According to a PR from Discreet, this patch is mainly a performance and stability update. Lots of enhancements here, the list includes:
- Overall memory efficiency.
- Performance Increases in TrackView, TrackBar, Particles, RPF, and ActiveShade.
- Workflow Enhancements in Skin, Custom Attributes, Render Elements, Subdivision Surfaces (HSDS, Meshsmooth), Parameter Wiring, Groups, ActiveShade, and PolyObjects.
- MaxScript bug fixes and enhancements.
A detailed list of all 3ds max 4.2 changes and updates is available at Discreet's website.

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