The disk directives has the following format:
.disk OPT_WRITERNAME [...DISK PARAMETERS..] { [..FILE1 PARAMETERS..], [..FILE2 PARAMETERS..], [..FILE3 PARAMETERS..], .... }
The writer name is optional, if left empty the default disk writer is called. Otherwise the writer name is used to look up a 3rd party disk writer imported from a plug in. In the following sections described how the default writer works.