## Physical Device Driver Reference

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### Compatibility with Previous-Level DOS Device Drivers

Not all previous-level (any level prior to DOS 5.0) DOS device drivers can be allowed to run in a DOS session. The supported set of previous-level device drivers has the following restrictions:

Previous-level block device drivers are not permitted in a DOS session. Block device drivers must be written to the OS/2 interfaces.

Only a limited set of previous-level character device drivers can be supported by OS/2. In order to run in a DOS session, a previous-level character device driver must conform to the following rules:

-The character device driver cannot have a hardware interrupt handler. The device must be a polled device rather than an interrupt-driven one.

-The character device driver can be called by the OS/2 operating system in a DOS session, with all of the packets supported by character devices:

0 - INIT
3 - IOCtl input
4 - INPUT (read)
5 - NON-DESTRUCTIVE INPUT NO WAIT
6 - INPUT STATUS
7 - INPUT FLUSH
8 - OUTPUT
9 - OUTPUT with verify
10 - OUTPUT STATUS
11 - OUTPUT FLUSH
12 - IOCtl output
13 - DEVICE OPEN
14 - DEVICE CLOSE
16 - GENERIC IOCtl
31 - INIT Complete