Re: Warning on file extension ".cdf" on Windows

• To: Mark Rivers <rivers@xxxxxxxxxxxxxxxxx>
• Subject: Re: Warning on file extension ".cdf" on Windows
• From: Russ Rew <russ@xxxxxxxxxxxxxxxx>
• Date: Mon, 09 Apr 2001 16:50:39 -0600

Hi Mark,

> I just ran into a strange and troubling problem using netCDF on Windows (NT
> 4.0).  I created a large, 430MB netCDF file called "test.cdf".  As soon as I
> point Windows Explorer to the directory containing that file I observe
> "explorer.exe" consuming 100% of thw CPU and up to 900MB of RAM (on a
> workstation with 1GB of RAM).  The workstation is essentially locked up.  It
> is not possible to delete or rename the file for many minutes, even from
> another workstation, because Windows claims there has been a "sharing
> violation".
> 
> Here is what I believe is happening:  Windows thinks that files with a
> ".cdf" extension are "Channel files", which are used to display Web
> channels.  As soon as Explorer opens a directory containing a ".cdf" file it
> scans that file, even without the file itself being selected.  If the file
> is huge it consumes the entire resources of the workstation for many
> minutes.
> 
> If I create a file called "test.ncd" rather than "test.cdf" things work
> fine.  If I rename "test.ncd" to "test.cdf" the problem immediately recurs.
> 
> Moral of the story:  don't use the extension ".cdf" for netCDF files on
> Windows.
> 
> Is this a commonly known problem?  Is there a FAQ for netCDF where this is
> documented?

The recommended extension for netCDF files was originally changed from
".cdf" to ".nc", in order to avoid a clash with the NASA CDF file
extension.  Since 1994 we have recommended use of the ".nc" filename
extension in all of our documentation.  The "ncgen" tool generates
files with the ".nc" extension when invoked with the "-b" (generate
Binary) argument.

The netCDF conventions documents available from

  http://www.unidata.ucar.edu/staff/russ/netcdf/conventions.html

recommend use of the ".nc" extension when they mention file naming
conventions. 

In 1997, Microsoft submitted a specification for a "Channel Definition
Format" that used the ".cdf" for filename extensions, introducing
another potential clash and another good reason for using ".nc"
instead.  Maybe your note will help discourage the use of ".cdf" for
new netCDF files.  I'll also create an FAQ entry about the recommended
filename extension.  

Thanks for raising the issue.

--Russ

_____________________________________________________________________

Russ Rew                                         UCAR Unidata Program
russ@xxxxxxxxxxxxxxxx                     http://www.unidata.ucar.edu