In computer programming, a Visual Basic Extension (commonly abbreviated VBX) or custom control, was the component model used in Microsoft Visual Basic versions 1.0 to 3.0. It is still supported in the 16-bit version of version 4.0, but was obsoleted by OCXs. VBX has also been supported in some versions of Borland Delphi. Visual Basic 4.0 added support for the newer OLE Controls or OCXs (which became ActiveX controls), implicitly deprecating VBX controls. OCXs are based on the Component Object Model.