Difference between COM DLL & ActiveX control

Question

Few similarities I know..

• Both cannot execute by themself. It needs some program to instantiate it.

• COM DLL & ActiveX controls are platform independant.. (Is it so..?)

• Both requires to support the interface IUnknown & exposes three methods QueryInterface, AddRef, and Release

• It also requires be registered before using & un-registered after done with it.

But how are they different..? Can someone please list it down..!

Also my understanding is ActiveX controls are OLE custom controls (OCX).. I have heard of terms like activex dlls.. Is it one other form of ActiveX control.. or different..?

Answer 1

ActiveX is a flavor of COM. COM+, OLE, and DCOM are also flavors of COM. COM just means Component Object Model. An ActiveX object is just an OLE object that supports IUnknown.

COM is a system-level standard and provides model services to facilitate the construction of higher-level functionality. OLE and ActiveX are high-level services built on top of the COM foundation. COM, ActiveX, and OLE are very similar in nature but ActiveX and OLE provide more application-level features.