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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