VIA P4X400 - The little chipset that couldn't
The VIA Apollo P4X400 is one of the most feature rich and powerful chipsets ever produced. DDR333 memory support, offering 20% more memory bandwidth to the CPU,and the ultra-fast 400/533MHz processor bus unleash the full power of today's and tomorrow's Intel Pentium 4 processors, enabling stunning performance across the full spectrum of applications. In addition, the VIA Apollo P4X400 supports the very latest I/O technologies including AGP 8X deriving maximum performance from the most powerful graphics cards and new 8X V-link chip interconnect with 533MB/s of bandwidth between North and Southbridge enabling the processor to exploit the full potential of peripheral devices.
The new VT8235 South Bridge also features first to market innovations including support for six USB 2.0 ports for peripheral connectivity 40 times faster than USB 1.1 and ATA-133 support, the fastest IDE interface available, making total system performance a reality. Additional features integrated into the Southbridge include VIA MAC for 10/100Mbps Ethernet, integrated PCI support, 6 Channel Surround Sound AC'97 audio and MC-97 modem.
The VIA P4X400 strikes me as the little chipset that couldn't. The P4X400 is a re-make of the P4X333, an earlier version that was supposed to bring the first available AGP8x chipset to market, but instead crashed and burned when AGP8x was attempted. Another feature of the P4X400, or lack of feature, is that this chipset was supposed to be able to support DDR-400. However, VIA hasn't been able to get DDR-400 modules to work with their chipset. This has led VIA to only support DDR-333.
Below is an architectural diagram for your reference.