KT133A: The Final Version of KT133?

The KT133A chipset is composed of two parts, the 8363A North Bridge and the 686B South Bridge. The 8363A North Bridge is exactly the same as the 8363 North Bridge used in the KT133 chipset, except that it has official support for 133MHz FSB operation. With the original KT133 chipset, FSB overclocking was generally not a viable option since it couldn't be pushed any higher than 110MHz - a mere 10% overclock. Therefore, although most manufacturers provided FSB speeds of as high as 166MHz or more, a large portion of these speeds were useless for overclocking.

Fortunately, the new 8363A North Bridge is designed to run at 133MHz and can run reliably at 160MHz or above. You may wonder why VIA did not just support 133MHz FSB from the beginning, and that would be a very valid question. VIA's answer was that they did not want to give too much room for overclocking, so they disabled something in the chipset to prevent such high speed operation.

The increased usable range of FSB speeds gives us a lot more flexibility when it comes to overclocking. In the past, you had to rely mostly on multiplier overclocking, but there is a lot of performance to be gained from faster FSB speeds. With the new KT133A chipset, users can now raise the FSB speed higher and lower the clock multiplier to boost performance noticeably without actually raising the core clock of the CPU.

Like the older 8363 North Bridge, the 8363A chipset also support AGP 1X/2X/4X, so most manufacturers have included universal AGP slots. That means that the AGP slot is not keyed for 1.5V or 3.3V AGP cards only, so you should have no problem installing just about any AGP video card. Some manufacturers have gone a step further and included AGP Pro slots, which follow the same performance specifications, but provide additional electric current for high-end video cards.

The new 686B South Bridge is pin compatible with the older 686A, with the difference between the two being the addition of Ultra ATA 100 support on the 686B. Although at this point no hard drive has a sustained transfer rate of higher than 66MB/sec, it's only a matter of time before hard drives pass this barrier, at which point Ultra ATA 100 will become a more important feature.

Also like the 686A, the 686B features two USB root hubs, supporting a total of four USB ports. Two traditional USB ports are usually mounted at the back of the board within the ATX I/O panel, while a header for the second set of USB ports are usually located on the left side of the motherboard. You'll need a USB bracket to take advantage of these ports, but fortunately manufacturers have started to include such a bracket in the box.

Index What to look for in a KT133A motherboard
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