MapPath throws an exception when "COM1"-"COM9" occur in the path - asp.net

Question

I'm using .net 4 (and 4.5) and have noted some unusual exceptions when calling Server.MapPath("COM1") or variants thereof, where the digit can be 1-9
Here's some output from my Immediate Window
Server.MapPath("hi")
"d:\\dev\\test\\WebApplication2\\WebApplication2\\hi"
Server.MapPath("COM")
"d:\\dev\\test\\WebApplication2\\WebApplication2\\COM"
Server.MapPath("COM1")
'Server.MapPath("COM1")' threw an exception of type 'System.Web.HttpException'
base: {"Failed to map the path '/COM1'."}
WebEventCode: 0
Server.MapPath("COM2")
'Server.MapPath("COM2")' threw an exception of type 'System.Web.HttpException'
base: {"Failed to map the path '/COM2'."}
WebEventCode: 0
...
Server.MapPath("COM9")
'Server.MapPath("COM9")' threw an exception of type 'System.Web.HttpException'
base: {"Failed to map the path '/COM9'."}
WebEventCode: 0
Server.MapPath("COM10")
"d:\\dev\\test\\WebApplication2\\WebApplication2\\COM10"
Server.MapPath("COM0")
"d:\\dev\\test\\WebApplication2\\WebApplication2\\COM0"
Server.MapPath("/blah/COM1.jpg")
'Server.MapPath("/blah/COM1.jpg")' threw an exception of type 'System.Web.HttpException'
base: {"Failed to map the path '/blah/COM1.jpg'."}
WebEventCode: 0
Server.MapPath("/blah/COM1NOT.jpg")
"d:\\dev\\test\\WebApplication2\\WebApplication2\\blah\\COM1NOT.jpg"
Server.MapPath("/blah/_COM1_.jpg")
"d:\\dev\\test\\WebApplication2\\WebApplication2\\blah\\_COM1_.jpg"
What is going on?

Answer 1

These are reserved words.
Do not use the following reserved device names for the name of a file:
CON, PRN, AUX, NUL, COM1, COM2, COM3, COM4, COM5, COM6, COM7, COM8,
COM9, LPT1, LPT2, LPT3, LPT4, LPT5, LPT6, LPT7, LPT8, and LPT9. Also
avoid these names followed immediately by an extension; for example,
NUL.txt is not recommended. For more information, see Namespaces.
https://superuser.com/questions/467782/why-cant-i-create-a-folder-named-com1
Thanks to: shree.pat18