Signatures of Macintosh Files

Summary: What are Macintosh signatures? Where are they stored? What do they mean? How can a file loose its signature? How to restore it?

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.

APPL???? Application (program)
EPSF????EPSGeneric EPS
PICT????PCTGeneric Pict
PNGf????PNGGeneric PNG
TEXT????TXTGeneric Text

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.)

CreatorFile TypExtensionComments
8BIM8BIMPSDPhotoshop 3/4 files
AB65AD65P65Pagemaker 6.5
ALB4ALD4PM4Pagemaker 4
ALB5ALD5PM5Pagemaker 5
ALB6ALD6PM6Pagemaker 6
APPLaust Self-extracting archive created by Stuffit
APPLEXTR Self-extracting archive created by Compact Pro
ART3TEXTAI Illustrator 3
ATMCsfntOTFOpen Type font file
BOBOCWWPCWKClaris Works text v. 1 to 5
BOBOWORDCWKClaris Works (word processor)
CAROPDF_PDFAcrobat files
cDRWdDRW Claris Draw
DBSEFTCHFDBImage database of Extensis' Portfolio
DDAPDDFL File compressed by Disk Doubler ??
ddskdeviDMGMacintosh disk image
dProdDOCMDPMacDraw Pro
FH50AGD1FH5Freehand 5
FHD3FHA3FH3Freehand 3
FMP3FMP3FMP/FP3FileMaker Pro
FXTCEggPAEPAfter Effects' project file
Gld1PDB_PDBPalm OS Database file
Gld1PRC_PDBPalm OS Application file
inDdinDnINDIndesign Document (also *.indd)
LWFNASPF Adobe Type 1 Font
MACAWORD Mac Write 4.6/5
MDPLDRWG MacDraw II files
MDRWDRWG MacDraw files
MFL2SPA_FLAFichiers Flash (├ęditeur)
MOSSTEXTHTMHTML for Netscape Navigator (see A Web Site on a CD for more explanations)
MSIETEXTHTMHTML for Internet Explorer (see A Web Site on a CD for more explanations)
MSWDRTF_RTFRTF produced by Microsoft Word
MSWDW6BNDOCMicrosoft Word 6
MSWDW8BNDOCMicrosoft Word 8 (98)
MSWDWDBNDOCWord 3/4/5 Macintosh
MV85MD03DIRMacromedia Director 8.5
MV93MD93DIRMacromedia Director
nX^2nX^n WriteNow 3
nX^nnX^n WriteNow 2
OMEGTEXT Mathematica (all kinds of files)
MPS_TEXTXMLXML file (in fact, ????TEXT should do the job)
PACTCPCT???Archive created by Compactor (Pro)
PnstPNRAMP3Fichier MP3 Real Player
PPT3SLD3PPTPower Point 3
PPT3SLD8PPTPower Point 98
QSfLQSfl Check file of the Symantec AV
SIT!SIT!SITArchive created by Stuffit
SIT!SITDSITArchive created by Stuffit
SSIWWP42WP4Wordperfect 4 (saved by WP for the Mac)
SSIWWP50WP5Wordperfect 5 (idem)
StMIGIFfGIFGIF files created by PageMill
StMITEXTHTMHTML files created by PageMill
SWF2SWFLSWFFlash files
ttxtTEXTTXTSimpleText File
TVODjp2_JPGJPEG 2 File by QT
TVODMooVMOVQuickTime movie files (to be used also with other video formats)
TVODMPEGMP3MP3 file for QuickTime
TVODWAVEWAVWave file for QuickTime
XPR3EPSPEPSEPS created by Xpress
XPR3XDOCQXDXpress (all versions)
ZIP_ZIP_ZIPZipped archive

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

File Types

..CTScitex files (put 8BIM as creator if you want that files open directly in Photoshop when you double-click on them on the Mac
.WAVWave sound file
.WP4PC WP4 file as seen by Wordperfect 2 for the Mac
.WP5PC WP51 file (idem)
8BIMAdobe Photoshop native format
AB65Pagemaker 6.5
ALB3PageMaker 3
ALB4PageMaker 4
ALB5PageMaker 5
ALB6PageMaker 6
AWDBMS-Works database
AWSSMS-Works spreadsheet
AWWPMS-Works word processor file
BINAText file saved as Word DOS or Word Windows file by Word Mac 5
CrTCProject file by Toast 3
CWWPClaris Works text file
DBSEImage database of Extensis' Portfolio
DCT5MS-Word dictionnary
DDFLDisk Doubler data file
dDOCMacDraw Pro file
dDRWClaris Draw File
DRWGMacDraw file
DWG_AutoCAD file
EggPAfter Effects' project file
FFILFont Suitcase (Type 1 or True Type)
ffilDisplay Font
FH50Freehand 5 file
FHD3Freehand 3 file
F#+DRag Time Classic file
FMK$FileMaker 1 file
FMP3FileMaker Pro file
GIFfGIF files created by PageMill
GLOSMS-Word glossary
HImgImage file created by Toast 3
inDdIndesign Document
jp2_JPEG 2 file
lfilTrue Type Font
LWFNType 1 Font (PostScript font)
MooVQuickTime file
MP3_MP3 file
Mp3_MP3 file
MPEGMPEG file (MPEG1 coding), also MP3
MPG3MP3 file
MPWdMacWrite Pro 1.5 file
MV93Director 5
MV85Director 8.5
MW2DMacWrite II file
MW2SMacWrite II model
nX^2Write Now 3 file
nX^dWrite Now 2 file
PACTCompactor data file
PDF_Acrobat files
PNRARealPlayer MP3 file
R#+ARagTime Classic text file
S#+ARag Time 2 text file
sfntOpen Type font file
SIT!Stuffit Archive
SITDStuffit Archive
SLD3PowerPoint 3
SLD8PowerPoint 8
SPA_Flash editor file
SWFLFlash player file
WAVEWave File
W6BNMac Word 6
W8BNMac Word 8 (98)
WDBNMac Word 3, 4, 5 text file
WHLPMS-Word help file
WORDMacWrite formatted file
WP42PC WP4 file seen by Wordperfect 1 for the Mac
WP50PC WP51 file seen by Wordperfect 1 for the Mac
WPD0Wordperfect 1 text file
WPD1Wordperfect 2 text file
WPD3Wordperfect 3 text file (what happened to the '2'?)
WPRDMS-Word print file
WTBNWord Template
XDOCXpress file
XTMPXpress template
XLBNExcel 1 spreadsheet
XLS_Excel 2.2 spreadsheet
XLS3Excel 3 spreadsheet
XLS4Excel 4 spreadsheet
ZIP_Zipped archive

Creator Strings

Please note that '_' represents a space.
8BIMAdobe Photoshop
AD65Pagemaker 6.5
AGD1Freehand 5
ALD3PageMaker 3
ALD4PageMaker 4
ALD5PageMaker 5
ALD6PageMaker 6
ART3Illustrator 3
ART5Illustrator 5 and later
ARTYIllustrator 1
ARTZIllustrator 88
ATMCAdobe Type Manager 'C' (Open Type)
BOBOClaris Works
CAROAcrobat Distiller
CDr3Toast v. 3
cDRWClaris Draw
CPCTCompactor (Pro ?)
DDAPDisk Doubler
dosaUnknown PC files
dProMacDraw Pro
ERIKFinder (Desktop files)
F#+ARag Time Classic
FHA3Freehand 3
FMK4FileMaker II ?
FMP3FileMaker Pro
FTCHExtensis' Portfolio
FXTCAfter Effects
MACAMacWrite 2.2 and 4.6
mdosDOS file copied by AFE or PC Exchange
MFL2Flash editor
MOSSNetscape (Mozilla)
MPWRMacWrite Pro
MSWDMicrosoft Word 3/4/5 for the Mac
NqstSoundEdit 16 v.2
nX^nWrite Now v. 3
PPT3PowerPoint (all versions)
PSIPWorks 1
PSI2Works 2
R#+DRag Time 3
S#+DRag Time 2
SSIWWordperfect 1
StMIAdobe PageMill
SWF2Flash player
TVODQuick Time
vgrdLaserWriter (Postscript file)
WPC2Wordperfect 2 (3 also)
XPR3QuarkXpress 3

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).

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