Apple II
File Type Notes
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                                                  Developer Technical Support

File Type:       $B5 (181)
Auxiliary Type:  All

Full Name:       ProDOS 16 or GS/OS Shell application file
Short Name:      GS/OS Shell application

Revised by:      Dave Lyons                                          May 1992
Written by:      Dave Lyons & Matt Deatherage                  September 1989

Files of this type and auxiliary type contain application programs intended
for use within a shell environment for the Apple IIgs.

CHANGES SINCE DECEMBER 1991:  Broadened the definition auxiliary type bit 1 to
mean the application can handle getting control with the Super Hi-Res screen
on.
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Files of type $B5 contain GS/OS shell application programs.  These files
contain program code in Object Module Format (OMF) that is loaded by the
System Loader or ExpressLoad at an address and is then executed under the
control of a command shell (such as APW, for example).

The shell may provide extra services to a shell application that are not
available to normal GS/OS applications (files of type $B3).  A shell
application can identify which shell it is running under by examining the
shell identifier.

Information about the shell identifier and other shell application environment
issues may be found in GS/OS Reference and APW Reference, where the shell
application environment is completely documented.  OMF is documented in those
manuals as well.  All developers creating files of type $B5 should be familiar
with this material.

The auxiliary type for $B5 files is now defined to indicate properties of the
program contained within the file.  Other parts of the system may use this
information to properly control the environment for the program:

     bits 31-16        reserved--must be 0
     bits 15-8         signature byte.  $DB means bits 7-0 are valid
     bits 7-3          reserved--must be 0
     bit 2             Message Aware:
                       1 = uses Message Center message #1
                       0 = ignores Message Center message #1
     bit 1             Desktop Application:
                       1 = application can handle the Super Hi-Res
                           screen already being on when it first gets
                           control, so the system can provide a smooth
                           visual transition into the application
                       0 = application is not prepared for the Super
                           Hi-Res screen to be on
     bit 0             GS/OS Aware:
                       1 = uses long prefixes (for example, prefix 9
                           instead of prefix 1)
                       0 = uses short prefixes (less than 63
                           characters)

   NOTE: If a Shell Application has the Desktop Application bit
         set, it should be prepared to get control with either the
         text or the Super Hi-Res screen visible.  For example, if
         some error prevents the application from using the
         desktop tools, it may be necessary to make the QuickDraw
         II call GrafOff before the user can read error messages
         displayed on the text screen (it's OK to call GrafOff
         even if QuickDraw II is not active).

         If a Shell Application does not have the Desktop
         Application bit set (or does not even have a $DBxx
         auxiliary type), the system software reserves the right
         to force the text screen to be visible if QuickDraw II is
         not started.  Do not assume that a Quit call from one
         application to another (with QuickDraw II not started)
         will leave the Super Hi-Res screen visible.