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Author Topic: MAG Z390 TOMAHAWK M.2 & SATA combination  (Read 371 times)

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melanie.birdwordTopic starter

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MAG Z390 TOMAHAWK M.2 & SATA combination
« on: 11-January-19, 07:29:01 »


is the M.2 & SATA combination table in the manual correct?

I am refering to 7B18v1.0(G52-7B181X1)(MAG Z390 TOMAHAWK).pdf, page 29.

a) It is unusual that populating M2_2 with SATA blocks not only one but two connectors (SATA5 and 6).
b) It is unusal that populating M2_2 with PCIe also blocks these two connectors.

Is the the table correct?
Where does the limitation come from?



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Re: MAG Z390 TOMAHAWK M.2 & SATA combination
« Reply #1 on: 11-January-19, 13:05:09 »

Yes the manual is correct. The Intel Z390 (and Z370) chipset has got only 24x PCIe 3.0 (PCH) lanes. These 24 lanes are unfortunately not enough to allow the six SATA ports, two M.2 slots and four PCI Expansion slots all to be populated at the same time. So some of the SATA ports are disabled when both the M.2 slots are populated.
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melanie.birdwordTopic starter

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Re: MAG Z390 TOMAHAWK M.2 & SATA combination
« Reply #2 on: 11-January-19, 17:49:45 »

Thanks for trying to explain. Sure there is some sharing needed. Regarding PCIe it gets complicated because there are also the PCIe slots involved and some lanes are coming from the CPU directly. But after all, in my opinion PCIe has nothing to do with the SATA lanes. I don't expect PCIe to influence the SATA connectors.

The Z390 chipset supports a maximum of 6 SATA ports. So there must be a Sharing between M.2 and SATA. If an M.2 gets populated, a SATA connector is disabled.

To clarify: What I expect is something like attached.
See also the Z390 motherboard block diagram.



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Re: MAG Z390 TOMAHAWK M.2 & SATA combination
« Reply #3 on: 11-January-19, 19:34:21 »

Actually.....Z370 and Z390 technically have 30 PCIe lanes....however 6 of them are taken up by reserved resources. That's why you have 24 available PCIe lanes.
Then, those are split up for resources.

Take a look at this : HSIO Lanes

That isn't exactly how the MSI boards are done I don't believe, but it gives you an idea.

Most likely though, I would wager that the diagram is wrong. (MSI does get them wrong from time to time).
But without that board, I can't say if it's right or wrong.
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melanie.birdwordTopic starter

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Re: MAG Z390 TOMAHAWK M.2 & SATA combination
« Reply #4 on: 12-January-19, 21:16:57 »

Ok - thanks, I think I got the idea. Not sure about it, though, since I didn't spent much time to dig into it.
As usual nowadays chips do have way more features than they are able to map on the available pins. A rich feature set and low pin count (low package cost) is a selling proposition.
HSIO seems to be general Gbit transceivers. These transceivers can drive PCIe, SATA, USB, ... lanes. They are connected through multiplexers to the respective controllers.
Thus, there is a sharing of resources between different protocols. This may be the reason for the unexpected combinations in the table.

I also asked the MSI support, got a very short answer without a word of explanation:
"Regarding your concern, sorry to say that the manual is right according to the MB specification."

And yes, I also saw some flaws in the MSI docs. For example in the block diagram of the Tomahawk. The PCIe connection to M.2 is missing (started at the PCH but not finished?). The block diagram is odd at the same point where the combination table is odd...
I think, I will give Asus a try. Sharing is as expected. And the documentation and the BIOS seems to be more reliable.

Thanks for disussing this topic with me!
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