As with many facets of Windows, the icon format is steeped in history. In the early days of the 16-bit Windows operating system only the device-dependent bitmap (DDB) format was supported. Such a bitmap specified a width and height in pixels as well as a table that mapped pixels to entries in a particular device's color palette. Because different devices naturally supported different resolutions and had different color capabilities, these bitmaps were not easily moved from one device to another. DDBs were, however, very efficient and are in fact still used today for certain operations. A device-independent bitmap (DIB) format was introduced to correct all of the problems inherent in DDBs. Such a bitmap included its own color table independent of any particular device. The bitmap's pixels then mapped to the bitmap's color table, which unambiguously defined the pixel colors using red, green, and blue (RGB) color values.