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OSBYTE &00 (0) - Identify Host/Operating System

On entry, X=0  - Generate error number 247 giving host and OS type
          X<>0 - Return host/OS in X

On exit,  X=host/OS type:
   0 Electron                   8 UNIX or UNIX-type system
   1 BBC                        9 6809/6309 system with "dir/file.ext"
   2 BBC B+                    17 6809/6309 system with "dir.file/ext"
   3 Master 128
   4 Master ET                 28 Commodore 64/128
   5 Master Compact            29 Texas Instruments calculator
   6 Arthur or RISC OS         30 Amstrad CPC
   7 Springboard               31 Sinclair ZX Spectrum
>=32 IBM PC-type system (DOS, Windows, etc.)


Early documentation refers to OSBYTE 0 as returning the OS version. As more systems were developed, it became more correct to refer to it returning a value indicating the host. For example, code running on a second processor will always be told what the I/O host is regardless of what the host is and what the second processor is.

Platform capabilities

Over time the OSBYTE 0 return value has evolved to become a bitmap representing the capabilities of the host system, primarily of the file system structure.

  • %000x0xxx Filenames are directory.filename/extension, eg BBC, RISC OS
  • %000x1xxx Filenames are directory/filename.extension, eg Unix, CP/M
  • %nnnxxxxx Filenames are directory\filename.extension, eg DOS, Windows

This can also be represented as:

  • %000x0xxx Directory seperator is '.'
  • %000x1xxx Directory seperator is '/'
  • %nnnxxxxx Directory seperator is '\'
  • %000x0xxx Extension seperator is '/'
  • %nnnxnxxx Extension seperator is '.'

This allow programs to use code similar to the following:


See also

Jgharston 22:41, 6 September 2007 (BST)