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Improving a Classic - VIA's KT266A Chipset for AMD-based systems

Improving a Classic - VIA's KT266A Chipset for AMD-based systems

The computer industry often uses letters such as "A", "B" and so forth on model numbers to indicate fairly minor improvements. That's not the case with VIA Technologies's new KT266A chipset for high-speed Athlon processors. While the KT266A is based on VIA's original KT266 DDR-SDRAM chipset introduced in the Spring of 2001, the KT266A blows the doors off its predecessor because of its improved memory subsystem.

Performance Driven Design - More than Just a Slogan

VIA Technologies replaced the unimpressive memory controller in the KT266's North Bridge (the VT8366) with a greatly improved design in the new North Bridge chip (VT8366A). The new memory controller is referred to by VIA's block diagram (available at VIA's web site) as "Performance Driven Design". Technically speaking, this name sums up a lot of changes, including:

  • double the burst rate for memory transfers
  • deeper read-write internal memory buffers (also called data queues)
  • faster memory timings

This improvement in the memory controller (Tom's Hardware calls it the "industry's fastest DDR memory controller") is the major change in the KT266A over the KT266, and takes care of the major weakness in the original design.

Faster Memory Control Unleashes Other Great Features

Now that the KT266A's memory controller can take full advantage of faster DDR SDRAM, the rest of the chipset's features (unchanged from the original version) can be fully appreciated:

  • VIA's V-Link Hub architecture runs the North Bridge/South Bridge connection at double the speed of older chipsets: a 266MBps dedicated connection versus the normal PCI bus 133MBps connection (shared with adapter cards and IDE hard disk interfaces)
  • Support for both 200MHz and 266MHz DDR SDRAM for maximum performance
  • Support for PC133 and PC100 SDRAM for economy systems
  • Support for both AGP4x and AGP2x video cards

The KT266A can be used with both Athlon and Duron processors running a wide variety of video and memory configurations, so you can build an economy system with older AGP 2x video cards and a Duron or a fire-breathing AGP 4x system that uses a fast Athlon processor.

Modular Chipset Design Pays Off

Traditionally, new chipsets have required new motherboard printed circuit boards to be produced to handle the pinout changes. The KT266A uses the same pinout as its predecessor, the KT266, for both North Bridge and South Bridge chips. VIA's Modular Architecture Platform (V-MAP) design philosophy is the reason. This enables motherboard makers to switch production to the KT266A chipset without scrapping already-produced motherboard printed circuit boards, and it has a second benefit: interchangeable South Bridge chips. Some vendors will opt for the original VT8233 South Bridge, while others will switch to the new VT8233C with its built-in 10/100 Ethernet controller (perfect for broadband Internet or home networking).

South Bridge Features

The South Bridge chips used by the KT266A remain the same as with the KT266. The VT8233 South Bridge supports ATA-100 IDE hard drives, six PCI slots, six USB ports, ACPI and APM power management, and support for AC 97 audio, MC97 soft modem, and an optional ACR riser slot card. The VT8233C has all the same features, plus it adds a 3Com 10/100 Ethernet adapter.

KT266A Sounds Better - But Is It?

Benchmark testing reveals that the KT266A is worth asking for by name (and by letter). AnandTech's mix of theoretical, business, and gaming benchmarks shows that the KT266A beats its older sibling by 48% in the SiSoft Sandra STREAM memory test (a synthetic memory benchmark), by 7-10% in business applications, and by 15% in enterprise computing tasks. Want to play a game? If you're running a KT266A-based system, you'll probably win, thanks to a 15% improvement over the KT266.

Getting Your Hands on KT266A-based Motherboards

VIA has made it as easy as possible for motherboard vendors to switch to this new chipset, but it will take a while for everyone to get on board. The VIA Technologies' "DDR Motherboards Based on VIA Apollo Chipsets" page http://www.via.com.tw/jsp/en/products/apollo/ddrmobo.jsp is a great place to start. It lists vendors and model numbers for motherboards using both the KT266 and the new KT266A chipsets. Read this list carefully to make sure you get the performance you want when you buy your motherboard, since many vendors still sell motherboards based on the original KT266 chipset.

Web Resources

Compare the disappointing performance of the original KT266 to the brilliant KT266A with these articles from Tom's Hardware:

KT266 (original)

New KT266A

Get AnandTech's ruminations on why the KT266A is so much faster than its predecessor:

VIA Technologies' official KT266A website, with links to more reviews and other information is at:

Learn more about SiSoft Sandra, an amazing system reporting and benchmarking tool that can help you get more performance from any hardware at: www.sisoftware.demon.co.uk/sandra/start.htm

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