Q: What are the major differences between Release 2,3,4 of 3D Studio.

A: If you take R2 as a base, here are some major changes in R3 and R4:

*R3 System:
-Vibrant In-Line Drivers support
-Extended IPAS capabilities
-New KXP and BXP IPAS types

*2D Shaper:
-2D Booleans

*3D Editor
-64 custom wireframe colors + select by color
-Improved Booleans
-Spotlight Overshoot for quasi shadowcasting omnilights
-Light Attenuate ranges
-Light Exclude function
-Projector Spotlight
-Rectangular Spotlight
-Box texture mapping
-PXP loader

*Keyframer
-Morph Materials & Smoothing
-Hide Object Key
-KXP loader

*Material Editor
-New Metal Shading mode
-Exclusive wireframe mode control
-Face mapping
-2 Texture map slots
-New mapping slots for opacity,self illum. etc bitmap control
-Mask control for every texture map slot
-Map adjustment controls (UV size/position/rotation) for every map type
-New combined Decal+Tile mode
-Bitmap Tinting,Inverting etc.
-New transparency mode (Sub/Add)
-Make Current command

*Renderer
-High-quality Anti-Aliasing
-64bit internal rendering
-Improved speed
-Render Region/Blowup/Object for fast previews
-Object/Scene Motion blur
-Raytracing Shadows
-Legal color checking
-JPEG support
-Layered Fog

Release 4:
*System:
-Improved Vibrant drivers for real-time shading.
-Improved IPAS - Z-buffer access.
-Image browser built-in

*3D Editor
-Realtime Camera Perspective Match/Preview

*Keyframer:
-Inverse Kinematics
-Keyframe Scripting Language
-Realtime Camera Preview

R4 added most of the new features using IPAS modules, so it is sometimes called R 3 1/2. If you create only still images, nobody can tell if it was R3 or R4. For animations however the clear choice is R4.

I am sure I have missed many things, I remember there was a list of over 200 improvements as R3 came out.

Addition:

IPAS modules written for R2 will work with Release 3 and 4. IPAS modules written for R3 will work with R4, but NOT with R2. Some IPAS modules require R4 ONLY! Check the IPAS index of Rendert**ls for more info on this.