fkloster, I disagree that the P4 needs serial memory to perform well...from the perspective of the CPU, the only thing that matters is bandwidth and latency. The P4 is said to perform well with DRDRAM simply because it was designed assuming that the higher latency DRDRAM would be used with it; the dual Rambus channels on the i850 and the P4's hardware prefetch hides much of the latency.
IIRC, any DRDRAM read operation requires 16-bytes, so after the initial address is applied, eight sequential words of 16 bits each are transfered serially down the bus in a burst. The data gets parallelized in the memory control using 16 8-bit wide shift registers before it gets sent to the CPU.
The data
has to be parallelized sometime...it's a simple fact that operations in hardware are performed
much faster in parallel than serially. In digital logic design, serial arithmetic hardware is often taught first because it's design is relatively simple, whereas parallel units are sometimes more complex and less intuitive to design. But what would you rather have in your CPU, a serial non-restoring multiplier that takes 96 clock cycles (96 ns at 1 GHz) to do a 32-bit multiply, or a 5-level carry-save Wallace tree that does the same operation in 17 logic gate delays (around 1ns given today's transistor technology)?
Serial makes sense for high-speed buses (such as Rambus, Serial ATA, and Hypertransport), but CPUs will always be parallel. After all, Intel plans to use IA-64's EPIC architecture for the next 30 years, which explicitly defines the parallel execution of instructions in the instruction set.
That being said, I still think that the i845 is a dead-end product....PC133 simply cannot provide enough bandwidth for the P4, and if/when the platform supports PC2100, it probably won't have enough bandwidth for the latest and greatest P4. To address the original question, I really don't think Intel is releasing the i845 mearly to make DRDRAM look better than SDRAM...it doesn't really make any business sense to purposefully release a bad product simply to make another one of your products look good. Evidently Intel believes that they can boost low-end P4 sales with the i845, and that's why they're releasing it.
A Crush chipset for the P4, on the other hand, would be different...it has a large amount of bandwidth, and it's crossbar/dual memory controller configuration can reduce latency and increase efficiency like the dual-channel Rambus on the i850.
Of course, all this could change if the rumors that Northwood will have an integrated DRDRAM controller are true.
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