Thumbs.db is a system file generated automatically by Windows XP and earlier version of Windows in case you are viewing the contents of a particular folder in Thumbnail or Filmstrip view. It is a thumbnail cache used by Windows Explorer to speed up the display of images as the smaller images do not need to be recalculated every time the user views the folder. The cache is created when the user opens the folder for the first time and is stored locally as a hidden file.
Windows stores thumbnails of graphics files, and certain document and movie files, in the thumbnail Cache file, including the following formats : JPEG, BMP, GIF, PNG, TIFF, AVI, PDF,PPT and HTML.
The file is created locally among the images, however, preventing system wide use of the data and creating additional data load on removable devices. Each thumbnail created in a directory is represented in this database file as a small JPEG file, regardless of the file’s original format. The images are resized to a maximum of 96×96 pixels, or a proportional miniature of their original shape for non-square images, with 96 pixels on the longer side.
Each folder with Thumbnails or Filmstrip view, will have a Thumbs.db file. Folders with pictures also display previews on their icon when displayed in Thumbnail mode – the first four images in the folder at 40×40 pixels (or proportionally shaped), with a 1-pixel divider overlaid on a standard large folder icon. The Thumbs.db file is stored in OLE Compound Document format.
Thumbs.db in Windows Vista and Windows 7
Thumbs.db files are created in Windows Vista and Windows 7 as well but they are not stored locally (in the same folder). Instead they are now created and stored centrally (at a common place) on the system. This provides the system with access to images independent of their location, and addresses issues with the locality of Thumbs.db files.
The cache is stored at %homedrive%\Users\%username%\AppData\Local\Microsoft\Windows\Explorer as a number of files with the label thumbcache_xxx.db (numbered by size); as well as an index used to find thumbnails in each sized database. However, when browsing network shares with write permission, Windows Vista SP1 stores a Thumbs.db file in the remote directory instead of using the (local) central thumbcache