VIA's P4X266A
The P4X266A is VIA's second spin of its DDR-capable Pentium 4 platform. We came away with very positive impressions when we tested the original P4X266, and those impressions were only reinforced by our experience with Shuttle's excellent AV40R motherboard. Given the P4X266's snappy performance, we were a little surprised to see a new revision of this motherboard make it out the door so soon.
OK, so I should have pulled off the heatsink. But look: cool logo!
However, the changes make perfect sense. VIA substantially upgraded its KT266 chipset with the improved memory controller in the KT266A. The P4X266A brings that same enhanced memory controller to VIA's Pentium 4 offering. Tighter timings in this controller help increase bandwidth and lower latencies. This revamped memory controller is the fruit of VIA's "performance driven design" initiative. We'll see whether it lives up to the name.
The P4X266A also includes an enhanced processor bus, which should help the P4X266A keep up as Pentium 4 clock speeds rise. This new processor bus has an IOQ depth of 12, just like Intel's 845, and it can keep up to 13 instructions "in flight" at once. VIA claims the P4X266A incorporates "support for future bus speeds"—presumably 533MHz, which is the next stop on the Pentium 4 bus speed bandwagon.
Last and probably least, in addition to the new P4X266A north bridge, there is a new VT8233A south bridge chip that supports ATA/133 devices. Unfortunately our test motherboard came equipped with only the VT8233 south bridge—not that we have any ATA/133 drives to test with just yet, anyhow.
VIA's cheesy block diagram shows just where the enhancements fit in
I should mention that our P4XB-S P4X266A test motherboard is a VIA-branded consumer product, one of the first out of VIA's new Platform Solutions Division. VIA created the PSD in order to make sure products like the P4X266A could reach the market even in the face of obstacles like legal threats from Intel. Of course, that's not the only reason. Intel has done the same thing, supplying the market with Intel-branded motherboards, for quite a while now. Doing so establishes a nice baseline for products based on one's chipsets, so it makes sense.
The P4XB is a surprisingly solid first effort from VIA PSD. It includes three DIMM slots, five PCI slots, a range of menu-drive overclocking options, a secondary Promise IDE controller, and C-Media's popular 8738 audio chip. Component placement on the board is sensible, and I didn't find any major annoyances when working with it, save one.
VIA shipped the board out to reviewers with a "performance BIOS" set to default to 1T command rate for memory. Pure and simple, the P4XB-S was not stable for me at 1T command rate—not with a CAS 2 Micron DIMM, nor a Corsair, nor a Micron DDR333 DIMM. Once I resorted to the 2T command setting and loosened up some of the other timings settings in the BIOS, the P4XB-S ran fine at CAS 2. I assume the board won't ship to consumers with a BIOS that defaults to a 1T command rate.
