Excellon drill format
Excellon drill format is a file format used by drilling and routing machines from Excellon. It is a subset of RS274D, and is considered an industry standard. The Gerber format has similar uses, and there are utilities to convert between the formats.
Excellon drill format consists of a series of commands in a text file, one per line, with a header (starting with command M48 and ending with command M95; the header is optional) and a body.
There are two different formats (FMAT 1 and FMAT 2) which have different commands in the body section.