Windows 1.0 Icon

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File Format
Name Windows 1.0 Icon
Extension(s) .ico

The Windows 1.x variant of the ICO format is used in Microsoft Windows versions 1 and 2 to define monochrome icons. It has little in common with the ICO format used by Windows 3 and above.


Files begin with a little-endian word, which is one of:

Value Meaning
0001 Device-Independent Format
0101 Device-Dependent Format
0201 Both formats

This is followed by a 12-byte header describing the icon bitmap:

Offset Type Meaning
0000 DWORD Not used (corresponds to hot spot X/Y in the Windows_1.0_Cursor format).
0004 WORD Width of bitmap in pixels
0006 WORD Height of bitmap in pixels
0008 WORD Width of bitmap in bytes
000A WORD Not used (corresponds to cursor color in the Windows_1.0_Cursor format).

Two bitmaps come after the header, each csHeight * csWidthBytes bytes long. The first bitmap is ANDed with the screen pattern; then the second is XORed on top of it.

A file in 'device independent' format is stored at double its eventual size (so a 32×32 icon would be saved as a 64×64 bitmap). A file in 'Both formats' format contains the header and bitmaps for the 'device-independent' version of the bitmap, followed by the header and bitmaps for the 'device-dependent' version.

See also

Sample files

  • Samples can be found in the Windows 2.x DDK, or generated with the Windows 1.x / 2.x icon editor ICONEDIT.
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