"Up until very recently registered DDR was a bit of a specialist market, as only high end workstation and server motherboards required it. Also, Intel Xeon based machines run with a Front Side Bus of 400 or 533MHz, which meant that the speed of the registered DDR ram was never going to be more than PC2100, a figure which is dwarfed by modern desktop DDR memory. Nothing seemed set to change this until AMD came along with their Opteron processor, which at that time required registered PC2700 memory installed in pairs to get the most out of the system. However, the Opteron isn't really a consumer CPU, and so none of the major performance RAM manufacturers took any notice of it. But then AMD released the Athlon 64 FX to the masses, which could utilise registered PC3200 in pairs to increase memory bandwidth even further. Suddenly the memory manufacturers had to produce high speed, low latency registered DDR, and this is where the likes of OCZ, Corsair and Mushkin come in."