Can I use a DLL created in Labview 5.1 in a VI created in Labview 8.6 and vice versa?

[varma]

I have some DLLs that were created in Labview 5.1. Now I may require to use them in a VI that I am creating in Labview 8.6. I would like to know if this is possible? And I am also curious to know if I can use the DLLs created in Labview 8.6 in Labview 5.1 VI.

[nathand]

I thought I'd seen this question asked somewhere before, but I can't find the thread. In theory there should be no problem. However, you'll need to have both the LabVIEW 5.1 and LabVIEW 8.6 run-time engines installed, and I don't know if there are any operating systems on which both of those versions are supported. If the run-time engine is properly installed, then calling a LabVIEW-built DLL is just like calling any other DLL. There might be some special optimization if the calling application and DLL both use the same version of the run-time engine.