As you might expect, it is perfectly possible for a request from a DP4 program running on a Windows based Client to be handled by a Unix or Linux server (even one running on a different type of processor). In fact any DP4 network manager can handle requests from any DP4 network client as long as they are from compatible releases of DP4, and the network protocols are compatible.
In release 4.520/4.616 DP4 networking was substantially reworked and for TCP/IP only is not compatible with earlier releases. It is not possible to access a 4.520 tcpmgr from a pre 4.520 TCPx, or vice versa. Attempting to do so will cause a DP4 system error, but should not cause problems other than to the affected client.
There are special considerations when setting up an environment where Windows clients running DP4 4.6xx access a server running 4.5xx DP4 on Linux or Unix. If you are using the client-only configuration, then your Windows programs will access the system database on the Unix server. The 4.5xx system database is not compatible with 4.6xx. Therefore when setting up the server you must install the 4.6xx System database from the Windows installation onto the Unix server. 4.5xx programs Unix can use the 4.6xx system database with no problems, though the display may look a little odd in a few programs.
You cannot pass requests from a requester running one protocol into a network manager running on another protocol, (and for NetBIOS the underlying transport must also be the same as is explained in the NetBIOS Networking notes). However, it is possible, though rather unusual, for a network manager to pass its requests into a second network requester running another protocol.
If you want to do this, then load the machine as you would a normal server, replacing the command that loads the database manager with one that loads a network requester instead. See Using the Network Manager as a Bridge for further details.
In principle you can also run two network managers for different protocols on the same server, one handling requests for one protocol, and one for another. However, this is unsafe if multiple resilience clients are used - in this case you should use a Bridge Configuration. For ordinary servers, if you want to load servers for more than one protocol simply duplicate the lines that load the network manager for one protocol, changing the name of the network manager, and any network specific command tails as required.