Device driver stream handlers communicate with the hardware PDD through the DDCMDEntryPoint. This is accomplished through the use of device driver commands (DDCMDs), which allow a stream handler to request a PDD to perform functions such as starting, stopping, or resuming a device. This interface uses the IDC mechanism provided by the ATTACHDD DevHelp function. The stream handler must attach to the device driver to receive the DDCMD entry point address of the device driver. This function is performed before issuing device driver commands.