mapping a drive?

Error 85 simply means that the drive was already mapped, and the script could not re-map it.

what does this mean? why does a computer map a drive, or what does mapping a drive do?

 

Mapping is a pretty accurate description of what's being done when you tell your local machine's OS where to find a network resource like a folder on a drive on another computer. You're simply assigning a drive letter (like M: ) to a location like \\otherpc\shareddrive\sharedfolder\ rather than having to navigate to that location manually every time you want to access it.

 

Mapped drives also tend to have better performance than URIs do, simply because Windows keeps more information readily available so handshaking isn't being done all the time. Also, some applications (especially legacy ones) simply do not work if you try to point them to a network share, but will work fine with a mapped drive.

The command to map a drive looks like this:
net use x: \\server\share

If drive x: already exists, the command exits with an error. By default Windows will try to reconnect to any mapped drives it had when a user was last logged on, so a logon script which tries to emap the drive will throw an error 85. It's important to run that command every time, however, because if Windows can't connect to the share at logon for some reason it throws the connection away permanently.

If you wish to eliminate the error, you can change the command in the logon script to:
if not exist x: net use x: \\server\share

But it isn't necessary.