’s chip density may simply be too high for the chipset on your motherboard. Check the motherboard manual or consult with the system maker to determine the range of memory chip densities supported by the motherboard (not all manuals will list chip densities as a specification), then check that against the chip density used on the new DIMM.

You may need to return the 128MB DIMM and exchange it with another 128MB module using slightly lower-density RAM chips (i.e. 128Mbit chips rather than 256Mbit chips). If the new DIMM is appropriate for your system, but the problem persists, try another PC100 128MB DIMM.

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