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Sakkura

Skylake & Haswell-E PCIe lane misconception

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Posted · Original PosterOP

 As for Z97, can't seem to find a board that actually pulls pcie 3.0 x4 lanes from the cpu

 

Asrock Z97 Extreme6. Note the specs:

 

 

- 2 x PCI Express 3.0 x16 Slots (PCIE2/PCIE4: single at x16 (PCIE2); dual at x8 (PCIE2) / x8 (PCIE4))

 

*If M2_1 slot is occupied, PCIE2 slot will run at x8 mode, and PCIE4 slot will run at x4 mode.

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X99 getting lanes from cpu, that I already know, and yes Intel 750 is a gen 3 x4 device, was just saying X99 can do x4 mode, but forgot to mention it's only at 2.0 not 3.0. With the X99, not all boards are created equal, for some when a M.2 is installed then one of the x16 slots will get disabled, while others will actually let you allocated the a set of PCIe lanes between the x16 slot and M.2 in the bios. As for Z97, can't seem to find a board that actually pulls pcie 3.0 x4 lanes from the cpu, all I see are dual at x8 pcie 3.0, with 3rd slot running at 2.0 x4, but that 3rd slot is shared with SATA Express which pulls its lanes from the z97 chipset. Anyway when there are not enough PCIe lanes go around for all of your pcie devices, the board will either not let you use it, or reduce the performance of it by cutting down the number or PCIe lanes.

Spot on. Almost.

It's a little more complex. As it stands a CPU, let's say 4 core, will crunch data, then send a command down a SATA "lane". It'll then send this data using one core, down one lane. Hence the slow speeds. M2 was designed to overcome this. Chipsets first used DMI 2, z97 across 2 pcie lanes, good 2 cores can now send data, allowing I guess 6GBp/s, then the x99, allowing 10 GBp/s across 4 lanes - great - all 4 cores can be utilised.

Thus

An X99 with an M2 (pcie3 - 4 lanes) will only deliver 10 GBp/s because it's limited to DMI 2.0

The Z170, with an M2 (pcie 3 - 4 lanes) will be able to deliver 32 GBp/s because of DMI 3.0

You do the math. Data Media Interface (seems to effect speed a crap load).

All boards, using chipset pcie lanes share these with multiple others, usually sata express etc... The Asus Deluxe looses 2 sata express ports for the M2. This is the nature of a chipset, it "channels" data to multiple areas of the board ie. USB, SATA etc... And no, you can't have all those lanes open at once, imagine the streets with no stop lights. But it's the direct PCIe lanes to the CPU & DMI version that effect data speed. All else is the arena of GPU's as we can see they bypass the DMI and go directly to the CPU

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Spot on. Almost.

It's a little more complex. As it stands a CPU, let's say 4 core, will crunch data, then send a command down a SATA "lane". It'll then send this data using one core, down one lane. Hence the slow speeds. M2 was designed to overcome this. Chipsets first used DMI 2, z97 across 2 pcie lanes, good 2 cores can now send data, allowing I guess 6GBp/s, then the x99, allowing 10 GBp/s across 4 lanes - great - all 4 cores can be utilised.

Thus

An X99 with an M2 (pcie3 - 4 lanes) will only deliver 10 GBp/s because it's limited to DMI 2.0

The Z170, with an M2 (pcie 3 - 4 lanes) will be able to deliver 32 GBp/s because of DMI 3.0

You do the math. Data Media Interface (seems to effect speed a crap load).

All boards, using chipset pcie lanes share these with multiple others, usually sata express etc... The Asus Deluxe looses 2 sata express ports for the M2. This is the nature of a chipset, it "channels" data to multiple areas of the board ie. USB, SATA etc... And no, you can't have all those lanes open at once, imagine the streets with no stop lights. But it's the direct PCIe lanes to the CPU & DMI version that effect data speed. All else is the arena of GPU's as we can see they bypass the DMI and go directly to the CPU

 

M.2 on the X99 is handled by the cpu not by the X99 chipset, so it's still runs at PCIe 3.0 not 2.0. The X99 chipset just handles the SATA Express, usb3, ethernet, and other devices where pcie 3.0 isn't really needed.

Socket 1151 cpu only has 16 lanes so the rest of the work is handled by the  Z170 chipset, on the X99 there is 28/40 lanes so the cpu handles most of it.


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M.2 on the X99 is handled by the cpu not by the X99 chipset, so it's still runs at PCIe 3.0 not 2.0. The X99 chipset just handles the SATA Express, usb3, ethernet, and other devices where pcie 3.0 isn't really needed.

Socket 1151 cpu only has 16 lanes so the rest of the work is handled by the  Z170 chipset, on the X99 there is 28/40 lanes so the cpu handles most of it.

Your right. You might have misread. Yes. The X99 has a PCI lane to the CPU.

But both the z170 & x99 have the same pci 4 lanes to the CPU and both use the chipset (PCH) to communicate to the CPU.

Are you saying the M2 on an x99 bypasses the Platform Controller Hub on the chipset & communicates directly to the CPU? Sorry, do a little digging... Chips crunch data, they definitely do not send data directly to any storage device.

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Your right. You might have misread. Yes. The X99 has a PCI lane to the CPU.

But both the z170 & x99 have the same pci 4 lanes to the CPU and both use the chipset (PCH) to communicate to the CPU.

Are you saying the M2 on an x99 bypasses the Platform Controller Hub on the chipset & communicates directly to the CPU? Sorry, do a little digging... Chips crunch data, they definitely do not send data directly to any storage device.

I'm saying m.2 in x99 runs at gen 3 x4 so it produces the same bandwidth of 32gb/s.


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M.2 on the X99 is handled by the cpu not by the X99 chipset, so it's still runs at PCIe 3.0 not 2.0. The X99 chipset just handles the SATA Express, usb3, ethernet, and other devices where pcie 3.0 isn't really needed.

Socket 1151 cpu only has 16 lanes so the rest of the work is handled by the  Z170 chipset, on the X99 there is 28/40 lanes so the cpu handles most of it.

This is correct!

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Here am I with my Z77 biostar board and 3570K and I don't even have an SSD..

But yeah the 5820K is theoretically still better.


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Here am I with my Z77 biostar board and 3570K and I don't even have an SSD..

But yeah the 5820K is theoretically still better.

I couldnt deal with a Biostar board...

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In the UK, there's a problem with that.

 

Both CPUs are basically the same price, so you'd be looking at motherboards more than anything, and they can be pricey on the X99 platform.

Really, the motherboard is the only factor that is going to affect how much you dish out for your system. Though, I do still intend to acquire the X99 platform since it calls out to me. Do I need it? Heck no. Do I WANT it? Absolutely!

frys had a sale this weekend for the 4970 and 5820 for a 30 dollar difference.

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I couldnt deal with a Biostar board...

4 years and counting. Actually don't have any problems lol

 

guess sometimes you get lucky. Still wasn't a smart buy though, but I didn't know anything when I bought it so ¯\_(ツ)_/¯


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Was thinking about skylake-e and realized its 6 channel ram will look ridiculous.


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Bradwell-E may not even exist with how the other non mobile parts have been.

 

Already been roadmapped, dude. The likelihood of Broadwell-E not happening is very slim.


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Was thinking about skylake-e and realized its 6 channel ram will look ridiculous.

Im imagining the other 4 slots being above or below the socket.

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Im imagining the other 4 slots being above or below the socket.

I imagine it will look just like the current x99 but with 2 more slots on each side. But then there will be no room for the vrms, mosfets, chokes, etc. So the board will have to be E-ATX, unless they put the ram slots on all 4 sides of the socket.

What skylake-E board may look like, with 6 ram slots on each side?

xlz0nb.jpg


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No had a X99 and have a Z170 my Samsung M.2 perform identical. Even better I have 2 M.2 sockets and have close to double my read/write speeds of the M.2 so there is no bottle neck through the controller. Only way I can see is he have additional input/out and 3 or 4 SSD drives to the controller and they all go off at the same time.

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Okay so I am not completely clear on the whole PCIe lanes still. Here is my envisaged setup and usage summary:


  1. I will never run SLI or Crossfire.
  2. Not interested in M2 solid state drives.
  3. Never really bother or will ever bother with overclocking.
  4. Ordered a 980Ti as part of my upgrade from a socket 1156 (P55 Express chipset) upgrade.
  5. Have no need for extra LAN ports, sound card, PCIe ports beyond for the GPU, etc.

To this end I have choosen the ASUS B150M-K paired with the Intel i5-6400. From all the Intel tech papers and wiki I cannot make out if there is a performance issue between Z179 and B150. Both have DMI 3, System Bus speed of 8 GT/s, PCI Express 3.0. So for my usage scenario I do not see the point of splashing out for a Z170 with all sorts of bells and whistle which does not impact performance directly even running DDR3 versus DDR4.


 


The only thing I am unclear of is that B150 supports a maximum of 8 PCI Express lanes and the Z170 supports a maximum of 20 PCI Express lanes. The CPU (i5-6400) supports 16 maximum PCI Express lanes.


 


How does the CPU and motherboard PCI Express lanes play of each other?


 


The motherboard manual of the ASUS B150M-K does not indicate weather the PCI Express x16 port is shared with another PCI Express port, USB, SATA, etc. So if the chipset supports a max of 8 PCI Express lanes does it mean that the advertised PCI Express x16 lane on the ASUS B150M-K board actually can only run at x8?


 


Informational links to my post:


 


Comparison of all the chipsets and CPU mentioned above: http://ark.intel.com...185,90592,90591


ASUS B150M-K motherboard information: https://www.asus.com...specifications/


Online retailer price for the ASUS B150M-K motherboard: http://nam-webshop.c...m?item_id=14939 (displayed currency is Namibia Dollar)


B150 block diagram: http://www.intel.com...50-chipset.html


Z170 block diagram: http://www.intel.com...et-diagram.html


Wikipedia chipset info: https://en.wikipedia...ipsets#LGA_1151


                                  https://en.wikipedia.org/wiki/LGA_1151

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Asrock Z97 Extreme6. Note the specs:

 

 
Do I need to buy Asrock Z97 Extreme if I dont want use  M.2 PCI express x4 SSD adaptor card ??
I want buy Samsung 950 PRO 512GB M.2 SSD  and  I dont want use  M.2 PCI express x4 SSD adaptor card
Will me gtx 780 have reduced speed x8 if I install  950 PRO  in M2 slot?
Because when I have  installed  Intel 750 Series NVMe PCIe SSD/Solid State Drive 400GB .. gtx 780 was x8 speed on asus Z97 deluxe motherboard.
Me current system is  ASUS deluxe Z97 and i7 4770K

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Posted · Original PosterOP

@1-0-1 the CPU and chipset each provide their PCIe lanes separately. The motherboard you're looking at gives all the 16 PCIe 3.0 lanes from the CPU exclusively to the main PCIe slot, where you'll plug in your graphics card. All other slots and ports run off the chipset.

 

@jaaa1976 I'm sure there are other Z97 boards with the capability. But since the Z97 chipset doesn't have the lanes available, the board has to take those lanes from the graphics card, so it ends up running at x8.

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@jaaa1976 I'm sure there are other Z97 boards with the capability. But since the Z97 chipset doesn't have the lanes available, the board has to take those lanes from the graphics card, so it ends up running at x8.

So if  I want use 2  Samsung 950 PRO 512GB M.2 SSD...  1 for boot (OS) and second  Samsung 950 PRO 512GB M.2 SSD for storage ,,only  options is go to  Z170 ??

and if..I will need to buy new cpu,ram and motherboard ?


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Posted · Original PosterOP

So if  I want use 2  Samsung 950 PRO 512GB M.2 SSD...  1 for boot (OS) and second  Samsung 950 PRO 512GB M.2 SSD for storage ,,only  options is go to  Z170 ??

and if..I will need to buy new cpu,ram and motherboard ?

 

At least if you want both 950 Pros to run at full speed, yes. And that would indeed mean replacing both the CPU and motherboard, and maybe the RAM depending on whether the board would support your old DDR3.

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In the UK, there's a problem with that.

 

Both CPUs are basically the same price, so you'd be looking at motherboards more than anything, and they can be pricey on the X99 platform.

Really, the motherboard is the only factor that is going to affect how much you dish out for your system. Though, I do still intend to acquire the X99 platform since it calls out to me. Do I need it? Heck no. Do I WANT it? Absolutely!

I knopw this feel i just got £5k out of no where just blow it all on buildign an x99 rig and 12 months server rental haha

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At least if you want both 950 Pros to run at full speed, yes. And that would indeed mean replacing both the CPU and motherboard, and maybe the RAM depending on whether the board would support your old DDR3.

X99 does it without issue, you just need to use add-in cards (and a non-stupid motherboard). Like the x99 sli plus even has this ability.

1 add in card for good mobos and 2 for dumb ones.


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Posted · Original PosterOP

X99 does it without issue, you just need to use add-in cards (and a non-stupid motherboard). Like the x99 sli plus even has this ability.

1 add in card for good mobos and 2 for dumb ones.

 

Then it's technically not the motherboard doing it. Also, add-in cards add cost and complexity. It's more of a workaround than a solution IMO. But at least you have the option.

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