CUPS reads the file /etc/cups/mime.convs (and all other files named with a *.convs suffix in the same directory) upon startup. These files contain lines naming an input MIME type, an output MIME type, a format conversion filter that can produce the output from the input type, and virtual costs associated with this conversion. One example line reads like this:

application/pdf         application/postscript   33   pdftops

This means that the pdftops filter will take application/pdf as input and produce application/postscript as output; the virtual cost of this operation is 33 CUPS-$. The next filter is more expensive, costing 66 CUPS-$:

application/vnd.hp-HPGL application/postscript   66   hpgltops

This is the hpgltops , which processes HP-GL plotter files to PostScript.

application/octet-stream

Here are two more examples:

application/x-shell     application/postscript   33    texttops
text/plain              application/postscript   33    texttops

The last two examples name the texttops filter to work on text/plain as well as on application/x-shell . (Hint: This differentiation is needed for the syntax highlighting feature of texttops ).