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Paul A. Clayton
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Paul A. Clayton   7/4/2014 10:35:10 AM
Embedded DRAM (I prefer eDRAM as an abbreviation since EDRAM was previously used for Enhanced DRAM) has significant density advantages, but involves significant addition manufacturing cost. This is somewhat like incorporating flash memory into a computation-oriented chip—it adds cost and may have delayed availability or delay the roll out of a new process—, but incorporating flash can more easily reduce system cost for small systems by removing the need for external persistent storage.

If an eDRAM-capable process is available sufficiently later at sufficiently higher cost, it can be attractive to use a smaller ordinary process and use SRAM since the smaller process will shrink and increase performance/energy-efficiency of the logic and make SRAM density more comparable to eDRAM in the older process.

eDRAM is most useful when bandwidth or latency demands integration but the desired capacity would be too great for practical integration if SRAM was used. (eDRAM also has some error resiliance advantage over SRAM.) This makes it great for huge L3 caches integrated into the processor chip (or even just in the same multichip module as the processor chip). It could also be useful as a high bandwidth memory for a GPU.

The lack of great success of Mosys' 1T SRAM (higher performance DRAM abstracted behind an SRAM interface) hints that the market for a memory with its capacity advantage is not especially large. (I seem to recall it was used by HP for a PA-RISC processor's off-chip cache.)

For a foundry eDRAM seems to be something of a niche feature (more so than support for integrated flash memory). Without IBM's server demand for such, the market may not be able to support the extra costs. Process development is already expensive and risky, so Global Foundry's rejecting the extra cost and risk for such a niche feature is understandable.

(I also seem to recall that IBM's eDRAM techology was linked with SOI. SOI also adds cost and seems to be less popular among foundry users.)

A technology can be theoretically very useful ("great") without being very profitable.

By the way, IBM's POWER7 exploited the presence of trench capacitors to provide better power regulation. This additional advantage might expand the niche slightly but only slightly.

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alex_m1   7/4/2014 7:19:29 AM
If EDRAM is so good, and IBM is talking about selling it to someone, doesn't it give IBM levearge to ask for specific conditions , for example an ability to purchase wafers using EDRAM at a reasonable price ?

And if that's the case, it's most likely a secret from us and company employees ,as common in negotioatios.

And if the tech is so great , why wouldn't global foundries use it ?

rick merritt
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Other views?
rick merritt   7/4/2014 4:41:45 AM
I hope this employee's candor inspires others to speak frankly.

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What a pity
Violoncelles   7/4/2014 2:30:13 AM
I 'm also probably biased as well as a former IBM microelectronics employee who worked at IBM Essex Junction , East Fishkill and Corbeil-Essonnes(France) plants.

I found at these locations (at least the 1st two) extremely good expert people.

May-be the manufacturing people is not the best of breed.

I had also the luck to work on eDRAM and this is a fantastic technology.
I found it a pity that this might disappear. But business is business.

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IBM and hardware
Sheetal.Pandey   7/4/2014 2:25:20 AM
IBM's name is seen synomynous with hardware business. Its hard to believe that IBM can be only software development company. There are numerous software companies already being there. IBM stands out from crowd because of their hardware experience.

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