+This also includes access to operating system locations (e.g. hardware shadow registers) by a structure called
+"<tt/OS/".
+The names are the usual ones you can find in system reference manuals. Example:
+
+<tscreen><verb>
+...
+ OS.savmsc = ScreenMemory;
+ OS.color4 = 14; // white frame
+ if (OS.stick0 != 15 || OS.ch != 255) // key or stick input?
+...
+</verb></tscreen>
+
+Please note that memory location 762/$2FA is called "<tt/char_/" while the orignal name "<tt/char/" conflicts with the C keyword.
+
+If you like to use the OS names and locations for the original Atari 800 operating system, please "<tt/#define OSA/" before including the
+<tt/atari.h/ header file.
+If you like to target the floating point register model of revision 2 machines, put a "<tt/#define OS_REV2/" before including <tt/atari.h/.
+
+Access to the Basic programming language zero page variables is established by the structure "<tt/BASIC/".