Prior to VisualAge Smalltalk Server for OS/390 and z/OS V6.0, the Delay timer was not implemented in the Smalltalk VM running on OS/390 and z/OS. Therefore all Smalltalk processes were forced to run at priority 3 and all wait message sends to Delay converted to a Processor>>#yield. This behavior was the same whether the LE POSIX runtime option was set ON or OFF.

Beginning with VisualAge Smalltalk Server for OS/390 and z/OS V6.0, the Delay timer is implemented when running Smalltalk with the LE POSIX runtime option set to ON in the Native batch environment (the Delay timer is not implemented when running under IMS or CICS). With POSIX set ON the ProcessorScheduler runs as described in the Programer's Reference. The priority is not forced to a priority of 3 and the wait message send is not converted to a Procesor>>#yield. With the LE POSIX runtime option set to OFF the behavior is the same as if the Delay timer is not implemented.

Prior to VisualAge Smalltalk Server for OS/390 and z/OS V6.0, all asynchronous calls were converted to synchronous blocking calls. Beginning with VisualAge Smalltalk Server for OS/390 and z/OS V6.0, in a Native Batch environment with the LE POSIX runtime option set ON and the EsAsynchronousCallout application included in the image, all asynchronous calls run on separate operating system threads. In the IMS and CICS environments the asynchronous calls will continue to be converted to synchronous blocking calls.