The Northbridge of the KT133 is the VT8363. This chip handles communication with the processor, memory and the graphics card (up to AGP 4X). VIA specifies 100 MHz as the upper limit for the system bus. In practice the VT8363 can deal with a much faster Front Side Bus. Four of the motherboards we tested offer overclocking functions that allow increasing the clock to over 150 MHz. Such settings are a total overkill however. Even though the Northbridge does not have any problems with beyond-spec FSB-clocks, no AMD processor is currently able to handle more than 110 MHz. So to say, most motherboards are equipped for the future, as AMD plans to offer processors with 133 MHz Front Side Bus soon.
The KT133, or VT8363 respectively, allows an asynchronous memory clock. For example at 100 MHz Front Side Bus the memory clock can be set to 133 MHz, which generates a higher performance from PC133-SDRAM modules.
The Southbridge of the KT133 is an old acquaintance. You can find the VT82C686A on Pentium III/Celeron compatible motherboards with the VIA Apollo Pro 133 and 133A as well. Besides the AC97 sound compatibility the VT82C686A also allows the UltraATA/66 mode. VIA is slightly behind with this Southbridge. Intel already offers chipsets with UltraATA/100 support. VIA plans to introduce the pin -compatible VT82C686B shortly, which should also come with UltraATA/100 functionality.
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