The Virtual and Real Device concept

The Osprey system concept logically "splits" the PDP-11 controller from the physical device. Much like MSCP disk controllers which can communicate with disks of different capacities, the Osprey PDP-11 controllers can talk to any number of different physical devices. There are drivers for the PDP-11 interface and separate drivers for the physical interface, as shown in Figure 10. A simple communication scheme passes data between the the two separated interfaces.

The Virtual I/O detection logic "knows" from the OSPREY.CNF file which PDP-11 peripherals are "assigned" to PC devices. Any request for I/O which cannot be found in this table is assumed to be "real", i.e. requiring a true PDP-11 I/O bus signal.

Thus, virtual I/O can be thought of as I/O assigned to the PC domain. Real I/O assumes the Osprey card set will generate actual PDP-11 backplane signals.

This Kit enables programmers to create new PDP-11 interfaces, as well as new physical interfaces. For example, a new PDP-11 interface that emulates an RM02, can be added using the Kit. Once written, the operating system (RSTS, RSX, RT, etc.) uses existing code to talk to the RM02 controller, just as it has always done. However, the Osprey has split the PDP-11 controller from the physical controller, the actual media used for the RM02 might be a host PC hard or floppy disk file, or a file on a network, or a RAM disk. Since these physical interfaces are already included with the Osprey support software, no additional programming is required, regardless of which media is desired.