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File magic numbers
Magic numbers are the first bits of a file which uniquely identify the type of file. This makes programming easier because complicated file structures need not be searched in order to identify the file type.
For example, a jpeg file starts with ffd8 ffe0 0010 4a46 4946 0001 0101 0047 ......JFIF.....G
ffd8 shows that it's a JPEG file, and ffe0 identify a JFIF type structure. There is an ascii encoding of "JFIF" which comes after a length code, but that is not necessary in order to identify the file. The first 4 bytes do that uniquely.
This page gives an ongoing list of file-type magic numbers.
Jump to: Image files | Compressed files | Archive files | Executable files | Miscellaneous files
Image files
File type Typical
extension Hex digits
xx = variable Ascii digits
. = not an ascii char
Bitmap format .bmp 42 4d BM
FITS format .fits 53 49 4d 50 4c 45 SIMPLE
GIF format .gif 47 49 46 38 GIF8
Graphics Kernel System .gks 47 4b 53 4d GKSM
IRIS rgb format .rgb 01 da ..
ITC (CMU WM) format .itc f1 00 40 bb ....
JPEG File Interchange Format .jpg ff d8 ff e0 ....
NIFF (Navy TIFF) .nif 49 49 4e 31 IIN1
PM format .pm 56 49 45 57 VIEW
PNG format .png 89 50 4e 47 .PNG
Postscript format .[e]ps 25 21 %!
Sun Rasterfile .ras 59 a6 6a 95 Y.j.
Targa format .tga xx xx xx ...
TIFF format (Motorola - big endian) .tif 4d 4d 00 2a MM.*
TIFF format (Intel - little endian) .tif 49 49 2a 00 II*.
X11 Bitmap format .xbm xx xx
XCF Gimp file structure .xcf 67 69 6d 70 20 78 63 66 20 76 gimp xcf
Xfig format .fig 23 46 49 47 #FIG
XPM format .xpm 2f 2a 20 58 50 4d 20 2a 2f /* XPM */
Compressed files
File type Typical
extension Hex digits
xx = variable Ascii digits
. = not an ascii char
Bzip .bz 42 5a BZ
Compress .Z 1f 9d ..
gzip format .gz 1f 8b ..
pkzip format .zip 50 4b 03 04 PK..
Archive files
File type Typical
extension Hex digits
xx = variable Ascii digits
. = not an ascii char
TAR (pre-POSIX) .tar xx xx (a filename)
TAR (POSIX) .tar 75 73 74 61 72 ustar (offset by 257 bytes)
Excecutable files
File type Typical
extension Hex digits
xx = variable Ascii digits
. = not an ascii char
MS-DOS, OS/2 or MS Windows 4d 5a MZ
Unix elf 7f 45 4c 46 .ELF
Miscellaneous files
File type Typical
extension Hex digits
xx = variable Ascii digits
. = not an ascii char
pgp public ring 99 00 ..
pgp security ring 95 01 ..
pgp security ring 95 00 ..
pgp encrypted data a6 00 ¦.
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