Hi Charles R; Re your long/short term use of RDRAM &c...
I thought I'd comment on the high end graphics stuff, particularly with regard to eDRAM.
You said: I can see the appeal but I am unsure how this would compete with embedded DRAM In this I am sure you are correct.
Given a display size (in the future) of 2048x2048, with 8 bits per pixel, RGB, the total memory size is 96Mb. Embedded DRAM could certainly put that on a chip, in fact, IBM's standard cell data book gives 128Mb as an example.
For a smaller picture size, the memory requirement would decrease. You might want to offer two frames of data, this would double the memory requirement.
The average bandwidth requirement for such a display would be 96x60 Mb/sec, assuming a 60 Hz refresh. (Such slow refereshes hurt my eyes, but the resolution is kind of high, anyway.) This is a total bandwidth of 750MB/sec, call it 850MB/sec peak, where I assume a FIFO sufficient in size to buffer a line, but not, of course, a frame.
You also need to have some bandwidth to write to memory, and if you want to require that you can rewrite the whole memory in a single frame (1/60 of a second), then this about doubles the bandwidth requirement to 1600MB/sec.
This kind of memory bandwidth could almost be provided by a single RDRAM chip, while that single chip would easily provide sufficient capacity.
DDR SGRAM could provide that bandwidth only by going to two chips. The total system cost might end up being quite similar to RDRAM, due to lower DDR SGRAM chip costs, and other things like heat sink, termination, etc. I haven't looked at pricing for DDR SGRAM, but usually SGRAM is pretty cheap. The reason for this is that they don't put very many memory cells on a chip, relative to the other processes. So the chips are small, but have a lot of I/O. The I/O savings of RDRAM will not save much money due to the lowered cost of modern high pin count packages. For example, IBM's standard cell allows something like 1700 pins per package.
As for the future, the trend in memory capacity and bandwidth has been faster than the trend in display sizes. For example, a 1280x1024 screen has 16 times as much data as a 320x240 screen, but early DRAMs were about 256,000 times smaller than the current generation. Because of this remarkable disparity in long term growth rates, it is likely that embedded DRAM will hold the future for high end display controllers. That is, embedded DRAM will allow sufficient capacity at system prices that will be below system prices that use discrete DRAM.
In other words, system on a chip is the wave of the future.
-- Carl |
