An installable device driver lets you create a standard interface between
DOS and an otherwise unsupported hardware device.  TECH Help! covers the
following topics:

Device Driver Basics ........  general introduction to device drivers

Device Header Layout ........  data structure a the start of a driver
Device Attribute ............  bit flags that define a device

Device Requests .............  services a device driver must perform
Device Request Header .......  layout of first part of a request packet
Device Driver Errors ........  error codes a driver returns to DOS
Device Status Word ..........  device status bit flags returned to DOS
BPB: BIOS Parameter Block ...  a structure used by block devices

IOCTL Functions .............  these communicate with a driver directly

Mouse Support ...............  INT 33H fns are installed as a driver
Expanded Memory Specification  EMM Fns are installed as a device driver
DoubleSpace .................  disk-compression installed as a driver
MRCI API ....................  disk-compression installed as a driver
INT 2fH .....................  DOS extensions installed as drivers

See Also: CONFIG.SYS
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Installable Device Drivers