User`s guide

.GZ GZip PC archive format often used for storing A2 emulator
disk images (GS GZPK v2 plus PMPUnZIP or Angel; PC WinZIP)
.HDV Raw (DSK) ProDOS ordered disk image file 800K or greater in
size; used by emus as a virtual hard disk (ASIMOV2 on IIgs)
.HQX Mac BinHex file. [TEXT] (BinHex on Mac or GScii)
.HTM HTML [TEXT] with embedded Text commands (Web
browsers, web editors, etc.)
.IMAGE Diskcopy images (see .DIMG)
.IMG Type IMG or "user #7" Copy II Plus disk image file (A2
Copy II Plus v6.x or v7.x)
.IMG is sometimes used for Diskcopy images (see .DIMG)
.JPG PC JPEG hi-res, hi-color graphics format (GS JPEG.VIEWER,
etc. B/W only or PC, Unix viewers)
.LBR a multi-file, non-compressed A2 archive (Librarian)
.LHA LHA Archive (PC/Amiga LZH program)
.LZH LZH Archive (PC/Amiga LZH program)
.NIB emulator disk image (typical length: 232960) for protected
5.25" software (A2 Saltine's Super Transcopy)
.PCX PC graphics format (GS Convert 3200; PC many viewers)
.PD compressed GS multi-palette graphics file w/o
palettes (GS SuperPac)
.PNG PC PING hi-res, hi-color graphics format (PC viewer)
.PO a .DSK file specified as having data in "ProDOS Order"
i.e. uses ProDOS sector ordering (A2 DSK2FILE and GS ASIMOV)
.PS compressed GS multi-palette graphics file with
palettes (GS SuperPac)
.QQ BLU archive. (ShrinkIt*)
.SDK ShrinkIt disk image, usually NuFX-compressed (ShrinkIt*)
.SEA Self-extracting A2 ShrinkIt* or Mac ShrinkIt archive
(depending upon kind, run on Apple IIgs or Mac)
.SHK usually an A2 NuFX-compressed archive; non-A2-compatible
Mac .SHK archives also exist (GS ShrinkIt* / Mac unshrinker
utility / PC Nulib-- does not extract GS resource forks)
.SIT Mac StuffIt archive. (Stuffit on Mac or GS ShrinkIt)
GS-ShrinkIt will not decode StuffIt Deluxe files.
.TAR Unix Tape Archive (Unix tar with -xvf option, GS EXE tar)
.TGZ Gzipped .TAR file
.uu Unix uuencode file [TEXT] (//e uudecode, Unix uudecode)
.uue Unix uuencode file [TEXT] (//e uudecode, Unix uudecode)
.TIFF Graphics format (GS SHR Convert)
.TXT [TEXT] An ASCII text file (Text editors,
word processors, etc.)
.UU Unix uuencode file [TEXT] (A2 uudecode or Unix uudecode)
.UUE Unix uuencode file [TEXT] (A2 uudecode or Unix uudecode)
.Z Compressed file (GS-ShrinkIt or Unix uncompress)
.ZIP PC Zip Archive (GS PMPUnZIP or UNZIP [GS Shell EXE]
or PC WinZIP, PKUNZIP, Unix unzip)
.ZOO PC Zoo Archive (GS-ShrinkIt??? or PC ZOO program)
* Note: GS-ShrinkIt (= GSHK) can handle all ShrinkIt files except
.SDK (shrunken disk) files of 5.25" DOS 3.3 disks created by
8-bit ShrinkIt. 8-bit ShrinkIt does not work for GS
files having a resource fork or GS .SEA files.
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From: Apple's ftp site ...