Adapter device drivers receive commands through an I/O request block (IORB) entry point. The format of IORB commands received by an adapter device driver is defined in this reference.

Adapter device drivers have full use of both the 16-bit and 32-bit DevHlp services defined in OS/2 operating system. Although the adapter device driver to DM interface is 16-bit, adapter device drivers can manipulate 32-bit objects with assembly subroutines.

The service request entry point of an adapter device driver can be called in either kernel (also known as task) or interrupt contexts. Consequently, an adapter device driver must never block while servicing a request after it has completed initialization. (An adapter device driver can block at initialization.)

Service requests that involve time delays normally are initiated by the adapter device driver; then, the adapter device driver immediately returns to its caller. Service request completion is indicated to the caller using asynchronous callback notification.