By: Someone with gray hair (, June 3, 2022 11:36 am
Room: Moderated Discussions
What do people here think of using 29 LPDDR5 DRAM packages to get 2.9 TBytes/sec of DRAM bandwidth for a GPU? The DRAM packages could be mounted on both the top and bottom of a module in a 3 x 5 array. The total number of signal connections to these DRAMs is 29 packages x 152 signals/package = 4408 signals. This seems doable since AMD’s Genoa is in a 6096 pin package. The area taken by the DRAM packages is about 4.8cm x 7.5cm, which is approximately 2 inches x 3 inches. Additional area would be needed for the connectors and on-module DC-to-DC converters.

For comparison, the Apple M1 Ultra has 800 GBytes/sec of DRAM bandwidth from 8 LPDDR5 DRAM packages with a minimum total memory size of 64 GBytes. Compared to HBM and GDDR DRAM, LPDDR DRAM has the advantage of being used in cell phones, which drives up sales and drives down prices.

I saw a similar situation when I worked at Silicon Graphics. Graphics frame buffers were implemented with a type of DRAM called VRAM. VRAM has two ports, one for updating the frame buffer and one for refreshing the display. VRAM provided about twice the bandwidth of regular DRAM. The price of regular DRAM fell much faster over time than VRAM. When VRAM was more than twice of the price of regular DRAM, it became more cost-effective to use twice as much regular DRAM to get twice the bandwidth instead of using VRAM. This provided twice the DRAM capacity at a lower price than VRAM.
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TopicPosted ByDate
GPU Using LPDDR5Someone with gray hair2022/06/03 11:36 AM
  GPU Using LPDDR5Someone with gray hair2022/06/03 12:27 PM
  How much power do you expect 29 DIMMs and 29 Memory Controllers to use?Mark Roulo2022/06/03 04:19 PM
    LPDDR5 DRAM is not in DIMMsSomeone with gray hair2022/06/03 07:08 PM
  Don't give Apple any ideas! (NT)Wes Felter2022/06/04 08:48 AM
    Don't give Apple any ideas!---2022/06/04 09:14 AM
    I'd be surprised if we see a discrete GPU from them [nt]me2022/06/04 02:15 PM
    Don't give Apple any ideas!Doug S2022/06/05 09:58 AM
  GPU Using LPDDR5Groo2022/06/05 04:26 AM
    GPU Using LPDDR5Someone with gray hair2022/06/05 12:04 PM
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