The bitmap (.BMP) files that the Image Editor produces are device-independent monochrome or color bitmaps. Each .BMP file defines one bitmap. Bitmaps that you create and save using the Image Editor can range in size from 1-by-1 to 72-by-72 pixels.
Unlike bitmap files, icon (.ICO) and cursor (.CUR) files define a family of images. Each image in an icon or cursor file is designed for display on a different kind of device. The Image Editor distinguishes the different kinds of images by pixel dimensions and color capabilities. For example, when the application wants to use an icon, it requests the icon by name. Windows then selects the appropriate icon image in the specified file according to the pixel dimensions and color capabilities required by the device driver.