AMD Athlon "Thunderbird" 1 GHz / 800 MHz

So if the VIA KX133 doesn't officially support the Thunderbird, then what chipsets do?  Aside from the original AMD 750 chipset, VIA does have a Socket-462 version of their KX133 chipset, the KT133.

The KT133 is exactly the same as the KX133 chipset in that it uses the same memory controller, the same AGP controller, and basically is the same North Bridge with slight timing modifications to support the Socket-462 Thunderbird processor. 

VIA will be releasing a version of the KT133 chipset with a Savage4 AGP device integrated into the North Bridge of the chipset.  As far as we know, this will be called the KM133 chipset and it's pin compatible with the KT133's North Bridge.  The KM133 also features an on-board AGP 4X slot, so that, if you're not going to use the integrated Savage4 graphics, you can simply stick in a regular AGP (or PCI for that matter) video card and it will disable the integrated device. 

For those of you that need a refresher on what features the KX133 and thus KT133 chipsets support, let's take a look at the explanation behind the specs of the North and South Bridges that the chipset uses:

The KT133 uses a slightly different North Bridge than the KX133, the 8363 instead of the 8371 that's a part of the KX133 chipset.

·        High Performance Athlon CPU Interface – All that this fancy statement means is that the 8363 interfaces with the Socket-A connector on the motherboard using the Athlon’s EV6 bus.  This interface is the "200MHz FSB" that most Athlon motherboard manufacturers throw around when it’s actually a 100MHz Double Data Rate FSB.  This implementation remains relatively unchanged from the original AMD 751 North Bridge, meaning that the amount of available bandwidth has not changed (1.6GB/s).

·        Fully Featured Accelerated Graphics Port (AGP) Controller – The 8363’s integrated AGP controller is actually borrowed from VIA’s 694X AGP controller in that they both feature the same core.  The controller features support for AGP 1X, 2X and 4X transfer rates, and because of its AGP 4X support, motherboard manufacturers can choose to implement an AGP Pro connector on motherboards based on the KT133 chipset.  This is an improvement over the AGP 2X limitation of the AMD 751 North Bridge.

·        Concurrent PCI Bus Controller – The integrated PCI controller is the same as the 694X’s (Apollo Pro 133A) PCI bus controller.  It supports 5 PCI master devices, but motherboard manufacturers can implement more than 5 PCI slots, the added slots will simply be slave devices.  Nothing special here.

·        Advanced High-Performance DRAM Controller – The Memory subsystem of the KT133 is the biggest difference between the 8363 North Bridge and the AMD 751 North Bridge.  The 8363 can address up to 8 RAS lines, meaning motherboard manufacturers can outfit their boards with up to 4 DIMM slots with support for double sided DIMMs in all of the slots. 

The memory controller, once again, very closely resembles that on the 694X (Apollo Pro 133A), especially in the supported memory types.  The 8363 currently only supports PC133 and PC100 SDRAM (no DDR SDRAM support) as well as VC133 and VC100 Virtual Channel SDRAM support.

The memory bus can operate (officially) at either 100MHz or 133MHz, which is an improvement over the sole 100MHz setting present on motherboards based on the AMD 750 chipset.  Keep in mind that we’re talking about the memory bus frequency, not the front side bus frequency, the latter which operates at 100MHz DDR regardless of the frequency of the memory bus.  The 133MHz memory bus frequency allows the KT133 to attain an available 1.06GB/s of peak memory bandwidth, up from the 800MB/s on the AMD 750. 

The chipset itself supports up to 2GB of memory, but it’s up to the motherboard manufacturers to make sure that their boards can reach this capacity properly without sacrificing stability. 

The 686A was first introduced on the Apollo Pro 133 chipset but is referred to as an option on the old Apollo Pro, a P6 chipset, as VIA’s Super South Bridge, this of course being an improvement over the 596B regular South Bridge.  The 686A has been paired up with the 693 North Bridge for use with the Apollo Pro+, again with the 693A North Bridge for the Apollo Pro 133, and once again with the 694X North Bridge of the Apollo Pro 133A. 

The flexibility of VIA’s North/South Bridge setup is one reason they have kept it around for so long, and it has allowed them to use the 686A on their two Super7 chipsets, the MVP3 and the MVP4. 

On the Athlon side of things, the 686A was the replacement South Bridge for the AMD 756 in some designs that implemented the AMD 750 chipset.  The 686A was then featured on the KX133 chipset and now on the KT133 as well.

The 0.35-micron, 352-pin 686A remains unmodified from its original introduction and use on the P6 chipsets, and thus the specs remain the same.  Let’s discuss the benefits of each one of these features to see what they actually accomplish:

·        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 – Just recently, Ultra ATA 33 has 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, but 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 – KT133 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.