/G{3|4|5|6|B}
These options tell the compiler to optimize code generation for the specified processor.
/G5 optimizes code for the Intel Pentium processor. It sets the value of the _M_IX86 preprocessor macro to 500.
/G6 optimizes code for the Intel Pentium Pro, Pentium II, and Pentium III processors. It sets the value of the _M_IX86 preprocessor macro to 600.
/GB, which is the default option, blends optimizes optimizations for the 80386, 80486, and Pentium processors. It sets the value of _M_IX86 to 600, indicating that the Pentium is the dominant processor in the blending.
/G3 and /G4 optimized for 80386 and 80486 processors. The compiler accepts these options for compatibility reasons, but they have no effect.
Compiler Options | Setting Compiler Options