Sandman
To the pixels. nospam is incorrect here. All LR adjustments are applied to a preview file and saved to disk.

nospam
the changes are rendered on the fly and may be cached to disk (which is the preview file you're talking about). the latter is optional.

Sandman
It's not optional. All images in LR are always rendered as previews. They are kept inside your LR library.

nospam
it is not a pixel editor.

Sandman
Sure it is, only in another sense than old Photoshop. Every single adjustment you make in LR are applied to the pixels and saved to disk as a preview image. Difference is that the original file is always kept intact so every step is fully reversible.

In fact - using smart filters in Photoshop is *less* of a pixel editor than LR these days, because the pixels are never touched, it's all kept in RAM and the resulting image is never saved to disk until you export/save it. Also, fully reversible of course. :)