DOS device driver

DOS device drivers (often simply known as SYS files) are stored in a simple binary format. The filename extension  is used by the FreeDOS printer driver tool. For the block device driver of the compression software Stacker, which was also included in some versions of the DR-DOS operating system or the Novell DOS and Caldera OpenDOS offshoots, the filename extension  is used.

Drivers are loaded into a contiguous block of memory; the segment part of data structure pointers is then adjusted to match the loading segment.

Some device drivers are stored in the MZ format instead of the "raw" SYS format.

Identification
Most DOS device drivers begin with the magic ID.

Sample files

 * http://www.ibiblio.org/pub/micro/pc-stuff/freedos/files/repositories/latest/util/spool.zip → SPOOL.DEV
 * https://www.uwe-sieber.de/files/cfg_echo.zip → echo.sys
 * http://ftp.uni-bayreuth.de/pc/caldera/DR-DOS.703/images/disk02.144 → STACLOAD.BIN

Links

 * SYS file structure in Ralf Brown's