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

The Chipset

The VIA Apollo Pro 133/133A chipset is a unique entity primarily because of its flexibility as a chipset.  Motherboard manufacturers can easily adopt their BX designs for use with the 133, and with a bit more work they can modify it for the 133A. 

The North Bridge of the Apollo Pro 133 chipset is the VT82C693A, the ‘A’ at the end of the string denoting that it supports the 133MHz FSB frequency which its predecessor, the VT82C693 did not support. 

With its 133MHz FSB support, there is also support for the 1:2 AGP clock ratio, meaning that the AGP bus can be set to operate at 1/2 the FSB frequency.  This is in addition to the 1:1 and 2:3 ratios that were brought over from the old Apollo Pro Plus and are also supported by the Intel BX chipset.  Other than the i820 and i810E chipsets, the Apollo Pro 133 is the only other chipset to support the 1:2 AGP clock ratio. 

The 693A supports AGP 2X as well as up to 2GB of SDRAM or Virtual Channel SDRAM which can operate at the FSB frequency – 33MHz, FSB + 33MHz or at a frequency equal to that of the FSB. 

The VIA Apollo Pro 133A makes use of the VT82C694X North Bridge, otherwise known as the 694X.  The 694X differs from the 133’s 693A North Bridge in that it supports AGP 4X, which increases the pin count of the chip.  This unfortunately means that the 694X cannot be dropped into a 693A motherboard design without any modifications to the layout itself. 

Other than the AGP 4X support, the 694X’s feature set is identical to the 693A since they are essentially the same chip.

The South Bridge that can used with the 693A and the 694X isn’t North Bridge dependent, meaning that a motherboard manufacturer could choose to use the 693A North Bridge with the same South Bridge as a 694X based board.

The two options motherboard manufacturers have when choosing a South Bridge are the 596B or the 686A.  The 596B is known as the Mobile South Bridge and VIA uses the term Super South Bridge to define the 686A.  Taken from our VIA Apollo Pro KX133 Review (the KX133 has the same South Bridge options), here are some of the benefits the 686A offers over the 596B and other South Bridge solutions:

·        Inter-operable with VIA and other Host-to-PCI Bridges – As we just finished discussing, the fact of the matter is that the 686A can be used on a number of VIA chipset implementations, thus helping to keep costs down since VIA only has to manufacture one chip that can be implemented on a number of motherboard designs.

·        Integrated PCI-to-ISA Bridge – This feature, present on the now old Intel piix4 and piix4e South Bridges but absent on the i820 and i810(E) chipsets, allows for the implementation of ISA slots on a motherboard that uses the 686A without having to use an external PCI-to-ISA Bridge.  This helps save PCB space and cut costs.  On the reverse side of things, ISA slots are quickly dying, so this feature is becoming less of a necessity.

·        Ultra ATA 33/66 PCI EIDE Controller – Ultra ATA 33 has just recently began to be saturated by the latest 7200 RPM IDE hard drives, so Ultra ATA 66 support is definitely a desired feature.  While Intel is supposed to announce ATA-100 support in the near future, it will be a while before hard drives saturate the 66MB/s peak transfer rates of the Ultra ATA 66 specification.

·        Integrated Super I/O Controller – Unique to the 686A, the integrated Super I/O controller takes care of all of the basic I/O needs of a motherboard.  It provides the serial, IR, and parallel ports as well as the Floppy Disk Controller for the motherboard.  Why is this so special?  Well, currently no Intel chipset has these features integrated into any part of the chipset, meaning they have to resort to an external I/O controller to provide these functions.  This external controller not only occupies PCB area on the motherboard it also adds the cost of another chip to the price of the motherboard.  This is a feature the AMD 756 South Bridge does not support, one reason why many motherboard manufacturers chose to go with the 686A over the AMD 756 in their Athlon motherboard implementations.

·        AC’97 & MC’97 Support – VIA based motherboards that take advantage of the Audio Codec ’97 support of the 686A South Bridge will feature an AC’97 controller placed on the motherboard that drives an integrated audio output while supporting the use of the AMR (Audio Modem Riser) slot for higher quality audio or modem support.  The reason for the use of the AMR slot is to place the more sensitive components on an AMR slot so that motherboard manufacturers don’t have to increase the production time of their products because of the certification required for sensitive analog components such as those on modems or higher quality audio devices.  This is also why, in spite of the presence of the AMR slot, the motherboard manufacturers will go ahead and include audio inputs/outputs on the motherboard itself, so they don’t have to worry about the certification time required by an AMR card in order to ship their boards to OEMs with integrated sound.

Remember that these AC’97 controllers depend on the host CPU to do most of the work associated with their particular tasks, but because of this they add a negligible amount to the final cost of the motherboard. 

·        Integrated Hardware Monitoring – Once again, by integrating hardware monitoring onto the 686A South Bridge, VIA helps to cut motherboard manufacturing costs by removing yet another chip from the PCB.  Most motherboards use an external chip to provide hardware monitoring functionality which takes up PCB space and adds the cost of the chip to the motherboard.  The integrated hardware monitoring can monitor 5 voltages (including the voltage supplied to the 686A chip itself), three temperatures (including the temp of the 686A) and two fans. 

·        Universal Serial Bus Controller – The 686A’s USB controller goes one step above Intel’s current USB implementation by allowing support for up to 4 USB devices. 

In the end, the 686A South Bridge helps to integrate three commonly external chips (I/O Controller, Hardware Monitoring Controller, and South Bridge) into one chip.  This helps to bring the cost of motherboards based using the 686A down to costs lower than what the implementations based on the 596B placed them at.  The 686A is a better overall solution than the 596B for a motherboard manufacturer yet there are still some motherboard manufacturers that use the old 596B South Bridge.