Q34407: BSAVE/BLOAD File Format Explained for BASIC; 7-Byte Header

Article: Q34407
Product(s): See article
Version(s): 3.00 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | B_BasicCom B_GWBasicI | mspl13_basic
Last Modified: 9-JAN-1991

A file saved with the BSAVE statement has a 7-byte header with the
following hexadecimal format:

   ww xx xx yy yy zz zz

   ww:     A signature byte equal to 253, which tells DOS and other
           programs that this is a BASIC BSAVE/BLOAD format file.
   xx xx:  The segment address from the last BSAVE.
   yy yy:  The offset address from the last BSAVE.
   zz zz:  The number of bytes BSAVEd.

This information applies to Microsoft QuickBASIC versions 3.00, 4.00,
4.00b, and 4.50 for MS-DOS; to Microsoft BASIC Compiler versions 6.00
and 6.00b for MS-DOS; and to Microsoft BASIC Professional Development
System (PDS) versions 7.00 and 7.10 for MS-DOS.

This information is provided as is. The BSAVE format is not guaranteed
to be the same in a future release.

Microsoft GW-BASIC Interpreter (versions 3.20, 3.22, and 3.23) uses
the same 7-byte header string, and also repeats the 7-byte string,
appending it after the final data byte. BASICA (provided in IBM or
Compaq ROM on some computer models) does not repeat the 7-byte string
at the end. GW-BASIC and BASICA both terminate the file with ASCII 26,
also known as a CTRL+Z character (hex 1A). QuickBASIC and Microsoft
BASIC Compiler don't append CTRL+Z or repeat the 7-byte string at the
end.

To determine whether a file was BSAVEd by GW-BASIC, BASICA, or
QuickBASIC, compare the length of the memory saved against the file
length. The difference is 15 bytes in GW-BASIC, 7 bytes in QuickBASIC,
and 8 bytes in BASICA.

Despite the slight format differences, files BSAVEd under any of the
three above BASIC dialects correctly BLOAD into each other BASIC.

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