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As I see it it really is too expensive for the results you would get (unless you are accessing lots of data in a sequential manner which is not usually the case in multitasking environments).

The article is about PC133 mostly. Yes, RDRAM is more expensive than other kinds by a large margin - for now. The news of the past few weeks indicates that it won't be for much longer.

If you have a computer that is using an 820 chipset, it will perform just about as well as one equipped with the faster SDRAMs. That is for one channel moving 8 bits at a time. The 840 chipset results in much better performance.

All this is beside the point. This is the first generation of RDRAM, and the processors it is tied to are being retrofitted with control chips. Those processors are designed to work with SDRAM, so the fact that you see any performance improvement at all going to a completely different architecture is interesting.

You start to get better, more tangible performance gains (theoretically) when the processor is designed and optimized to the Rambus memory. Right now, we are limited by 133MHz and 200MHz external busses on the current generation of processors. Already you have a 3 or 4 to 1 disparity in the speed of the processor and the maximum speed of the memory, and they need a design change to fix it!

The other big issue is the future. You can't scale the SDRAM technology from 133MHz to 266MHz to 532MHz to 1064MHz... forever. The technology just isn't designed for that. You can, however, parallel 8 RDRAM channels to get 64 bits at 800MHz today. In a year or so, you will be able to get 4 times that. Direct to the processor.

Of course, the processors won't be able to handle those kinds of data rates for a while, but having a 1GHz processor running on a 200MHz bus is a real shame. What will we do at 10GHz?

Latency will continue to be a bigger and bigger problem for all technologies. At 10GHz, the electrical impulse can only travel about 6/10 of an inch. This is discounting completely line capacitance and signal rise/fall time. RDRAM has excellent latency characteristics when compared with other technologies. If you want links to a white-paper that goes deeper, mail me. It will only get better when it does not have to go through a controller chip - i.e., the controller is built in to the processor and RDRAM talks directly to the L1 cache.

So what about now? Go to and look at the performance benchmarks. Wait! Before you think that they are somehow rigged, you should know that Tom's has done the same set of benchmarks and they look remarkably similar to what you see on the Rambus site.

The one thing about Tom's is that they compare it to an early brassboard-motherboard with DDR (no pictures, alas). The benchmarks for DDR and RDRAM with 840i chipset are virtually identical. However, Rambus is currently in court challenging DDR - apparently they think it infringes on a number of their patents (4 that I know of). If they win the case, they get to collect royalties on DDR as well.

Why do RDRAM and DDR have the same performance specs? Because DDR is designed to maximize performance on a 200MHz front-side bus (different on different processors, but just assume 200, okay?). The 200MHz bus is a bottleneck, but these processors were designed for slow memory. No one thought it would be a good idea to have a 32-bit 800MHz bus on an 800MHz processor, because at the time the memory did not exist. Give the processor designs a little time to catch up, and give RDRAM a little time to come down in price.

Why RDRAM now? Why not some other technology? Good question. I own the stock, but I will not rush out to buy an 820i board when I could get comparable performance out of fast PC-133 memory. I might buy an 840i board after the prices settle a bit. Remember, this stuff is still not even in full production yet. Supply goes up, meets demand, prices drop. I expect RDRAM to eventually reduce the cost of a system while still providing performance as good as or better than anything else on the market.

However, the Japanese are rushing to buy an RDRAM device - the new Sony PlayStation II. Why RDRAM? Two chips instead of 8 or 16. Rambus estimates this saves Sony anywhere from $30 to $50 per unit shipped. I don't currently own a gaming system, but I will be in line this summer to get one of these. PlayStation II is going to be huge, and Rambus gets a couple of bucks for every unit sold.

In the next year, look for RDRAM to drop in price to the point where it is within 10% of PC-133. Also look for it to be used in cheaper computers and desktops. I am still trying to find hard numbers on these issues, but I will be posting them to the RMBS board as soon as I find them.

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