RD-RAM stands for Rambus Direct RAM. Rambus has been in the news many times over the past year. In 1996, it decided to take a radically different approach to memory management for their RD-RAM. They have tried to create the fastest RAM. Some people feel that they were successful, because after all, they do have the fastest RAM when it comes to MHz. The only problem is that they do not have the fastest RAM when it comes to performance. This, combined with a very expensive price tag, has made Rambus very unsuccessful. Even Intel, Rambus' all time supporter, seems to be giving up on it. The early Pentium 4's all had to use Rambus memory. Now, Intel is slowly migrating to SD-RAM, which is expected to take 70% of the Pentium 4 Market. Now that we know some of the background, lets see how Rambus' new approach works.

PC800 RD-RAM Module
© 2001 by www.mushkin.com

Rambus tried to use an approach that has worked for Intel very well. They tried to make the clock speed much faster, so that people would buy their products. In order to change the MHz by an enormous amount, they had to make other parts more inefficient. To make their PC800 Memory run at 400MHz (they have a DDR approach too, and technically, their memory runs at 400MHz), they had to cut down the bus width to 16-bit. If you remember from the CPU history, 16-bit dates back to the 286 era, and even the 386 uses a 32-bit bus. Technically, 1/4 the bus width * 8 times the clock rate would still make RD-RAM transfer twice as fast as PC100 SD-RAM. In order to reduce 32-bit information into 16-bit and then change it back to 32-bit, performance suffers greatly.

As well, Rambus RAM has one of the biggest latency times, making it very inefficient. Rambus RAM is not as fast as a typical PC150 SD-RAM, but the real problem is the price. RD-RAM can be up to 3 times more expensive than standard SD-RAM modules. Here is the impact that RD-RAM's poor latency has on its performance compared to standard SD-RAM:

As you can see, latency is very important in today's memory.

So what has the enormous clock speed done to the temperature of the RD-RAM module? It has brought it high enough that it has to use a heat sink (the blue metal covering up much of the memory you see above is used as a heat sink). Making the clock speed fast before companies do it has some disadvantages. Rambus is not all bad though. It is an excellent concept, and they are very brave to try something new. When you fail, you have to stand up and try again. This is precisely what Rambus is doing. They are working on even higher speeds for their memory modules, and RD-RAM will surely give DDR-RAM a run for its money in the near future.