In addition to lower power requirements (no specific details were specified), the G0 stepping also contains an enhanced virtualization engine.  It comes with a newly virtualized Task Priority Register (TPR) for the Advanced Programmable Interrupt Controller (APIC).  It's a kind of internal speedup which allows tasks of higher priority to be serviced before lower priority ones.  It basically makes tasks that need immediate access a little more able to get it.  And from a software point of view, it is a desirable feature.

G0 also provides some new information relating to common string manipulation operations.  These relate to the IN and OUT operations which move data from the plug-in cards to the CPU (IN), or vice-versa (OUT).  The new stepping also sports a new CPUID code.  This uniquely identifies the type of processor and will allow software to distinguish this Clovertown from previous ones.  B3 used 06F7 while G0 now uses 06FB.  Common utilities like CPU-Z will use this information to query specific internal information about these particular Clovertowns, thereby providing its detailed summary.  The CPUID serves as a gateway into something called MSR (Model Specific Registers) which can reveal a tremendous wealth of information about a particular CPU's abilities, runtime observations, cache activity and much more.

The affected models include the entire range of Clovertowns.  The X5355, E5345, E5335, L5320 and E5310 which operate at 2.66/1.333 GHz, 2.33/1.333 GHz, 2.0/1.333 GHz, 1.86/1.066 GHz and 1.6/1.066 GHz respectively.  The familiar product codes will remain the same, but a new internal numbering scheme will be used for S-Spec and MM.  Previous Clovertowns were either 120 watt, 80 watt or 50 watt processors.  Both B3 and G0 steppings will be shipped for some time after G0's October 4 release.