How the inner layers are defined is often a cause for confusion amongst new users of CADSTAR when it comes to power planes.
Why is this so?
The inner power layers are often referred to as power planes, a GND plane and a VCC plane etc.
I have only been "doing PCB's" since about 1992 so am too young for some of this but as I understand it historically the inner plane layers would be defined as a "powerplane", all is OK so far however a powerplane in CADSTAR (and most other CAD packages at the time) was displayed in the negative - that is the copper is not shown and the gaps in the copper (around the pad) are shown instead.
This stems back to ye olde days of 8086, 256k RAM and other such cobweb covered stuff that has less power than my calculator.
A positive plane was too much-too slow-too big for technology then so they were negative and the PCB manufacturers inverted them when plotting or some other unseen wizardry.
So we set the inner layer to be a powerplane in CADSTAR - whats wrong with that?
Well, if you have a single net solid plane on an inner layer you do not see where the copper is, you also do not easily see where the copper is not. Gaps in the plane are harder to visualize and pins that are not connected also harder to see.
By having the layer as a positive plane we can see exactly where the copper goes or it doesn't, we can also see the pads that do not get connected to it.
OK - so positive copper is better in the power planes - then why do we still set those layers to be negative planes you ask? This is what is often so confusing.
The reason for this is that when routing a connection can be terminated on a plane when it passes through it. That is to say that if you route a track and place a via that goes through the plane then the track will be terminated and not continue as a track on that layer. If the layer was "Electrical" then it would continue to be routed as a track.
So in order to make the task of routing the board quicker and easier we set the inner power layers to be powerplanes while we are routing, then once routing is finished we change them to be electrical and pour positive copper on them within copper pour templates.
It's simple really and now that you know this, it becomes second nature to start with powerplanes and then change them to electrical and pour copper when routing has finished.