This text was copied from the File Formats Encyclopaedia.

							-- mhi

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Microsoft  ships  its files compressed  with COMPRESS.EXE, for expansion
the  program  EXPAND.EXE  (how  original  ;)  )  is  used.  The  program
EXPAND.EXE  is  available  with every copy  of  MS-DOS 5.0+, the program
COMPRESS.EXE is available with several development kits, I found it with
Borland   Pascal  7.0.  The  compression  seems   to  be  some  kind  of
LZ-Compression,  as  the fully compatible?  LZCopy command under Windows
can  decompress  the  same files. This  compression  feature seems to be
available on all DOS-PCs.

OFFSET              Count TYPE   Description
0000h                   4 char   ID='SZDD'
0004h                   1 long   reserved, always 3327F088h ?

0008h                   1 byte   reserved
0009h                   1 char   Last char of filename if file was compressed
                                 into "FILENAME.EX_".
000Ah                   1 long   Original file size

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At  least  with  the  version 6.22  of  MS-DOS,  Microsoft changed their
compression  program to a new signature; The program seems no more to be
able  to restore files to their original name, if it is not given on the
command line.

OFFSET              Count TYPE   Description
0000h                   4 char   ID="KWAJ"
0004h                   1 long   reserved, always 0D127F088h ?
0008h                   1 long   reserved, always 00120003h ?
000Ch                   1 word   reserved, always 01 ?