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Question Why are we not seeing edram on CPUs?

ChiefBigFeather

Junior Member
Jul 15, 2018
18
2
41
Dear Community,

ever since the invention of the 5770c with edram L4 cache, I have been curious about the topic. The 5770c was very fast in some gaming applications, presumably those with lots of cache misses. There has been talk about edram in various CPUs since then, the ones I remember were Skylake and Zen 3. Since the latest leak, edram on Zen 3 seems pretty unlikely.

This leads to my question: Why is no one making a desktop CPU with edram L4? Is it too expensive to produce? Is the latency not good enough? Is the market for such a product too small?
There must be some reason for this. My best guess is, that AMD is focused on the server marked and Zen is mostly a by product. High end gaming CPUs are probably such a small market, developing this may not be feasible. But maybe you got a better technical explaination for this.

Thanks in advance for input on that matter!
 

DaaQ

Member
Dec 8, 2018
75
34
51
Dear Community,

ever since the invention of the 5770c with edram L4 cache, I have been curious about the topic. The 5770c was very fast in some gaming applications, presumably those with lots of cache misses. There has been talk about edram in various CPUs since then, the ones I remember were Skylake and Zen 3. Since the latest leak, edram on Zen 3 seems pretty unlikely.

This leads to my question: Why is no one making a desktop CPU with edram L4? Is it too expensive to produce? Is the latency not good enough? Is the market for such a product too small?
There must be some reason for this. My best guess is, that AMD is focused on the server marked and Zen is mostly a by product. High end gaming CPUs are probably such a small market, developing this may not be feasible. But maybe you got a better technical explaination for this.

Thanks in advance for input on that matter!
I think it has to do with cost per mm2 on the die. Someone more knowledgeable should chime in though.
 

turtile

Senior member
Aug 19, 2014
441
41
91
Just guessing that it's not worth the cost of both developing and producing.

It looks like the future will be HBM chip on package.
 

gdansk

Senior member
Feb 8, 2011
404
68
91
It needs an embedded refresher and most CPU workloads benefit more from a larger L2 or L3 than a eDRAM LLC. It's more useful in cases where you have a GPU.
 

NTMBK

Diamond Member
Nov 14, 2011
8,455
1,293
126
There were rumours that Intel was preparing an i9-9900KFC- K = unlocked, F = no GPU, C = eDRAM cache. Doesn't look like it's happening though, which is a shame.
 

NostaSeronx

Platinum Member
Sep 18, 2011
2,650
408
126
i7-8559U is in a NUC, that is sort of a desktop thing. It has 128 MB of eDRAM/L4. It has a refresh successor with the i7-8569U.

2019 IEDM can have a hint for the future:
"STT-MRAMs for L4 Cache: Intel researchers will present a step forward for STT-MRAM technology, in a paper that details array-level MTJ process, performance and reliability requirements for the use of STT-MRAMs in L4 cache operations. They built 2MB arrays of scaled MTJ devices capable of meeting L4 cache specifications across all operating temperatures. The chips demonstrated a 20ns write time, 4ns read time, endurance of 10^12 cycles, and memory retention of one second at elevated temperature (110ºC). Bit error rates were low enough that they could be detected and corrected with error-correcting code (ECC) techniques."

From Toshiba:
"VoCSM with practically unlimited endurance even with a 5 ns-write time has been reported. Also, VoCSM read time operation using VCMA-MTJ is reported to be 10 to 20 ns for high-density embedded memory."

sttmram.png

eSRAM, eDRAM, eMRAM are all embedded on a single die vs 2.5D HBM. If you find it, it is for deep-learning... with DL Boost being present in Icelake-client it sets future L4 being MRAM-based to very likely.

Generally speaking the OPIO(On-package I/O) and its successor(Multi-die fabric interface?) is still lower power than HBM is currently.
 
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ZGR

Golden Member
Oct 26, 2012
1,830
250
126
There were rumours that Intel was preparing an i9-9900KFC- K = unlocked, F = no GPU, C = eDRAM cache. Doesn't look like it's happening though, which is a shame.
This was my planned upgrade. I wanted my next CPU to have an L4 cache as well. But I did assume it would have a fast iGPU as well. I really like having a strong backup iGPU. It has saved me a few times already.

When I first heard about the 5775C, I thought Intel would have continued it on the desktop. It makes sense that they didn't in hindsight.

i7-8559U is in a NUC, that is sort of a desktop thing. It has 128 MB of eDRAM/L4. It has a refresh successor with the i7-8569U.
I wanted to see some older Skull Canyon comparisons of Broadwell-C, but it is hard to compare. At stock, these CPU's throttle like crazy under heavy load. Only Broadwell-C on a Z motherboard has the ability to be unlocked. Sadly, Broadwell was a bad overclocker and was limited to 2400 DDR3. So one had to get the lowest latency DDR3 they could find.
 

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