Question How come a pcie x1 card is faster in a pcie x8 slot?

[Bassquake]

I have a motherboard which is pci 2.0.

If I put the pcie x1 sata 3 adapter card into the pci x1 slot, I only get about 170MB/s with a sata 3 ssd drive.

If I put the card into a 8x pcie slot, then I get about 450MB/s!

Why would it be different? The pcie-x1 is supposed to be 500MB/s. I dont see why it would be different as the card is fixed at x1 speed. Its not like its using any more pins on the 8x slot!

What gives?

Edit: Sata adapter is in a x16 slot when achieving 450MB/s.

 

[rgd1101]

what is the pcie x1 sata 3.0 adapter. link to it?

and this motherboard make and model

 

[kanewolf]

That x1 slot may share bandwidth with other devices. You would have to look for a block diagram of the motherboard chipset.
The x8 slot probably gets it's PCIe lanes directly from the CPU. But you pay the price of your graphics card running at a max of x8 interface.

 

[Bassquake]

Correction: the sata adapter is in the 2nd x16 slot not x8.

and this motherboard make and model

Gigabyte GA-X58A-UD3R v2.

Ive tried 2 models with same results:

https://www.amazon.co.uk/HILABEE-2Port-Express-Adapter-Profile-Black/dp/B07KP6ZXVY

https://www.amazon.com/Ubit-Express-Expansion-Controller-Adapter/dp/B07HGWZ24M

That x1 slot may share bandwidth with other devices.

I checked the manual, it doesnt say it shares. It mentions the 1st x16 slot (my gpu) shares with the 1st x8 slot but I dont have anything in that.

 

[Bassquake]

You would have to look for a block diagram of the motherboard chipset.

Heres the diagram if its of help:

 

[kanewolf]

And the block diagram shows the x1 slots tied to the ICH and the x16 slots tied to the CPU, just as I said. That explains the performance differences.

 

[molletts]

Reading between the lines in the spec on the Gigabyte website, it would appear that the PCIe x8 and x16 slots are PCIe 2.0 whereas the x1 slots may only be PCIe 1.0, which is consistent with the observed performance.

 

[Bassquake]

Reading between the lines in the spec on the Gigabyte website, it would appear that the PCIe x8 and x16 slots are PCIe 2.0 whereas the x1 slots may only be PCIe 1.0, which is consistent with the observed performance.

Sounds like it. Didnt know could mix specs like that.

The Gigabyte sata and JMicron JMB362 (both sata 2) which shares the same path to the Intel ICH10R. I get about 250MB/s with those.