First of all, let's get to know the basics of how this memory type works. As it is based on DDR, we will just point out its differences from DDR.

As is known, the number of banks, i.e. logical units, which are used by the CPU for chips access, is an even number. QBM (Quad Band Memory) technology unites these memory banks into pairs. The signal of the first bank is in phase with the controller clock, while the second bank has a phase difference of 90 degrees from the first clock. Here we will need a helping hand from a special switch called QBM10. It will identify which of the two banks is being accessed by checking the phase.

Delving deep, QBM10 is a combination of a 10-bit 2-to-1 switch and a 10-bit register, which distributes the controller workload more evenly, reduces the execution time of some operations in the work cycle and improves charge/capacity ratio. There are also some nice trifles like the doubling of the correctness window during writing operations, that is the time interval when the data sent to the memory module by the chipset are still considered correct.

In fact, all these functional units are quite simple, so QBM10 is simple and not expensive, too: 48 pins, 7x7mm area. It's just a small drop lost against the background of a TSOP-packaged DRAM chip. On the other hand, eight switches like that plus an additional frequency generator are necessary for a standard unbuffered DIMM module. So, it all may amount to a high total. But we will talk about the price of the solution later on.

Of course, we can't move along just putting switches into memory modules. Chipset's support is also required and this is where similar initiatives from various companies usually tripped over.

Intel still plays the main role here holding a considerable share of the chipset market. Moreover, Intel has always been advancing the industry. The Rambus affair is not enough to break this tradition. But, Intel isn't eager to promote QBM. Among well-known manufacturers, only VIA and SiS support this memory type. In fact, SiS is far less active than VIA.

Actually, VIA's position is quite understandable. The company doesn't sit at the curbstone of the world progress, but watches closely all emerging technologies. VIA just sticks to another ideology: they don't push ahead and put up industry milestones, but develop available technologies to their maximum price-to-performance ratio. That's what we saw when Intel staked on Rambus, and VIA - on PC133 SDRAM.

Today both companies unanimously supported PC3200 DDR SDRAM. Of course, there is a question of where to go now. This memory type will last quite long with Athlon XP, while Pentium 4 lacks the bandwidth already. The first possibility of the three, which we have already discussed above is simply unreal: DRAM makers just can't increase the frequency any higher because of their current technological capabilities. Intel chose the second way and has already started shipping dual-channel DDR chipsets. Well, the company had already gone this way before in its i840 chipset, although it supported dual-channel Direct RDRAM.

This approach seems advantageous for today, that's why SiS and VIA also started producing dual-channel DDR chipsets. Firstly, two PC3200 channels exactly meet the requirements of 800MHz FSB for future Pentium 4 (that's exactly why Intel reconsidered its attitude to this memory type): 8x800 = 6.4GB/s. Secondly, there is no need to push the memory makers any more: no new controllers, no changes of the technological process are necessary. Moreover, all already manufactured PC3200 modules are also guaranteed to provide the desired 6.4GB/sec.