VIA Apollo Pro 133/133A Motherboard Roundup - February 2000

The flexibility of the Apollo Pro 133/133A chipsets is seen in the number of different expansion slot configurations motherboard manufacturers will use with the chipsets.  The reason for this flexibility is because that, with the 686A Super South Bridge and its integrated ISA bridge, the costs associated with adding ISA slots to a motherboard layout are reduced to the costs of the physical slots themselves.  This is in contrast to the i820 chipset, for example, where an extra PCI-to-ISA bridge must be placed on the motherboard which occupies expensive space on the PCB. 

We have seen 133A boards with 1, 2 and even 3 ISA slots as well as boards with a full 6 PCI slots.  Keep in mind that if you have a motherboard outfitted with 6 PCI slots, one of those six will act as a slave slot unless the motherboard manufacturer has made provisions to support 6 master slots.  As of the time of publication, only Microstar had been shipping motherboards with this PCI arbiter chip, but since there is a relative lack of demand for 6 PCI master slots, it is unlikely that you’ll see more manufacturers adopt such a provision. 

The beauty of the flexibility of the 133A chipset is that users with legacy ISA cards can find a motherboard with enough ISA slots to accommodate their needs but at the same time those users that have made the shift to PCI peripherals should have no problem finding a motherboard with at least 5 PCI slots. 

The downside to all of this is that without more motherboard manufacturers adopting PCI-only layouts, it will take even longer to get rid of legacy ISA slots and ISA peripherals. 

Another interesting situation with 133A based boards is that not all of them feature AMR slots.  This is the exact opposite from the i820 motherboard situation where every board features an AMR slot. 

The explanation behind this is two fold:

1)      Some motherboard manufacturers are still using the 596B Mobile South Bridge, which does not feature an AC’97/MC’97 controller, which prevents them from outfitting boards based on the 596B with an AMR slot

2)      The AMR slot was never intended to be a retail option, only an option for OEMs.  The idea of purchasing AMR upgrades, etc… after market is something that was never intended as a possible use for AMR.  VIA isn’t as strict as Intel in terms of enforcing technological implementations on motherboard designs, and thus when a motherboard manufacturer refuses to make use of an AMR slot, VIA doesn’t see a huge problem with that. 

A combination of those two factors is keeping AMR slots off of quite a few of VIA based motherboards.  Motherboard manufacturers will outfit their boards with AMR slots if their OEMs demand the option, but unless they have a specific need to they will not