2Dex

Junior Member
Mar 1, 2019
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0
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Good evening everyone,

I hope I am posting on the right forum. If not please redirect me and I will be happy to correct my mistake.

I would like to understand more about PCIe lanes. And I would like to use my current (old) build as an example to see if my 48h of googl'ing has made me any wiser (or only more confused).
My secondary goal is to determine if I can improve my SSD read/write speed in my old build by upgrading f.e. to an NVMe PCIe based SSD or that I have to buy a new Motherboard and CPU as well.

My current build:

Motherboard: Asus P8Z68-V PRO (only PCIe 2.0 is supported, NOT PCIe3.0)
Chipset on MB: Intel Z68
CPU: i7 2700 K
GPU: Radeon RX 580


<< Sources >>
------------
Block diagram: https://www.overclock.net/photopost/...ckdiagram.jpeg
PCIe speeds: https://www.embedtek.net/wp-content/...18/12/char.png
Complete MB manual: https://dlcdnets.asus.com/pub/ASUS/m...8Z68-V_PRO.pdf

Question 1: Am I correct when I say that my CPU provides up to 16 PCIe 2.0 lanes (direct link from PCIe slot to CPU)? Either 1 slot at x16 speed or 2 slots at x8 speed each.

Question 2: My motherboard furthermore provides 4 PCIe 2.0 lanes (Not direct to CPU, but rather over the Z68 chipset) ?

Question 3a: Where does the 16Gbytes/s come from on the block diagram <<see link above>> on the x16 slot ? I thought PCIe 2.0 offers 500 MB/s per lane (= 8.0 Gbytes/s for x16) ?? <<see PCIe speeds link above>>

Question 3b: Same question as question 3a. If i assume the lower 'b' here in 5 Gb/s stand for bits (does the 'Gb' stand for Gbits/s and the GB for Gbytes/s ??), this would make sense since 5 Gbits/s = 625 Mbytes/s (500 Mbytes/s if I take the 8b/10b decoding into account). And 500 Mb/s is what I find to be the speed of PCIe 2.0 per lane in the << PCIe speeds link above >>.

Question 4: Does my motherboard support NVMe protocol ? OR only AHCI protocol ? (I assume it doesn't support NVMe since it is way old)

Question 5: I read a lot about the fact that PCIe slots can be connected to the CPU using PCIe lanes OR SATA III connection. It depends on the MB manufacterer. Is this true and how can I check this ? My MB manual doesn't specify it. EDIT: @Campy you are right. This question didn't make any sense. I meant to say that M.2 slots can be connected on the motherboard either with PCIe lanes or SATA III connection, but I understand now that that's also wrong ? An M.2 slot is always physically/electrically connected on the Motherboard with PCIe lanes (usually, but not always over the chipset) but can operate on these lanes with either the NVMe protocol (a.k.a. PCIe mode?) or the SATA III protocol (600MB/s SATA). Either protocol "is sent over/uses" the PCIe lanes.

I have some more questions, but I will hold them for later
tongue.gif

I hope I put enough structure in my post for you to understand my situation.
 

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Solution
1. Yes.

2. Yes.

3. Yes, it looks incorrect. Big B is Byte and small b is bit.

4. It would appear it does not support NVMe

5. This question doesn't make any sense, PCIe slots have nothing to do with SATA. PCIe slots are connected either directly to the CPU or through the chipset (and DMI link to the CPU).
Your motherboard has the two top x16 slots wired directly to the CPU and the bottom one to the chipset.
Some M.2 slots can operate in both NVMe mode and SATA3 mode, but that is manufacturer dependant. On Intel mainstream platforms the M.2 slots are routed through the chipset.

Campy

Senior member
Jun 25, 2010
785
171
116
1. Yes.

2. Yes.

3. Yes, it looks incorrect. Big B is Byte and small b is bit.

4. It would appear it does not support NVMe

5. This question doesn't make any sense, PCIe slots have nothing to do with SATA. PCIe slots are connected either directly to the CPU or through the chipset (and DMI link to the CPU).
Your motherboard has the two top x16 slots wired directly to the CPU and the bottom one to the chipset.
Some M.2 slots can operate in both NVMe mode and SATA3 mode, but that is manufacturer dependant. On Intel mainstream platforms the M.2 slots are routed through the chipset.
 
Solution

Midwayman

Diamond Member
Jan 28, 2000
5,723
325
126
4) Sort of. I had a nvme on a sandy bridge via an add in card. The issue is that it can't boot off it without modifying the bios. Supposedly its possible, but you can easily use one as a storage drive until you upgrade.
 
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VirtualLarry

No Lifer
Aug 25, 2001
56,320
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Supposedly, the 950 Pro M.2 NVMe SSDs, have an "PCI-E Option ROM", that allows them to boot, in systems that normally don't directly support NVMe booting, but do support PCI-E devices. In combination with a PCI-E x4 slot card that is a physical adapter for the M.2 PCI-E NVMe SSD, to connect it to a PCI-E x4 slot on the mobo.

Maybe @cbn will be along to show us a picture of his PCI-E x1 M.2 vertical slot adapters. Seems like the cheapest solution, but then your SSD only connects via PCI-E x1, making it 4x slower for sequential transfers.
 

cbn

Lifer
Mar 27, 2009
12,968
221
106
Maybe @cbn will be along to show us a picture of his PCI-E x1 M.2 vertical slot adapters. Seems like the cheapest solution, but then your SSD only connects via PCI-E x1, making it 4x slower for sequential transfers.

Here is the post where I found out about the adapters.

However, I do not recommend these for general builds because there is no support for the adapter. In fact, I had to benchmark with my system horizontal to do the runs.
 

2Dex

Junior Member
Mar 1, 2019
5
0
6
Supposedly, the 950 Pro M.2 NVMe SSDs, have an "PCI-E Option ROM", that allows them to boot, in systems that normally don't directly support NVMe booting, but do support PCI-E devices. In combination with a PCI-E x4 slot card that is a physical adapter for the M.2 PCI-E NVMe SSD, to connect it to a PCI-E x4 slot on the mobo.

Maybe @cbn will be along to show us a picture of his PCI-E x1 M.2 vertical slot adapters. Seems like the cheapest solution, but then your SSD only connects via PCI-E x1, making it 4x slower for sequential transfers.

Which brings me to question 6 :) : NVMe is a protocol that allows 2 devices to talk to eachother. So is it like a command set/instruction set ? So both devices need to have some sort of NVMe chip/controller where the protocol is stored ? What I'm asking for is that an NVMe PCIe SSD obviously has the NVMe protocol on board. Does the motherboard need an NVMe chip/controller as well or is it sufficient that 1 of the 2 devices has the protocol ?

Also I came across this (discontinued ??) adapter card which uses an PCIe 2.0 or 3.0 x4 connection ! So then in theory full speed would be possible (if mobo would support NVMe).
https://rog.asus.com/articles/produ...pci-express-gen23-to-m-2-x4-ssd-adapter-card/

Also exists in (discontinued??) mini version it seems:
https://www.asus.com/us/Motherboard-Accessories/HYPER_M2_X4_MINI_CARD/
 

2Dex

Junior Member
Mar 1, 2019
5
0
6
1. Yes.

5. This question doesn't make any sense, PCIe slots have nothing to do with SATA. PCIe slots are connected either directly to the CPU or through the chipset (and DMI link to the CPU).
Your motherboard has the two top x16 slots wired directly to the CPU and the bottom one to the chipset.
Some M.2 slots can operate in both NVMe mode and SATA3 mode, but that is manufacturer dependant. On Intel mainstream platforms the M.2 slots are routed through the chipset.

So is this snapshot the way to identify if a certain MB uses NVMe or SATA III protocol for it's M.2 sockets ?
I took a random MB: f.e. https://www.asus.com/us/Motherboards/ROG-STRIX-Z270E-GAMING/specifications/

Blue = NVMe protocol on the M.2 slot (which uses PCIe lanes over the chipset to the CPU) ==> the way to go for better speed/bandwidth
Red = SATA III protocol on the M.2 slot (which uses PCIe lanes over the chipset to the CPU)

M.2 protocol.PNG

Also I read that some M.2 slots are directly connected with PCIe lanes to the CPU (not over the chipset): How would it be written down in the manual ? I haven't come across that yet.
 

mv2devnull

Golden Member
Apr 13, 2010
1,498
144
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Blue = NVMe protocol on the M.2 slot (which uses PCIe lanes over the chipset to the CPU) ==> the way to go for better speed/bandwidth
Red = SATA III protocol on the M.2 slot (which uses PCIe lanes over the chipset to the CPU)
The CPU is linked to the chipset.
* The chipset can have a PCIe x4 link to a M.2 connector. Connected M.2 device would use NVMe
* The chipset has AHCI SATA controller. There can be a SATA link from controller to a M.2 connector. Connected M.2 device would use SATA
* Same M.2 connector can have both links to chipset

Also I read that some M.2 slots are directly connected with PCIe lanes to the CPU (not over the chipset): How would it be written down in the manual ? I haven't come across that yet.
That would be on boards for AMD Ryzen.
 

Campy

Senior member
Jun 25, 2010
785
171
116
So is this snapshot the way to identify if a certain MB uses NVMe or SATA III protocol for it's M.2 sockets ?
I took a random MB: f.e. https://www.asus.com/us/Motherboards/ROG-STRIX-Z270E-GAMING/specifications/

Blue = NVMe protocol on the M.2 slot (which uses PCIe lanes over the chipset to the CPU) ==> the way to go for better speed/bandwidth
Red = SATA III protocol on the M.2 slot (which uses PCIe lanes over the chipset to the CPU)

View attachment 3794

Also I read that some M.2 slots are directly connected with PCIe lanes to the CPU (not over the chipset): How would it be written down in the manual ? I haven't come across that yet.

Funny you should choose that as an example, as it's the motherboard I currently have :)

Yes, it's usually detailed like this. In my experience, most(all?) M.2 ports support NVMe, and sometimes also support SATA3 at the motherboard manufacturers discretion.
If you follow the asterisks to the bottom of the page for the Z270E you will see further details on which ports conflict with others.

Z270E:
*2 The M.2_1 socket shares SATA_1 port when use M.2 SATA mode device. Adjust BIOS settings to use a SATA device.
*3 The M.2_2 socket shares SATA_56 ports when use M.2 PCIE mode device in X4 mode. Adjust BIOS settings to use SATA devices.

So if you use a SATA type drive in the M.2_1 slot, you lose one regular SATA port. If you use two NVMe drives at x4 bandwidth in this board, you lose two SATA ports(5 and 6). However you can also run the M.2_2 slot in x2 mode rather than x4 mode, and retain the use of all SATA ports(one NVMe M.2 at x4, one at x2, and six regular SATA ports).
 

2Dex

Junior Member
Mar 1, 2019
5
0
6
Z270E:
However you can also run the M.2_2 slot in x2 mode rather than x4 mode, and retain the use of all SATA ports(one NVMe M.2 at x4, one at x2, and six regular SATA ports).

:D
Can you show me your sources that make you conclude this ? I cannot find it anywhere and I would like to understand.


Question 2: My motherboard furthermore provides 4 PCIe 2.0 lanes (Not direct to CPU, but rather over the Z68 chipset) ?
Are you realy sure this is correct ? On the block diagram it clearly says 8 PCIe 2.0 slots. It's just that this snapshot makes me think I only have 4 PCIe lanes over the Chipset.
 

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Shmee

Memory & Storage, Graphics Cards Mod Elite Member
Super Moderator
Sep 13, 2008
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Just a heads up, some socket 1155 boards(Z68,Z77), as well as some X79 boards will support either PCIE 2.0 or 3.0, depending on the CPU. This is because 2nd gen core series such as the 2700K you have use a PCIE 2.0 controller on the chip, while 3rd gen CPUs, like a 3770K, use PCIE 3.0 controllers.

Likewise in X79 boards if running a Sandybridge-E chip you get PCIE 2, with Ivybridge-E you get PCIE 3.0
 

mv2devnull

Golden Member
Apr 13, 2010
1,498
144
106
Are you realy sure this is correct ? On the block diagram it clearly says 8 PCIe 2.0 slots. It's just that this snapshot makes me think I only have 4 PCIe lanes over the Chipset.
The block diagram states that you can connect at most 8 PCIe 2.0 lanes to the Z68.
Your motherboard maker has chosen to connect 4 lanes from chipset to three physical PCIe connectors, USB header, and eSATA connector.