Lightroom and Photoshop use the same ACR, Adobe Camera Raw module, to process the photos in the
Develop module. The difference between Lightroom and Photoshop is that the ACR is built-in Lightroom, while in Photoshop it’s a stand alone application.
Develop module reads a photo for the first time, Lightroom renders the photo as a full 1:1 preview and adds that photo to the Camera Raw Cache. So the next time it will not have to render that photo again, instead it will read the photo from the disk. The problem is that there is only so much cache. By default, the
Camera Raw Cache size is only 1 Gigabyte. It’s not that many photos, so the older photos are removed from the
Camera Raw Cache to make space for the newer photos.
When you load the photo in the
Develop module, Lightroom will look first look for that photo in the
Camera Raw Cache. If it’s not there, the
Develop module will render the photo, save the photo in the
Camera Raw Cache and then display the display the photo.
You can change the size of the
Raw Cache to whatever you can or have space for, you can also change the location of it:
File Handling >
Camera Raw Cache Settings
Lightroom: Camera Raw Cache Settings
My current default is 10 Gigabytes.