SD Express is a New Memory Card Standard That Leverages PCIe and NVMe

[suicidalfranco]

Kay, now give me a phone with it

[Zodiark1593]

2 hours ago, suicidalfranco said:

Kay, now give me a phone with it

Well, Apple already uses the NVME protocol with their iPhones, so technically, wish granted...

[Sniperfox47]

5 hours ago, Trixanity said:

That sounds extremely convoluted. Sounds like it adds tons of latency making NVMe useless.

 

I did hear future versions of PCI-E will focus on power in addition to bandwidth but it remains to be seen if anything comes to fruition.

 

Do you know if Apple made proprietary changes to PCI-E to make theirs work in phones?

It doesn't make it useless just less impactful. The actual SD protocol itself is hot garbage and always has been. It introduces a massive amount of overhead, latency and just generally terrible performance for anything less than the most linear and stable sequential writes. If you write in huge chunks your fine but random performance is trash because of the protocol itself.

 

Since these cards need to be backwards compatible with SD itself they can't just hotplug onto a PCIe lane, which would be incredibly convoluted by itself. PCIe doesn't like hotplugging because of resource allocation issues and other headaches. LTT actually did a video on it with a server motherboards a couple months back that gives a good idea fust how finicky it can be.

 

As far as changes for the iPhone I have no idea. I didn't think they actually had a full PCIe implimentation but was under the impression it was just a cut down one specifically for talking to the storage chip, but I may be wrong.

[suicidalfranco]

4 hours ago, Zodiark1593 said:

Well, Apple already uses the NVME protocol with their iPhones, so technically, wish granted...

talking about the sd card...

[Trixanity]

6 hours ago, Sniperfox47 said:

It doesn't make it useless just less impactful. The actual SD protocol itself is hot garbage and always has been. It introduces a massive amount of overhead, latency and just generally terrible performance for anything less than the most linear and stable sequential writes. If you write in huge chunks your fine but random performance is trash because of the protocol itself.

 

Since these cards need to be backwards compatible with SD itself they can't just hotplug onto a PCIe lane, which would be incredibly convoluted by itself. PCIe doesn't like hotplugging because of resource allocation issues and other headaches. LTT actually did a video on it with a server motherboards a couple months back that gives a good idea fust how finicky it can be.

 

As far as changes for the iPhone I have no idea. I didn't think they actually had a full PCIe implimentation but was under the impression it was just a cut down one specifically for talking to the storage chip, but I may be wrong.

Yeah, I know. When I said useless it was a bit hyperbolic. I mean not much could be worse than the SD protocol. The actual meaning was that you'd remove some if not many of the advantages of NVMe by adding latency and overhead by putting less performant interfaces between the host and the card.

 

It's difficult to switch away from ubiquitous legacy stuff but SD is so bad that we kinda need to move away from it and this does seem promising while maintaining some backwards compatibility (although scaling back to 100~ MB/s seq is a pretty steep price to pay for compatibility but I bet many if not all are willing to take it versus no compatibility). The risk with backwards compatibility is that it'll take a very long time to kill the old if not outright impossible. Perhaps they plan to phase out the compatibility if the Express spec takes off in a big way and fast.

 

I'm sure (if they did not pull any shenanigans) that the PCIe is very limited. They wouldn't want power to run rampant by beefing up the physical interface beyond what's necessary. I'm betting it's the classical engineering case of just making it barely work. But either way they've made it work somehow and the how would be interesting to know. It should be noted that I've heard some storage vendors making PCIe (and I assume NVMe) BGA packages for phones as well but of course we haven't seen any implementations yet and I'm not sure of how such a product would stack up against the latest UFS.

[Sniperfox47]

2 hours ago, Trixanity said:

I'm sure (if they did not pull any shenanigans) that the PCIe is very limited. They wouldn't want power to run rampant by beefing up the physical interface beyond what's necessary. I'm betting it's the classical engineering case of just making it barely work. But either way they've made it work somehow and the how would be interesting to know. 

I haven't read the spec but from everything I've heard it should be a fully standards compliant PCIe 3.0 link. The controllers will likely be cut down considering they can assume some constraints with only having to deal with NVMe (see realtek and ASMedia's new NVMe specific controllers/repeaters/converters).

 

It is only a 1x link to be clear so it's not anything crazy.

 

2 hours ago, Trixanity said:

It should be noted that I've heard some storage vendors making PCIe (and I assume NVMe) BGA packages for phones as well but of course we haven't seen any implementations yet and I'm not sure of how such a product would stack up against the latest UFS.

Yeah expect to see more ARM SoCs with PCIe as the laptop market for them expands. The Tegra chips have PCIe on them as well.

 

As far as comparing UFS to PCIe, a 2 lane UFS 3.0 connection (2900MB/s) is comparable to about 3ish lanes of PCIe (a little more than halfway between 2 and 4 lanes). Similar latency characteristics to NVMe, although NVMe has some useful features over the top like how it uses memory, and stuff like that.

 

As far as comparing UFS Card to SD Express, UFS Card is about 2/3 the speed of this over UFS 2.1 (600MB/s) and about one and a half times the speed of this over UFS 3.0 (1200MB/s) and can be wired directly to a UFS host, since UFS is hotpluggable meaning no weird middleman controllers.

 

[Doobeedoo]

That's really awesome. Seeing these small things improve so much.

 

Also I wonder about Samsung UFS SD cards.