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Technology Stocks : Rambus (RMBS) - Eagle or Penguin
RMBS 92.35-0.4%Nov 25 3:59 PM EST
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To: jim kelley who wrote (41966)5/10/2000 9:25:00 PM
From: Bilow  Read Replies (1) of 93625
 
Hi jim kelley; What you are attempting to calculate is the power consumption of dual 128MB RIMM system versus the power consumption of a dual 128MB DDR DIMM system. You are getting confused with all the various current values and power consumption modes. Here is the simple technique.

Go to the Samsung website and find the pdf file describing the 128MB RDRAM RIMM module. In fact, I'll do it for you. Here it is:
usa.samsungsemi.com

Now run your finger down to page 12. There is a diagram showing the label. Look at item G: Note the international symbol indicating burning fingers. That should be enough for you, leave the arithmetic to the engineers.

So you want to see the actual MAX power consumption figures? Go to page 7. There you will find a table of Idd values for various combinations of mode and memory size. Under the column for 128/144MB, look down at the combination of Idd3 and 128MB for the -800 part. You get 1650mA, and that is the number you want. Any other mode is going to further compromise RDRAMs already poor latency figures as compared to DDR.

Carefully take note of "Note (a) Power consumption does not include refresh current." Because of this note, we will also ignore refresh current on the DDR device. In actual use, these currents are small compared to the operating current of the devices, given the small percentage of the time that the parts are being refreshed, and the average refresh currents of the devices are presumably going to be similar (though I haven't checked, it really just doesn't matter much).

Now look up the corresponding DDR figures.

Samsung's DDR DIMM power consumption is still "TBD"
( usa.samsungsemi.com )

so go to the Micron website. Look on page 15 of this link:
micron.com

On that page there is a table of current consumption. Since we are comparing PC800 (with bandwidth 1.6GB/sec per RIMM) to PC200 (also with 1.6GB/sec per DIMM), look under the "-202" column. Note Idd4W for 128MB devices: 1400mA.

Note that DDR DIMM's current consumption is somewhat less than the RDRAM RIMM.

Also note no burning finger warning. This is because most of the power isn't going to be dissipated by just a single device. DDR is simpler to engineer because of this already spread power consumption. This means that DDR saves a significant cost per DIMM, as it doesn't need a heat spreader.

-- Carl

P.S. If you want to redo the calculation with half your RDRAMs in NAP mode, then you should be comparing your stick of RDRAM to a stick of DDR DIMM built with 8Mx16 DDR chips, not the 16Mx8 types. This will then allow half the DDR parts to also be put into a power down condition. But that is another calculation.
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