An index file is a file that comprises an inventory of the recordsdata in a listing, together with details about every file, corresponding to its dimension, date, and time of creation. In Photoshop, index recordsdata are used to retailer details about the layers in a PSD file. Once you open a PSD file, Photoshop will mechanically create an index file for that file. The index file is saved in the identical folder because the PSD file and has the identical identify because the PSD file, however with a .index extension.
Index recordsdata are vital as a result of they permit Photoshop to shortly entry details about the layers in a PSD file. This info is used to show the layers within the Layers panel and to carry out operations on the layers, corresponding to shifting, resizing, and deleting them. With out an index file, Photoshop must scan your entire PSD file each time it wanted to entry details about a layer, which might be a lot slower.