Identifying COM ports

Ok say for example my computer has 3 com ports when i look in my device manager.
How do i tell which com port is which when i look at the back of my computer?

 

It doesn't really work that way. There may or may not be any 'actual' COM ports on the back of your PC. My Device Manager shows I have one COM port, and I think it is probably the header on my motherboard that would allow me to add a serial port or old-school parallel port, but on the back of my PC I have neither a parallel or serial port. If your motherboard has a serial port or two (a 9 pin connector that looks like a video/monitor connector but with 2 rows of pins instead of 3) that would 'count' as a COM port (or two). Dial-Up modems are usually 'counted' as a COM port, and my PC doesn't have a dial-up modem (does anyone still have a modem these days? LOL ). Parallel ports are also occasionally labeled as COM ports. But the real question is: Why are you asking? COM ports are a thing from Win95/98/Me and have more-or-less been phased out in modern PCs.

 

actually work related. your right its rare that it comes up but it does come up from time to time.

We support some systems where they use the com port to send data from one pc to another. For the life of me dont ask why they insist on using the serial cables.

Anyway we assign our software to send across COM1, COM2, COM3 or whatever.

When the question arises ,as it always does, which one is COM2 or whatever. Im always left with the response. "I dont know, just plug it into each available serial port untill it works"

 

If there's a dial-up modem, it usually assigns COM2 to itself if it's available. If not, a modem will take the next available COM port which would be COM3 (duh) by default unless it's taken, and it goes down the line until a free COM port is found. It is VERY rare to have a modem using a COM port higher than COM4, and I've only seen a modem on COM4 maybe 3 or 4 times. IIRC, COM1 is usually the serial port; it is on my PC, but I don't have an actual serial port, just a header on the motherboard to which I could plug in a 9pin ribbon cable for a serial port. Like I said above, I think parallel ports can assign themselves a COM port if needed for the hardware that's connected to it; some dial-up modems used 25pin connectors which could be routed through the parallel port as long as specialized software was installed to make the parallel port act like a serial port. I think. This stuff goes back a long time so I'm not 100%... my memory is like old swiss cheese: it stinks and is full of holes. Anyway, more info than you probably need can be found at this Wiki about serial ports.
I hope this helps!

(BTW- you should encourage your work to step into the 1990's and move past the serial connections into CAT5 or wireless data sharing)

 

ok cool thanks.

Ya we do use CAT5 and wireless but we interface with a few other systems which we dont control and some of them insist on using serial cables.

 

This will do it, if your up for the task.

http://www.sudt.com/en/ap/download.htm

 

I think your a little mistaken, COM port are serial in nature, there are 9 or 25 pin cable for external devices like a 'blaster' modem, etc. But a 25 pin 'LPT' port is parallel. Very different in data transfer. Serial is one bit after another, think marching in a single row, parallel transmit 'all' bits at once, all being like 8 bits.

But the way to identify the ports is via a loopback test....
http://www.ni.com/white-paper/3450/en
http://www.mcselec.com/index.php?option=com_content&task=view&id=165&Itemid=57