Hi all; Pin count reversal: 256Mb RDRAM has 26 more pins than the 256Mb DDR.
Samsung finally has a preliminary spec sheet for 288Mb RDRAM:
usa.samsungsemi.com
Some surprises. The package is a 92-pin uBGA, with a ball pitch of 0.8mm, and all of those pins have to be soldered down, zero NCs. Total package size is 17.6mm x 10.6mm. This is not going to be a cheap package. How is it ever possibly going to be within 10% of the cost of SDRAM?
Speed grades are 600 to 800MHz, no change from present. The data width is still x18. In short, the technology hasn't advanced at all from the previous RDRAM, except that the part has a higher density. The pin count increase didn't buy any advantages at all, same old bandwidth, but worse granularity.
Now we are in a position to compare this against 256Mb DDR specifications.
The Jedec standard 256Mb DDR SDRAM from Hitachi is in a 66-pin plastic TSOP, which is a lot cheaper than RDRAM's uBGA. There are 6 NCs included in the x16 part, lots more in the narrower widths, allowing this pinout to be used for later extensions. The total package size is a little larger (21% by area) than the RDRAM, at 22.22mm x 10.16mm, but since there is room to put 18 of these on a DIMM, the size is not an issue. Clock frequency goes to 143MHz (286MHz data rate), and the same package suffices for the x4, x8 and x16 parts:
semiconductor.hitachi.com
I know that I have stated repeatedly on this thread that pin count isn't what it used to be, so RDRAM being in a package with more pins isn't a big deal. But we have to remember that the whole reason for Rambus' existence is to save pins, what is the industry doing throwing pins away?
The above information on pin counts for the 256Mb packages proves that the industry agrees with me - pin counts on BGA packages are not a significant cost. See my post #reply-13483793 for links to places that will allow you to estimate the cost of pins in various packages. Please note that these facts are in total contradiction to the various amateurs who have been posting on this thread about the great pin savings that Rambus provides.
The simple fact is that the pin count costs that made Rambus a good idea in 1990 are no longer true. Rambus provided an expensive, barely manufacturable solution to a problem that went away. The only thing keeping RDRAM alive now is Intel, but watch what happens this summer.
-- Carl |
