On the back of one of our office PCs:
 

 
Anyone know what plugs into this?
 
Cheers 

Looks like a serial port.

Cereal Port.... Capton Crunch, Post Toasties.

Midee pourt?

SteveStrummerUK
 
On the back of one of our office PCs:
 

 
Anyone know what plugs into this?
 
Cheers 

I used to use those for a modem.

definitely a serial port, no longer used no doubt due to a serial killer

I still have a parallel (compression) printer.

Yeesh. How old are the systems where you work.
 
And yes... 9 pin serial port.
 
It was essentially the "jack of all trades" connection before USB became a thing (mice, printers, data transfer, breakout boxes, etc).
 
However it may be a proprietary connector that is just disguising itself as a serial port. Sometimes manufacturers will wire up the 9 pins in funky ways to do a specific task. It does have what I THINK (IIRC) the standard serial port symbol above it.
 
They may have been added to the machines simply to be able to hook up older equipment if need be.

Really, you have to ask?
 
Alright hand over your man card Steve.

Beepster
 
It does have what I THINK (IIRC) the standard serial port symbol above it.
 

 
Wasn't that something like; OIO ?