Hi Andrew, yes it's the internal architecture of the program code that is significantly different for v4 (especially for the Mac version), not the UI. The UI remains almost completely the same as before.

But the native Mac build fixes numerous glitches for the Mac version that were side effects of the "Wineskin" mechanism used for v3. Stuff like Retina displays supported now, you can size windows from any edge instead of only from the corner like OSX 10.6 behavior, Full screen mode is supported, and more.

Also v4 is now a 64-bit program and so can use all system memory instead of having 32-bit limits.

There are also a lot of improvements to basic functions like file loading and display speed.

- Michael