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Even a laptop can run RAM externally thanks to CXL

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Re: Even a laptop can run RAM externally thanks to CXL

#31

Post by cmrdporcupine »

gostsamo wrote: post #23
hadlock wrote: post #9

This wasn't mentioned in the article but CXL Stands for Compute Express Link which is an open standard, CPU-to-Device Interconnect, I guess they're on v3.0 now. First I had heard of it as well. 3.9GB/s on the low end and as high as 121.0GB/s with the latest 16x 3.0 spec over serial connection https://www.computeexpresslink.org/about-cxl https://en.wikipedia.org/wiki/Compute_Express_Link

I'm surprised that it is not known on HN. This is standard developed to enable different server configurations in the data center from what I've read through the years. The universal interconnect allows for adding and removing devices without special allowances for each device type as far as I get it. It might work for laptops, but it is not the main goal and it might be only Framework who will do something in that d…

These days that bulk of us people doing dev work aren't getting to play in the actual DC, it's all so abstracted away. Frankly looking to get a used rack or two at home here, just so I can play with the HW a bit.

(I do embedded and not server stuff mostly these days anyways, but generally interested in systems stuff, so)

Re: Even a laptop can run RAM externally thanks to CXL

#33

Post by dmw_ng »

It's been a long day, managed to take a few seconds wondering what this interesting new "best CPUs" technical architecture was before realizing the article is SEO'd blogspam.

Maybe switch to the source article? https://www.servethehome.com/fadu-cxl-2-0-switch-and-pcie-ge...

Re: Even a laptop can run RAM externally thanks to CXL

#34

Post by jnwatson »

e63f67dd-065b wrote: post #22

CXL is useful for many more things beyond just memory expansion (which is a "type 3 device"). The purpose of CXL is to allow for memory coherency between different CXL devices. To quote the spec on type 2 devices: > CXL Type 2 devices, in addition to fully coherent cache, also have memory, for example DDR, High-Bandwidth Memory (HBM), etc., attached to the device. These devices execute against memory, but their perfo…

CXL for CPU access to DRAM is overkill. Plenty of server mobos allow you to directly attach 2 TiB of DRAM.

Re: Even a laptop can run RAM externally thanks to CXL

#35

Post by lazide »

jnwatson wrote: post #34
e63f67dd-065b wrote: post #22

CXL is useful for many more things beyond just memory expansion (which is a "type 3 device"). The purpose of CXL is to allow for memory coherency between different CXL devices. To quote the spec on type 2 devices: > CXL Type 2 devices, in addition to fully coherent cache, also have memory, for example DDR, High-Bandwidth Memory (HBM), etc., attached to the device. These devices execute against memory, but their perfo…

CXL for CPU access to DRAM is overkill. Plenty of server mobos allow you to directly attach 2 TiB of DRAM.

Some 4 and supposedly 6TB now too.

Re: Even a laptop can run RAM externally thanks to CXL

#36

Post by gavinray »

e63f67dd-065b wrote: post #22

CXL is useful for many more things beyond just memory expansion (which is a "type 3 device"). The purpose of CXL is to allow for memory coherency between different CXL devices. To quote the spec on type 2 devices: > CXL Type 2 devices, in addition to fully coherent cache, also have memory, for example DDR, High-Bandwidth Memory (HBM), etc., attached to the device. These devices execute against memory, but their perfo…

CXL for Persistent Memory, as the Optane successor (or rather, sole-survivor if you will) is what excites me.

Persistent Memory databases are such a neat idea, it's a shame that the hardware for it isn't commonplace.

Re: Even a laptop can run RAM externally thanks to CXL

#37

Post by helf »

e63f67dd-065b wrote: post #22

CXL is useful for many more things beyond just memory expansion (which is a "type 3 device"). The purpose of CXL is to allow for memory coherency between different CXL devices. To quote the spec on type 2 devices: > CXL Type 2 devices, in addition to fully coherent cache, also have memory, for example DDR, High-Bandwidth Memory (HBM), etc., attached to the device. These devices execute against memory, but their perfo…

[dead]

Re: Even a laptop can run RAM externally thanks to CXL

#38

Post by wtallis »

xhrpost wrote: post #12

The slowest clock speed for DDR5 is 2,000Mhz or 0.5ns per cycle. At 2/3c, electricity should be able to travel about 10cm max in one cycle. I suppose 4Ghz RAM would be only 5cm. Is having an external unit with much greater than 10cm of copper travel ultimately a limiting factor here with modern day RAM speeds?

DRAM latency is tens of clock cycles. There's a minimum of about 10ns of latency happening within the DRAM chip itself, so a slightly longer bus doesn't affect total latency by much.
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