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File Format Specification Index



Basic Description

These files are used by Windows 3.x and Windows95 to display the mouse cursor. Win95 also uses ANI files for colored, animated mouse cursors. There may be more than one image in this file.

Basic File Format

Name Size Description
Reserved 2 byte =0
Type 2 byte =2
Count 2 byte Number of Cursors in this file
Entries Count * 24 List of cursors
   Width 1 byte Cursor Width (most commonly =32)
   Height 1 byte Cursor Height (most commonly =32)
   ColorCount 1 byte =0 !
   Reserved 1 byte =0
   XHotspot 2 byte Hotspot's X-Position
   YHotspot 2 byte Hotspot's Y-Position
   SizeInBytes 4 byte Size of (InfoHeader + ANDBitmap + XORBitmap)
   FileOffset 4 byte FilePos, where InfoHeader starts
  repeated Count times
InfoHeader 40 byte Variant of BMP InfoHeader
  Size 4 bytes Size of InfoHeader structure = 40
  Width 4 bytes Cursor Width
  Height 4 bytes Cursor Height (added height of XORbitmap and ANDbitmap)
  Planes 2 bytes number of planes = 1
  BitCount 2 bytes bits per pixel = 1
  Compression 4 bytes Type of Compression = 0
  ImageSize 4 bytes Size of Image in Bytes = 0 (uncompressed)
  XpixelsPerM 4 bytes unused = 0
  YpixelsPerM 4 bytes unused = 0
  ColorsUsed 4 bytes unused = 0
  ColorsImportant 4 bytes unused = 0
Colors 8 bytes since BitsPerPixel = 1 this will always be 2 entries
  Color 0 Red 1 byte Background color red component =0
  Color 0 Green 1 byte Background color green component =0
  Color 0 Blue 1 byte Background color blue component =0
  reserved 1 byte =0
  Color 1 Red 1 byte Foreground color red component =255
  Color 1 Green 1 byte Foreground color green component =255
  Color 1 Blue 1 byte Foreground color blue component =255
  reserved 1 byte =0
XORbitmap see below monochrome bitmap
ANDbitmap see below monochrome bitmap

Raster Data encoding

Pixels are stored bottom-up, left-to-right in the same manner as monochrome BMPs. Pixel lines are padded with zeros to end on a 32bit (4byte) boundary. Every line will have the same number of bytes. Every byte holds 8 pixels, its highest order bit representing the leftmost pixel of those. Remember padding with zeros up to a 32bit boundary (This can be up to 31 zeros/pixels!). Although there are 2 color table entries, I haven't seen a file that uses them, since Windows seems to ignore its contents.
Whenever Windows draws a cursor the ANDbitmap is applied to whatever is on the screen. After that, the XOR Bitmap is applied. Both bitmaps are encoded in the same scheme as monochrome BMPs. When there is more than one cursor in the file Windows uses the one that matches the system settings.
AND XOR Result
0 0 Black pixel
0 1 White pixel
1 0 Transparent Background pixel
1 1 Inverted Background pixel


Since CUR Files are a derivatives of BMPs they should be quite easily converted into monochrome BMPs with twice the cursor's height. Due to the XOR-AND-scheme which may not apply to other OS, these files are not very portable, and were never intended to be. 2byte and 4byte entries are stored in Intel order (Least significant byte first)

Trademarks, Patents and Royalties

To my knowledge: none
(please read the disclaimer)

Cross-Checking Software

This section is for programmers, who wish to cross-check their implementation with others. This is an incomplete list of programs, which are available as freeware / shareware / try-before-buy etc.
The following software is able to decode CURs::

MS-Windows itself (obviously not freeware)

most resource construction sets (included in Windows Compilers)
The following software is able to encode BMPs
most resource construction sets (included in Windows Compilers)

Online Resources


Paper Resources

Windows SDK


This is not the official format documentation. Although we're doing our best to keep this information as accurate as possible, there is no way of checking all of it under all possible circumstances. We're not taking any responsibility for the results of these information or lack thereof. The 'trademarks, patents and royalties' section is here just for your convenience, and is in no way complete. Please send us a note, if you find any incorrect of missing information.