From Yahoo. Techies comments welcome...
DRAM Design Choices
by: stk_hawk
1/16/00 8:54 pm
Msg: 36356 of 36376
The table below shows the choices an IC designer faces when selecting DRAM in relation to peak bandwidth. An IC
designer has to select a memory architecture that meets performance 1st, with cost running a close second. The table below
also shows the effect of RMBS's recent roadmap announcement of doubling clock rate in the near future. As can be seen
from the table, Rambus has SUPERIOR peak bandwidth performance at each of the bus width nodes.
Memory Type_____SDRAM___SDRAM___DDR_____DDR_____ RDRAM____RDRAM
Clock rate________PC100____PC133_____PC200___PC266_____PC800_____PC1600
Memory Bus
Width
16-bit___________200MB____266MB____400MB___532MB____1.6MB_____3.2GB
32-bit___________400MB____532MB____800MB___1.1GB_____3.2GB_____6.4GB
Memory Bus
Width
64-bit___________800MB____1.1GB_____1.6GB____2.1GB_____6.4GB____12.8GB
128-bit__________1.6GB_____2.2GB_____3.2GB____4.2GB_____12.8GB___25.6GB
Lets take the example of an application needing 1.6GB/s peak bandwidth performance. From the table above, the logical
choices are 128 bit SDRAM PC100, 64 bit DDR PC200, and 16 bit RDRAM PC800. If cost were equal, then the
decision is a no brainer for the system designer. He would go with the lowest pin count solution of RDRAM because this
lowers chipset cost. If the cost is not equal, then the system designer has to speculate what the cost of RDRAM will be in the
future when his system goes into production vs the cost of using SDRAM or DDR at increased bus width.
So why did Sony choose Rambus in PSII? Well if you assume they needed approximately 3.2GB/s bandwidth performance,
their choices were DDR at 128-bits or RDRAM at 32-bits (dual channel). If PC1600 would have been available that would
have also been a possibility. RDRAM was the most attractive solution assuming cost was competitive. To ensure this, Sony
made the deal with Toshiba.
From the table, it is easy to see Rambus has a tremendous technical advantage but to win the battle, they also have to be
cost competitive with SDRAM/DDR at wider bus widths. To insure cost competitiveness, Intel invested $.7B ($.5B Micron,
$.2B Samsung). In addition, RMBS offered incentives via warrents to DRAM manufactures.
"The biggest disappointment in 99 was Micron. If I was Intel, I would take a big baseball bat into Micron and demand to
know what my $500M bought. Intel should have spread the $500M around." - Tony Soprano. |
