## Pen for OS/2 Device Driver Reference

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### Support Level Control

The level of Pen for OS/2 system extension support is passed to the pen device driver with the START_LOGICAL_DEVICE IDC request. The support level can be used to distinguish old versions of the Pen for OS/2 system extension with fewer capabilities and different structure layout from the expected level. The pen device driver can choose to support back levels by disabling functions and supplying the expected control block layouts, or the pen device driver can decline to register its devices.

Likewise, the pen device driver identifies its level to Pen for OS/2 in the driver-specific capabilities packet (driver unit 0 capabilities packet), so Pen for OS/2 can interpret the pen device driver's communication or can choose not to identify its Pen for OS/2 Device Driver Services.

The driver-specific capabilities packet identifies the level of the IOCtl interface, Pen for OS/2 Device Driver Service IDC interface, Pen for OS/2 extended information packet interface, and version of the pen device driver .