Enable OPI GT4 on Skylake U System for FULL nVme speed

The Latitude is designed for stability and reliability - meaning that the extra margin  gained by under-speed of the SSD goes directly toward that.

It's as simple as a design decision made for the system's market purpose.  This is not a performance notebook - it's a business tool.

That's not true since the 5480 with HQ processor works at 4x.

I understand that the "HQ" chips use a DMI link which is not the same as the OPI with "U" chips. Nevertheless, I would like to know the technical reason behind that because (correct me if I'm wrong) it seems that it's designed to works at 4x.

For instance the Apple MacBook Pro 13 without touchbar is also equipped with a 14w "U" chips and has read sequential transfer rate above 2000 mo/s while I'm stuck at 1750 mo/s with my 5470 and Samsung 960evo.

Of course it's not an absolutely necessary feature, but if it's designed to works with 4x why not do it ??

And actually, are you even sure the 5480 uses GT4?  Number of PCIe lanes is NOT the same thing as OPI mode, even though both can obviously affect performance.  The XPS 13 has a x4 M.2 slot but operates at GT2, so when you say the 5480 "works at 4x", that doesn't necessarily mean it runs at GT4 speed.  Not that it really matters for your case, though.

This came up in another thread recently because the XPS 13 also uses GT2 rather than GT4, whereas the XPS 15 uses GT4.  I doubt you're going to get a technical answer from a Dell engineer here, but possible explanations are that Dell determined that GT4 makes a significant difference in battery life even when not under load and was aware that their target market with these systems was more interested in battery life than faster SSD performance.  And if they had made this option configurable in the BIOS, testers might have only tested with GT4 and published battery life results based on that configuration, and battery life is a spec cross-shopped far more commonly than SSD transfer rate.  Also consider that the Samsung 960 Evo's performance makes it a "Class 50" SSD according to Dell's internal designations, and Dell only sells Class 50 SSDs as options in Precision models; the SSDs available in Latitudes are Class 20 (SATA M.2) and Class 40 (NVMe, but not absolute top of the line), so the SSDs available from the factory wouldn't even be bottlenecked by GT2, in which case from Dell's perspective, they're getting extra battery life with no performance downside.

And another possibility is that there were thermal concerns about running Class 50 SSDs in GT4 mode in that particular system.  Maybe the 5480 has an improved cooling design.  That would certainly explain the difference between the XPS 13 and XPS 15 given that both of those ARE billed as performance and semi-gaming systems, so you would expect both of them to be set up for max performance unless there were some other concern -- but the XPS 13's cooling isn't nearly as robust because it's smaller and doesn't even have a discrete GPU option.  Also, the XPS 15 has a sister system the Precision 5520, where Class 50 SSDs are an option from the factory.

As you can see here => en.community.dell.com/.../19992358

Only the 5480 with "HQ" chip is at 4x speed. But it's not relevant in this case since "HQ" chips use DMI bus, not OPI. I decided to speak about the 5480 to show @ejn63 that latitude laptop can perfectly handle this kind of spec.

While in the same topic it is also state that the 5470 with "U" chips operate at 2x. So I believe that the 5480 has GT4.

Now, talking about power consumption, if you look at the Anandtech article ( www.anandtech.com/.../5 ), it clearly show that there is no difference between GT2 and GT4 with a class 50 SSD regarding the power consumption. Actually the difference between GT2 and GT4 is about 0.3 watt ...