I am a holder of imac computer. How do I speed up the display of 'preview of raw files? How should I set the parameters?
You definitely want to turn off RAW rendering and use the embedded JPEG previews. Much faster and the preview produced by the camera is in most cases more than satisfactory.
In the Caching preferences you can set the Memory Cache to 512 MB, but I don't suggest making it any higher.
-Kirk
