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Starts a render of the current frame to "it" or Maya's Render view.   Select the option box to access preferences for rendering method, threads, etc.

 IPR Render

Starts an interactive preview rendering session.  Select the option box to access preferences for rendering method, threads, etc.

Batch Render

Starts a batch render.  Select the option box to access preferences for spooling to Tractor or LocalQueue.

Bake Render

Starts a bake render, which is a kind of batch render that bakes textures without illumination.  Select the option box to access preferences for spooling to Tractor or LocalQueue.

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