A novel scheme employing two low-cost double-data-rate (DDR) devices can inject twice as much performance into a memory module, delivering the equivalent of DDR533 using DDR266 memories. Developed by Kentron Technologies, quad-band memory (QBM) technology is being offered as an industry standard to improve the memory subsystem performance for fast CPUs. The QBM scheme boosts performance by taking data bits from one of the devices with a normal clock and the data bits from a second device with a 90° delayed clock. A QBM module then actually generates four bits per clock cycle. A normal DDR module provides only two bits per cycle.
It's possible to implement QBM dual-inline memory modules (DIMMs) at minimal additional cost by leveraging low-cost commodity DDR DRAMs, an advanced technology switch component, and a clocking device that generates the "bit-packing" clock. The DIMMs fit the same connectors as DDR modules, allowing for simple system upgrades. The host system also must be upgraded, since the motherboard chip set and BIOS must be QBM-enabled.
VIA Technologies has already committed to developing a QBM-enabled motherboard chip set, while STMicroelectronics will devise the QBM switch element. Integrated Circuit Systems has come up with the phase-locked-loop timing device. Over 23 companies are part of the QBM Alliance, which has outlined plans to offer QBM modules with speed grades of 533 MHz using DDR DRAMs and 800 and 1066 MHz using DDR2 memories.