VIA Apollo KX133 Athlon Chipset - Part 1

While it is true that the 1.06GB/s of available peak memory bandwidth provided for by the PC133 support of the KX133 is a great improvement (33% to be exact) over the 800MB/s provided for by the PC100 support of AMD’s 750 chipset, it still isn’t enough. 

With AGP 4X capable of transferring up to 1.06GB/s of data to/from system memory and the peak available memory bandwidth equal to that number, factoring in memory bandwidth required by the CPU and other parts of the system, PC133 support isn’t enough. 

The true answer to this problem lies in Double Data Rate SDRAM, or DDR SDRAM for short.  As we know from previous articles, DDR SDRAM works much like the AGP bus and the Athlon’s EV6 bus by transferring data on both the rising and falling edges of the clock.  By doing this, a 100MHz DDR SDRAM module can actually do twice as much work per clock cycle, offering a peak bandwidth figure equal to that of a regular 200MHz module. 

From a pricing standpoint, DDR SDRAM costs barely  3 – 5% more than regular SDRAM.  The only thing the market is waiting for is availability of DDR SDRAM chips.  We have already seen them used on some graphics accelerators based on NVIDIA’s GeForce processor, it won’t be long until we see them used on desktops.  Unfortunately, since DDR SDRAM requires additional signaling pins to interface with the memory controller, the 371 North Bridge and all KX133 motherboards that support regular SDRAM won’t support DDR SDRAM.

A DDR SDRAM Module

Micron's DDR Solution

When will a DDR version of the KX133 be available?  According to VIA, their first DDR chipset will be for the P6 bus, meaning that Pentium III owners will get a shot at DDR SDRAM before Athlon owners will.  It won’t be until after the introduction of VIA’s DDR P6 chipset that we will see the introduction of the DDR version of the KX133. 

Micron’s Samurai chipset (P6 bus) already supports DDR SDRAM, and VIA will most likely be licensing the technology behind the Samurai for use in their workstation class DDR chipset (P6 bus).  We haven’t heard any mention of an equivalent chipset for use with the Athlon, but porting the DDR memory controller to the KX133 shouldn’t be too difficult once they get a working chipset in production. 

Chances are that we’ll see AMD’s 760 chipset with DDR SDRAM support before VIA’s DDR version of the KX133 hits the streets.