Some GARTs may have addressing limits which can't cover all of the physical addresses which may be available to the CPU.  This is an attempt to categorize chipsets. 

The maximum memory is how much you can slot in.  The memory controller address limit is how much address space the northbridge is decoding.  So, 4 GB of address space with 4 GB slotted in will result in less than 4 GB of RAM available to the OS because a chunk of address space gets reserved for the PCI and miscellaneous apertures.  The GART address limit is how much of the MC address space the GART can map to.  Status is whether we need to worry about GART addressing as a result. 
[[!table header="no" class="mointable" data="""
 manufacturer  |  chipset name  |  maximum memory  |  MC address limit  |  GART address limit  |  status 
 AMD  |  751  |  768MB  |  ??  |  ??  |  good 
 AMD  |  761  |  2GB  |  ??  |  4GB  |  good 
 AMD  |  762  |  4GB  |  4GB  |  4GB  |  good 
 AMD  |  amd64 processor  |  ??  |  ??  |  1024GB  |  good 
 Intel  |  830M/MG/MP  |  1GB  |   |  4GB  |  good 
 Intel  |  845G/GL  |  2GB  |   |  4GB  |  good 
 Intel  |  855GM/GME  |  2GB  |   |  4GB  |  good 
 Intel  |  865G/GV  |  4GB  |  4GB  |  4GB  |  good
 Intel  |  915G/GV/GL/P/PL/GL  |  4GB  |  4GB  |  4GB  |  good 
 Intel  |  915GM  |  2GB  |  4GB  |  4GB  |  good 
 Intel  |  945GM  |  4GB  |  4GB  |  4GB  |  good 
 Intel  |  G33  |  8GB  |  64GB  |  64GB  |  good 
 Intel  |  G35  |  8GB  |  64GB  |  64GB  |  good 
 Intel  |  G965  |  ??  |  64GB  |  64GB  |  good 
 SiS  |  630/730  |  1.5GB  |  ??  |  4GB  |  good 
 VIA  |  PLE133  |  1.5GB  |  ??  |  ??  |  good 
 VIA  |  [[P4M400|P4M400]]  |  2GB  |  ??  |  ??  |  ?? 
 VIA  |  KM266  |  4GB  |  ??  |  ??  |  ?? 
"""]]

Note: VIA's specs webpages don't agree with their product comparisons on maximum memory sizes around the PM800 series. 
[[!table header="no" class="mointable" data="""
 manufacturer  |  graphics chipset  |  GART address limit 
 ATI  |  Rage 128  |  4GB 
 ATI  |  R100  |  4GB 
 ATI  |  R200  |  4GB 
"""]]