By: Doug S (foo.delete@this.bar.bar), February 17, 2013 12:24 pm
Room: Moderated Discussions
David Kanter (dkanter.delete@this.realworldtech.com) on February 16, 2013 3:16 pm wrote:
> This is certainly one way to do it. The challenge is that those buffers take power,
> which is supposed to be the big advantage of an ARM SoC. I'd wager that using fully
> buffered memory would eat up any potential power gains and possibly reverse them.
>
> IIRC, buffers take something like 2W...which is a very large percentage of the power of an A15 core.
There is certainly a profitable market segment for servers with large amounts of memory, but much of it is for servers with high RAS requirements or high single thread performance. There isn't much point for ARM SoCs to play there, because any power or cost advantages would be lost in the noise versus the power and cost of the DRAM.
But you will still get some pretty decent capacities in reasonable ARM SoC configs. Today you can buy 8GB DDR3 DIMMs extremely cheap. In two years DDR4 will have doubled the number of ranks and 8Gb DRAMs will be in production, so 32GB DDR4 unregistered DIMMs will be available. At first at a premium price, but quickly becoming cheap as everything else once the 8Gb DRAMs ramp up.
ARM SoCs could probably be offered with as many as four memory channels before the pin counts get too crazy (that would be over 1100 pins just for the four channels) That's 128GB of dirt cheap RAM, which would cover a pretty decent swath of workloads.
> This is certainly one way to do it. The challenge is that those buffers take power,
> which is supposed to be the big advantage of an ARM SoC. I'd wager that using fully
> buffered memory would eat up any potential power gains and possibly reverse them.
>
> IIRC, buffers take something like 2W...which is a very large percentage of the power of an A15 core.
There is certainly a profitable market segment for servers with large amounts of memory, but much of it is for servers with high RAS requirements or high single thread performance. There isn't much point for ARM SoCs to play there, because any power or cost advantages would be lost in the noise versus the power and cost of the DRAM.
But you will still get some pretty decent capacities in reasonable ARM SoC configs. Today you can buy 8GB DDR3 DIMMs extremely cheap. In two years DDR4 will have doubled the number of ranks and 8Gb DRAMs will be in production, so 32GB DDR4 unregistered DIMMs will be available. At first at a premium price, but quickly becoming cheap as everything else once the 8Gb DRAMs ramp up.
ARM SoCs could probably be offered with as many as four memory channels before the pin counts get too crazy (that would be over 1100 pins just for the four channels) That's 128GB of dirt cheap RAM, which would cover a pretty decent swath of workloads.
