PC4200 is now available, that does not indicate you can or should purchase this RDRAM spec for use in your i850(e) or SiS's 645xx offerings you may own or recently purchased. While the PC4200 spec does offer some obvious benefits over previous RDRAM specs, it has some significant difference from previous RDRAM specs.

PC4200 is also notched differently that PC800/1066. Essentially PC4200 is a design that incorporates 2 RDRAM modules onto one module. This provides a less expensive manufacturing process for motherboard makers, as well as some other benefits. Intel is just now concluding their validation of PC1066 RDRAM modules for use with the i850E chipset, along with announcing new chipsets for the P4. More information on the validation process can be found here. You may want to read this article at Tom's, that discusses the difference in 16-bit and 32-bit RDRAM design as well as some of the key points to remember/know when considering the latest RDRAM designs.

Of course there is a large amount of information available from Rambus's own memory overview if you can read beyond PR.

The real issue is to make absolutely certain your system (Motherboard) can and does support the type of RAM you want to or already have purchased. As in the case of PC4200...simply having a i850e chipset motherboard DOES NOT indicate you can use PC4200 RDRAM, as the design of the module is physically different from previous RDRAM.

Currently the Only motherboard I am aware of being available that accepts PC4200 (1066MHz) RDRAM is the Asus P4T533.

This board also has some notes* you should read

most significantly regarding the Asus P4T533 :

Note: * Use only the tested and qualified 32-bit 1066MHz RIMM listed below.
Other RIMM manufactured by other vendors may not be suitable for this motherboard.

The naming scheme used by RAMBUS is confusing to say the least. The articles linked to here help to clarify the specs, and how to determine how the various RDRAM modules can be identified, their specs, and potential performance. The last aspect clearly depends greatly on the chipset used, as well as requirements of the applications being used. Please keep in mind that benchmarks are not a "promise" of how a component will perform for you. Real world results are subjective, and benchmarks should only serve to provide a "feel" or "ball park" potentials for a given component.

Ray Griffith