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What Are Signatures?

The Macintosh doesn't use three-byte extensions (or even longer than three bytes, nowadays) to identify the very nature or contents of files, but signatures.
Signatures are strings of eight bytes, four for the creator (the program which created the file) and four for the file type (text, picture, and so on).
See also our Comments for Techies.
The correspondance between signatures and icons is managed by the Finder, for all programs which happened to exist on a volume, in the Desktop file (an hidden system file which is never shown by the Macintosh but exists on every disk). With System 7 and upwards, the Desktop graduated to a double Desktop DB + Desktop DF, for reasons which would led us too far away from our main issue.

Signatures Tables

Here are some of the signatures and corresponding PC extensions we collected (if you want to add or correct something, please feel free to send us an e-mail, we try to update the site frequently).
For those who need to edit the internal table of our Mac-PC transfer programs (MacDisk and MacImage), you will have to note the signature/extension you want to use/exploit and put it in the table displayed by the SignEdit utility (see the manual). If you encounter an atypical file (something not giving the results expected), please check the real signature of a file whose origin doesn't make any doubt, on a Macintosh magnetic volume (see the rightmost column of the display).

Generic Formats

These signatures identify the file type, but not the creator ('????' is a valid creator). They are useful when a program refuses to load a file because the signature is not what it expects and the programmer was too lazzy to look into the file. We give the PC extension when there is a well established one.

Signature Extension Comments APPL????   Application (program) EPSF???? EPS Generic EPS JPEG???? JPG Generic JPEG PICT???? PCT Generic Pict PNGf???? PNG Generic PNG TEXT???? TXT Generic Text TIFF???? TIF Generic TIFF

Specific Formats

These signatures identify both the file type and the creator. Applications other than the creator generally only look at the file type to ascertain whether they can open the file. (The '_' represents a space character.)

Creator File Typ Extension Comments 8BIM 8BIM PSD Photoshop 3/4 files 8BIM 8BPS PSD Photoshop  AB65 AD65 P65 Pagemaker 6.5 ALB4 ALD4 PM4 Pagemaker 4 ALB5 ALD5 PM5 Pagemaker 5 ALB6 ALD6 PM6 Pagemaker 6 APPL aust   Self-extracting archive created by Stuffit APPL EXTR   Self-extracting archive created by Compact Pro ART3 TEXT AI  Illustrator 3 BNHQ TEXT HQX BinHex BOBO CWWP CWK Claris Works text v. 1 to 5 BOBO WORD CWK Claris Works (word processor) CARO PDF_ PDF Acrobat files cDRW dDRW   Claris Draw DBSE FTCH FDB Image database of Extensis' Portfolio DDAP DDFL   File compressed by Disk Doubler ?? ddsk devi DMG Macintosh disk image dPro dDOC MDP MacDraw Pro FH50 AGD1 FH5 Freehand 5 FHD3 FHA3 FH3 Freehand 3 FMP3 FMP3 FMP/FP3 FileMaker Pro FXTC EggP AEP After Effects' project file Gld1 PDB_ PDB Palm OS Database file Gld1 PRC_ PDB Palm OS Application file inDd inDn IND Indesign Document (also *.indd) LWFN ASPF   Adobe Type 1 Font MACA WORD   Mac Write 4.6/5 MDPL DRWG   MacDraw II files MDRW DRWG   MacDraw files MFL2 SPA_ FLA Fichiers Flash (éditeur) MOSS TEXT HTM HTML for Netscape Navigator (see A Web Site on a CD for more explanations) MSIE TEXT HTM HTML for Internet Explorer (see A Web Site on a CD for more explanations) MSWD RTF_ RTF RTF produced by Microsoft Word MSWD W6BN DOC Microsoft Word 6 MSWD W8BN DOC Microsoft Word 8 (98) MSWD WDBN DOC Word 3/4/5 Macintosh MSWD WTBN DOT Word Template MV85 MD03 DIR Macromedia Director 8.5 MV93 MD93 DIR Macromedia Director MWII MW2D   Mac Write II nX^2 nX^n   WriteNow 3 nX^n nX^n   WriteNow 2 OMEG TEXT   Mathematica (all kinds of files) MPS_ TEXT XML XML file (in fact, ????TEXT should do the job) PACT CPCT ??? Archive created by Compactor (Pro) Pnst PNRA MP3 Fichier MP3 Real Player PPT3 SLD3 PPT Power Point 3 PPT3 SLD8 PPT Power Point 98 QSfL QSfl   Check file of the Symantec AV SIT! SIT! SIT Archive created by Stuffit SIT! SITD SIT Archive created by Stuffit SSIW WP42 WP4 Wordperfect 4 (saved by WP for the Mac) SSIW WP50 WP5 Wordperfect 5 (idem) StMI GIFf GIF GIF files created by PageMill StMI TEXT HTM HTML files created by PageMill SWF2 SWFL SWF Flash files ttxt TEXT TXT SimpleText File TVOD jp2_ JPG JPEG 2 File by QT TVOD MooV MOV QuickTime movie files (to be used also with other video formats) TVOD MPEG MP3 MP3 file for QuickTime TVOD WAVE WAV Wave file for QuickTime XCEL XLBN XLS Excel 1 XCEL XLS4 XLS Excel 4 XCEL XLS5 XLS Excel 5 XPR3 EPSP EPS EPS created by Xpress XPR3 XDOC QXD Xpress (all versions) ZIP_ ZIP_ ZIP Zipped archive

Below a more general list of filetype and creator strings we already saw (the '_' represents a space character).

File Types

Signature Comments ..CT Scitex files (put 8BIM as creator if you want that files open directly in Photoshop when you double-click on them on the Mac .WAV Wave sound file .WP4 PC WP4 file as seen by Wordperfect 2 for the Mac .WP5 PC WP51 file (idem) 8BIM Adobe Photoshop native format 8BPS Transparent AB65 Pagemaker 6.5 ALB3 PageMaker 3 ALB4 PageMaker 4 ALB5 PageMaker 5 ALB6 PageMaker 6 AWDB MS-Works database AWSS MS-Works spreadsheet AWWP MS-Works word processor file BINA Text file saved as Word DOS or Word Windows file by Word Mac 5 CCAD Claris CAD CrTC Project file by Toast 3 CWWP Claris Works text file DBSE Image database of Extensis' Portfolio DCT5 MS-Word dictionnary DDFL Disk Doubler data file dDOC MacDraw Pro file dDRW Claris Draw File DRWG MacDraw file DWG_ AutoCAD file EggP After Effects' project file EPSF EPS file FFIL Font Suitcase (Type 1 or True Type) ffil Display Font FH50 Freehand 5 file FHD3 Freehand 3 file F#+D Rag Time Classic file FMK$ FileMaker 1 file FMP3 FileMaker Pro file GIFf GIF files created by PageMill GLOS MS-Word glossary HImg Image file created by Toast 3 inDd Indesign Document jp2_ JPEG 2 file JPEG JPEG file lfil True Type Font LWFN Type 1 Font (PostScript font) MooV QuickTime file MP3_ MP3 file Mp3_ MP3 file MPEG MPEG file (MPEG1 coding), also MP3 MPG3 MP3 file MPWd MacWrite Pro 1.5 file MV93 Director 5 MV85 Director 8.5 MW2D MacWrite II file MW2S MacWrite II model nX^2 Write Now 3 file nX^d Write Now 2 file PACT Compactor data file PDF_ Acrobat files PICT PICT file PNGF PNG File PNRA RealPlayer MP3 file R#+A RagTime Classic text file RTF_ RTF File S#+A Rag Time 2 text file SIT! Stuffit Archive SITD Stuffit Archive SLD3 PowerPoint 3 SLD8 PowerPoint 8 SPA_ Flash editor file SWFL Flash player file TIFF TIFF file WAVE Wave File W6BN Mac Word 6 W8BN Mac Word 8 (98) WDBN Mac Word 3, 4, 5 text file WHLP MS-Word help file WORD MacWrite formatted file WP42 PC WP4 file seen by Wordperfect 1 for the Mac WP50 PC WP51 file seen by Wordperfect 1 for the Mac WPD0 Wordperfect 1 text file WPD1 Wordperfect 2 text file WPD3 Wordperfect 3 text file (what happened to the '2'?) WPRD MS-Word print file WTBN Word Template XDOC Xpress file XTMP Xpress template XLBN Excel 1 spreadsheet XLS_ Excel 2.2 spreadsheet XLS3 Excel 3 spreadsheet XLS4 Excel 4 spreadsheet ZIP_ Zipped archive

Creator Strings

Please note that '_' represents a space.

Signature Comments 8BIM Adobe Photoshop ACAD AutoCAD AD65 Pagemaker 6.5 AGD1 Freehand 5 ALD3 PageMaker 3 ALD4 PageMaker 4 ALD5 PageMaker 5 ALD6 PageMaker 6 APLS ?? aplt Applescript ART3 Illustrator 3 ART5 Illustrator 5 and later ARTY Illustrator 1 ARTZ Illustrator 88 BOBO Claris Works CARO Acrobat Distiller CDr3 Toast v. 3 cDRW Claris Draw CPCT Compactor (Pro ?) DDAP Disk Doubler dosa Unknown PC files dPro MacDraw Pro ERIK Finder (Desktop files) F#+A Rag Time Classic FHA3 Freehand 3 FMK4 FileMaker II ? FMP3 FileMaker Pro FTCH Extensis' Portfolio FXTC After Effects inDn InDesign MACA MacWrite 2.2 and 4.6 MDRW MacDraw MDPL MacDraw II mdos DOS file copied by AFE or PC Exchange MFL2 Flash editor MOSS Netscape (Mozilla) MPWR MacWrite Pro MSWD Microsoft Word 3/4/5 for the Mac MWII MacWrite II Nqst SoundEdit 16 v.2 nX^n Write Now v. 3 OMEG Mathematica Pnst RealPlayer PPT3 PowerPoint (all versions) PSIP Works 1 PSI2 Works 2 R#+D Rag Time 3 S#+D Rag Time 2 SCPL SoundApp SIT! Stuffit SSIW Wordperfect 1 StMI Adobe PageMill SWF2 Flash player ttxt SimpleText TVOD Quick Time vgrd LaserWriter (Postscript file) WPC2 Wordperfect 2 (3 also) XPR3 QuarkXpress 3 XCEL Excel

More Info for Techies

Signatures are often considered as strings, and the greatest part of information published on signatures is based on this assumption.
However, signatures are handled by programs as 32-bit integers, which means that when you see a filetype coded as 'TEXT', a program will see 0x54455854, or even 0x54584554, depending on whether it is big-endian or little-endian.
This is the explanation of the possible presence of spaces (very frequent) or even of cryptic characters, even of non-printable characters, in the signatures.
Please note also that Apple reserves for its own use all creator strings made only of lower case letters.
Back to Top.

Where are Signatures Stored?

These signatures, against what is often mentionned, even by knowledgeable persons, are not saved in the resource fork of each file, but in the catalog tree (on the disk, in a management structure you will [hopefully] never have to look at).
This mistake finds its origin in the fact that the programs (and only the programs, not the data files) put the icons they use in their resource fork and have to declare (in a bundle resource placed in their resource fork) the signature of the files they intend to manage, so that the Finder knows what to do when the user double-clicks on an icon. Another source of errors comes from the fact that some graphic files save in the resource fork a preview picture of the file (thumbnail to display on the desktop).

Other Resources

Two other sites may be helpful:

• Apple signature registering page
  Signatures [or at least creator strings] should be registered with Apple. This site allows you to consult the database and know whether a string is free or registered. There is no possibility to get a exhaustive list (and Apple stated publicly that there would be no such list).
• Ilan Szekely's Index
  Index to download, containing more than 30 000 signatures.