While the 850E chipset offers 33% more FSB bandwidth, memory bandwidth remains unchanged. The chipset still officially uses PC800 RDRAM, delivering 3.2 GB/s.
In order to keep things synchronous, the RDRAM clock was increased along with the system clock, and the RDRAM multiplier simply lowered. With a 400 MHz FSB, for example, the RDRAM is clocked at 100 MHz, using a 4X multiplier, for an effective 800 MHz (remembering that, like DDR memories, RDRAM transfers twice per clock cycle). When using the new 533 MHz FSB, the RDRAM will likewise operate at 133 MHz, but use only a 3X multiplier, resulting in the same 800 MHz effective speed.
In addition, when using the 533 MHz FSB, the 850E chipset requires RDRAM with a core access time of 40ns, while at 400 MHz, 40ns, or the standard 45ns RDRAM is acceptable. 40ns RDRAM is fairly widely available already, and should not present any real obstacle. Furthermore, in our own testing, 45ns memory operated perfectly, although this is not an officially supported configuration.
Unofficially, in fact, the 850E does fully support PC1066 RDRAM. It’s simply that, at this point in time, there’s not enough volume of PC1066 for Intel to validate and support it on paper. In our own experience, the 850E chipset is fully capable, performance and stability-wise, of running PC1066 RDRAM, and in fact, if one was to load an 850E board with PC1066 memory, it would detect it and operate flawlessly (when we inserted PC1066 into our D850EMV, the board produced a warning indicating that it was not a supported configuration, but then proceeded to operate flawlessly at PC1066 speeds). It’s simply not officially supported by Intel at this time.
We expect some third party motherboard manufacturers to document and make that functionality known to enthusiast consumers, however, and we’d expect to see PC1066 RDRAM becoming available in a few places as well. However until Intel fully validates and supports PC1066, this will certainly remain an ‘enthusiast only’ option, and not something you'll be able to order from OEMs like Dell.
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