Intel Developer Forum Conference - Spring 2001: Part 1

More Pentium 4s = More RDRAM

Intel is still strongly touting their belief in RDRAM, which is actually proving to be useful with the Pentium 4.  Rambus is definitely in the middle of some very interesting legal situations, but we're not evaluating legal practices here so we'll focus on what their technology is hoping to bring to Intel and what it is already doing.

It is only in fair journalism that we present the fact that RDRAM has come down in price.  The big argument when RDRAM was released was that its price was entirely too high while Rambus argued that it would come down.  Well, it has and so has the price of DDR SDRAM as well although it didn't start at nearly as high of a peak as RDRAM. 

The above graph shows data comparing PC800 RDRAM prices to PC2100 DDR SDRAM prices from our Weekly Motherboard & Memory Price Guides for the past 8 weeks.  We did not include the price of PC133 SDRAM because contrary to what promoters of both technologies (RDRAM & DDR) have promised, neither memory technology can touch the extremely low prices that PC133 SDRAM is going for. 

The peak that DDR SDRAM held at the end of last year and in the transition to this year was what Intel was quite happy about since they were finally able to say that RDRAM was cheaper than DDR SDRAM.  The case now is that both technologies are approximately equal in price and neither happens to be competitive with PC133 SDRAM prices, yet.

Intel continued to speak of their commitment to RDRAM for their desktop line of processors, with PC133 SDRAM being used on all of the low end and entry level systems.  If you haven't guessed already, Intel's stance on DDR SDRAM hasn't changed much either.  They are examining it as a viable solution for servers, however its position in the desktop market is questionable.  From Intel's perspective, if the prices of RDRAM continue to drop, DDR doesn't make sense as a production avenue since the dual channels of RDRAM on the i850 chipset boast a lower chipset pin count and thus fewer traces on current Pentium 4 boards.

But before you can go off and praise RDRAM's lower pin count (the bus is still only 16-bits wide compared to DDR SDRAM's 64-bit wide bus), a promise that Rambus made a while ago has yet to come through.  According to Rambus, one of the benefits of RDRAM technology was that it would allow motherboard manufacturers to continue to use 4-layer motherboards because of the fewer traces required between the memory banks and the Memory Controller Hub (essentially the Northbridge).  However all currently shipping Pentium 4 boards are 6-layer designs, we got confirmation of this by speaking with motherboard manufacturers on the topic. 

Intel is working with memory manufacturers in order to help tweak their RDRAM designs so that they may eventually switch to a 4-layer design, but that promise has not held true yet.  For comparison, the majority of KT133 and KT133A motherboards are still 4-layer designs (and are thus cheaper) while all AMD 760 designs are 6-layer. 

Lowering RDRAM cost is definitely in Intel's best interest, and they are working with Rambus and memory manufacturers to do that.  In 2002 a new form of RDRAM will be introduced, known as 4i.  The 4i denotes 4 independent banks that make up the actual RDRAM module.  The current form of RDRAM is defined as 2x16d or 16d, the d denoting dependent and the 16 referring to 16 dependent banks.  The main benefit Rambus hopes to gain from moving to 4i is a decrease in die size, thus decreasing overall memory cost.  A side effect of how RDRAM 4i's bank layouts are done results in a limitation of RDRAM being avoided.  Normally with 16d RDRAM, adjacent banks cannot be accessed at the same time due to adjacent banks sharing each other's sense amps.  The 4i bank layout changes things around slightly by only using 4 internal banks which can all be accessed independently by making use of dedicated sense amps for each bank.  Intel downplayed the performance penalty or gains that would be associated with the move to 4i.  We can say that 4i RDRAM modules will require chipset support, and their release in 2002 will be accompanied by the release of Intel's second RDRAM chipset for the Pentium 4. 

Apparently yields on PC800 RDRAM have improved dramatically since we last visited the issue.  Intel claims that memory vendors are even considering higher frequency parts, such as PC1066.  If Intel were to increase the FSB on the Pentium 4 next year, PC1066 may be the perfect complement.