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To: jim kelley who wrote (41966)	5/10/2000 5:36:00 PM
From: Bilow	Read Replies (2) \| Respond to of 93625

hi jim kelley; Re power consumption of DDR vs RDRAM... Here's a picture of a typical 333MHz GeForce2 graphics card. It has a 128-bit wide memory bus. It uses four x32 DDR SGRAM chips. This provides 5.3GByte/sec bandwidth, more than could be obtained from 3 Rambus chips at only a much higher cost. Since there is only one bank, all of these chips are used every time memory is accessed, so their power consumption is the maximum that a DDR system can achieve. (The power consumption is something like 300mA per chip, max, well under the amount that an RDRAM sucks.) Note that there is no heat spreader on these DDR memory chips. (They undoubtedly benefit from increased circulation due to the GPU fan.) This is in distinction to RDRAM solutions, which invariably have something metallic attached to the RDRAM chips in order to conduct heat away. Also note that the concentration of resistors near the memory chips is quite low, and extensive areas of PCB (in the upper right corner) have been left bereft of both passives and vias. This is obviously not a PCB that required a lot of layers to route. www7.tomshardware.com The same reasoning applies to DIMMs and RIMMs. The DIMMs are not equipped with heat spreaders, the RIMMs are. It really doesn't take a rocket scientist to figure out the consequences: (1) At the small memory end, individual DDR components require no special cooling, individual RDRAM components do. (2) With mid size memories, RIMMs requires heat spreaders, DDR DIMMs do not. (3) With high end server memories, RIMMs require heat spreaders, DDR DIMMs do not. Make as many errors in your power consumption calculations as you would like, the fact is that DDR designs are being shipped without special memory cooling techniques, while no RDRAM systems are shipping without RDRAM heat spreaders. -- Carl

To: jim kelley who wrote (41966)	5/10/2000 9:25:00 PM
From: Bilow	Read Replies (1) \| Respond to 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.