VBB utilizes two virtualization engines. SPICE and OpenVBB.

Spice Evaluation Model

SPICE is an analog engine and computes circuits that obey Ohms law for example. SPICE virtualization engine should be used for circuits that require analog circuits. However not all components yet support SPICE.

OpenVBB Evaluation Model

OpenVBB however is a digital engine with mock-analogue behaviour models. For example OpenVBB does not calculate current(I) or other analog features. Instead common analog behaviours are modelled as mock-analog behaviours. For example the resistor pullup, pulldown and simple voltage divider behaviours are mocked using a Function property is used to select the behaviour to model. To get them most out of circuits that use resistors with OpenVBB evaluation you need markup the resistor and other mock-able models to select the correct function