Thanks xStainDx. Advanced Micro Devices Incorporated goes Intel route these days when it obliges end-users to acquire expensive registered PC3200 DDR SDRAM memory modules for AMD Athlon FX-51 microprocessors. The company, however, does not pin any illusions on registered memory modules, as next year it plans to launch another version of its chips with integrated memory controller supporting ordinary DDR SDRAM memory modules even in dual-channel mode.
In Fall 1999 Intel Corporation, Santa Clara, California, unveiled its Pentium III "Coppermine" processors with i820 (Camino) chipsets with RDRAM memory controller. It was clear, PC600, PC800 RDRAM memory was not necessary for Intel Pentium III CPUs and very few users utilized Intel's RDRAM supporting P6 platform. One year later, in November 2000, the Santa Clara, California-based chip-maker launched its Pentium 4 processor and i850 chipset with only RDRAM support. RIMMs have always been the most expensive memory modules and even enthusiasts did not want to adopt them. Furthermore, RDRAM and supporting platforms were not able to show tangible performance increase over the less expensive AMD Athlon as well as Intel Pentium III with PC100 or PC133 SDRAM. What is happening now? AMD tries to go the same route by forcing to use expensive PC3200 registered DIMMs with its desktop AMD Athlon FX-51 processors.
Registered memory modules are used in variety of server applications and AMD Athlon 64 FX is the first desktop platform that requires this type of memory. Basically, registered and buffered memory modules allow installing a lot of memory modules on one a single memory channel – a not really necessary capability for the vast majority of desktop computers. Buffered memory modules are equipped with a special chip called "register". This chip clocks in and clocks out the data by system clock taking about one clock cycle to perform the registering process. In applications that require registered RAM modules such logic is incorporated into the memory controller design.
News source: Xbit Labs - AMD Goes Intel Route?