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 VIA KT133A.The VIA KT133A was released at the very tail end of 2000 to provide support for AMD’s 133 MHz FSB (266 MHz DDR) Athlon processor. Essentially it is an upgrade to the KT133 design as it added in a new Front Side Bus speed of 133 MHz, as well as a number of minor improvements over the KT133. Whilst both the KT133 and KT133A chipsets are manufactured in parallel, emphasis amongst motherboard manufacturers and systems integrators appears to be gradually moving towards the KT133A, with most new releases appearing on this chipset. Chipset Design.Like the KT133 the KT133A can be described as being a “classic” chipset design being based upon a North and South Bridge layout which uses the PCI bus as the main connection between the two chips. Essentially the KT133A is a similar design to the Apollo Pro133A, but VIA removed the GTL+ bus interface and replaced it with the Alpha EV6 bus as used by the AMD Athlon family of processors. This is probably the biggest difference between the Pro133A and the KT133A as the EV6 bus is more advanced than its GTL+ counterpart. Unlike the GTL+ the EV6 can read and write from the CPU to chipset at the same time by using two 100 MHz channels, essentially making it a DDR (Double Data Rate) chipset. Both of these 100 MHz channels gives the EV6 an equivalent performance of a 200 MHz SDR (Single Data Rate) bus such as the GTL+. The use of a DDR bus such as the EV6 helps to increase the bandwidth between the CPU and North Bridge controller. As the Athlon range uses either a 100 MHz FSB (200 MHz DDR) or 133 MHz FSB (266 MHz DDR), these are the main supported bus speeds. The memory controller on the KT133A is similar to that on the Apollo Pro133A and KT133 as it gives usersthe ability to clock the memory bus at a different speed to that of the main CPU bus. Users of the KT133 can for example run a 100 MHz FSB Athlon (200 MHz DDR) with memory clocked to 133 MHz to gain full advantage of PC-133 SDRAM, or usets could still use any existing PC-100 SDRAM with the same 100 MHz bus Athlon (200 MHz DDR). The only downside of this feature is that it increases the time taken by the memory controller on the chipset to read and write from main memory. One of the areas where the KT133A has been praised is its ability to gain impressive bandwidth’s when running a 133 MHz FSB Athlon with PC-133 SDRAM, with many commentators stating that memory performance is on a par with that of the AMD 760 chipset.
As the KT133A is more recent than the KT133, it has been mainly paired to the VT82C686B which supports U/DMA 100 Hard Drives on top of the
existing support for U/DMA 33 and 66 drives.
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