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My mainboard is a Gigabyte EP45-UD3R. It has 3 x PCIe x1 slots and 1 x PCIe x16 slot. It specifies that the x16 conforms to PCIe 2.0 standard but does not specify if the x1 slots are 1.0 or 2.0. This is a Windows 7 64 bit system and I am using USB 3.0 Cables.

From what I found online, even if it’s 1.0, it should have throughput of 500 MB/s total both ways (250 MB/s send and receive). While this falls short of USB 3.0’s potential, it is much faster than USB 2.0 and gives a noticeable performance boost over 2.0 with mechanical hard drives. So it's perfectly fine for what I had been using it for. I get about 100 MB/s read/write speeds on the external mechanical drives I used with it, which is the most I could hope to get from those drives. However, I recently connected an SSD to to my USB 3.0 controller card and the speeds are… the same as they are with my mechanical HDD, about 100 MB/s read/write.

The USB 3.0 controller I’m using is a SIIG JU-H40411-S1. That’s the model anyway, the actual controller is a Renesas, but I’m not sure how to get it’s exact model. The USB 3.0 to SATA controller that I’m using is the one that came with my Seagate GoFlex drive and this works at much faster speeds on another computer with USB 3.0 build into the board, around 250 MB/s (although that still falls short of the drives rated performance, it’s over twice the speed I'm getting on my computer).

I really don’t get it though… Even if my PCIe x1 slots are only 1.0, they should have a theoretical maximum bandwidth of 250 MB/s, and probably about 200-220 realistically. But I’m not getting anywhere near those speeds. So what is going on here that I'm missing? Any ideas?

EDIT: (additional information/follow up question) I know this doesn't really fit into the theme of this site's flow, but I am very confused and really would like to ask a follow up question that won't fit in the comment box. I hope that is not looked down upon. I would ask a new question but I don't feel like asking an entirely new question with these new details would be the best thing to do (or maybe it would, but I'm not sure so please go easy on me if I messed up big time here.)

I'm a bit confused from what you said, David, and I am hoping you could maybe give some clarification based on my follow up question here? I have 6 SATA ports that are controlled by the ICH10R and they give me about 250 MB/s read/write. So I am not sure how the south-bridge can be the bottleneck when I get relatively good performance with it's integrated SATA controller (although curiously enough, that 250 MB/s falls short of SATA 2's rated 3 Gbps by quite a lot). That being said, I do have 3 PCIe x1 slots, the RTL 8111C Gigabit controller, and the GIGABYTE SATA2 controller (with 1 IDE port and 2 SATA ports) that are all apparently using the one PCIe Bus from the southbridge. But of all these ports, I only have the one USB 3.0 controller in one of the x1 slots, a network cable to the gigabit controller, a blu-ray drive on one of the GB SATA2 ports, and an old slow mechanical HDD on the other GB SATA2 port.

None of these devices should be using very much bandwidth; the old HDD has no paging file on it (and I never use it for anything else), the Blu-ray drive is not in use, the Network controller is also barley being partially utilized (very small network amounts of network traffic) and of course the USB 3.0 controller has nothing connected to it other than the SSD. While I understand these devices are not just "dead" when not in use, I can't imagine the little bit of activity they would be participating in would eat up so much bandwidth, that I can only get 100 MB/s from the one very active device. I'm really curious as to what's going on here. It almost seems as if the actual PCIe Bus is the bottleneck, except that as best as I can tell, it's barely being utilized. I appreciate your time and help in this matter, very much!

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    Am I missing something here? Why am I apparently not allowed to thank people for their time? What in the world is wrong with that?
    – Soundfx4
    Sep 21, 2015 at 6:55
  • "250 MB/s falls short of SATA 2's rated 3 Gbps by quite a lot". Actually no. 3.0 gigabit/sec signaling speed is not the same as 3.0 gigabit/sec data transfer. Highest speeds I have seen thus far are ICH10 chipset with SSD at 270MB/sec. Which is close to your 250MB/sec.
    – Hennes
    Sep 21, 2015 at 20:33
  • oh sweet. That's good to know :) I had always figured at 3 Gbps, it's max would be, well 357.6 MB/s and a realistic of about 300-320. But looks like it's max is an actual 2.4 Gbps or 300 MB/s and about 250 MB/s-270 realistic. This is good to know! Thank you!
    – Soundfx4
    Sep 21, 2015 at 21:34

1 Answer 1

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Your PCI Express x1 slots are version 1.1 and connect to the southbridge along with almost everything else in your computer other than memory and the PCI Express x16 slot. So you have massive bottlenecking. The P45/ICH10 was not designed to support high-speed devices connected to ports other than the x16 slot.

If you don't care about graphics performance, you can put the USB 3.0 adapter in the PCI Express x16 slot. This is a PCI Express 2.0 port that's connected directly to the northbridge.

Basically, your motherboard just isn't made for this. If it was, it would have split the northbridge's x16 port into two x8 ports, leaving you a high-speed port for both the USB 3.0 adapter and the graphics card.

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  • Thanks! I have a bit of a follow up question that I edited into my original question, if you don't mind. I upvoted your answer also, btw, but it seems it won't count until I receive 15 rep.
    – Soundfx4
    Sep 21, 2015 at 20:30
  • @Soundfx4 The bottleneck is inside the southbridge, in the way it connects the PCI Express lanes to its internal crossbar. 4KB IOPS are limited to about 10,000 and bandwidth to about 108MB/s. Sep 21, 2015 at 21:39
  • ahh, I got ya! Well that's super lame, and frustrating (it is an 8 year old board though :P), but I understand now. Thanks! :D
    – Soundfx4
    Sep 21, 2015 at 22:14

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