What Is an ICO File?
The Microsoft Windows operating systems allows links to be placed on the desktop as icons. Icons are contained in files following the ICO -- short for "icon" -- file format. ICO files can be identified in a directory listing because they carry the ICO file extension. Windows has used the ICO file since 1985.
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Format
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An ICO file contains a small bitmap image. A bitmap is a grid of pixels that makes up the picture. Each pixel is represented by a number that is interpreted into a color by the viewing software. The ICO format contains a preamble of codes before the bitmap image data. This header in the file gives the size of the array containing the bitmap, and the color scheme used.
Favicon
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Websites can use a special ICO file, called favicon.ico. Web browsers look for this file in the directory where a webpage is held. If it can't find it there, it looks in the root directory of the site. When it encounters the file, it displays the icon it contains next to the bookmark or favorites list entry for that site. The icon also appears in front of the address for the site. The name of the file is an industry standard. There can only be one favicon.ico per directory and this functionality will not work if the icon file has a different name.
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CUR Files
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The Windows operating system shows an icon to display the position of the on-screen cursor, which is the representation of movements made by the mouse. Computer users can alter the image representing the mouse cursor and the different pictures that can be used for this function are stored in a file with a CUR file extension. The CUR file format is exactly the same as the ICO format, except that one bit in the header indicates that it is a cursor file and not a general icon file.
Similar File Types
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Different operating systems each have their own version of the ICO file. Although their file extension is different, the contents and format of these files is very similar to the ICO file. The equivalent on the Apple Mac is the ICNS file.
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References
- Photo Credit Alexander Hassenstein/Getty Images News/Getty Images
