USB 3.0 Speed on PCIe 2.0 x1 Slot

[PalaDolphin]

Q: Do I have to buy an entirely new motherboard or is there an expansion card that supports USB 3.0 speeds in a PCIe x1 2.0 slot?
I have an existing Seagate 3TB USB 3.0 (with blue connector) HD; it's currently connected to a USB 2.0 port. I want it to perform at maximum speeds of 4.8 Gpbs.
I just bought a used HP Pavilion P7-1254 desktop. It only has USB 2.0 ports and PCIe 2.0 slots (1 - x16, 3 - x1). Since I'm reserving the x16 slot for a video card upgrade I'm only looking for a USB 3.0 PCIe x1 host card. If what I understand is correct, PCIe 2.0 x1 has a speed of 500 MB/s which is comparable to USB 2.0 speeds. A USB 3.0 card that is limited to 500 MB/s may be compatible but defeats the entire purpose of the expansion: 10x speed increase.

 

[Barty1884]

USB is still a somewhat limiting factor. A 3.0 drive won't saturate a gen2 x1 slot speeds, despite having (slightly) faster speeds, theoretically.

While USB 2.0 has a max theoretical 60MBps speed, 3.0 has 640MBps, although you'll never actually see those speeds in 'real world' usage.

Gen2 PCIe x1 has max theoretical of 500MBps, so while you're never likely to saturate that (and a 3.0 drive won't transfer a 640MBps), a 3.0 addon card in a PCIe Gen2 x1 slot will still be dramatically faster.

 

[boosted1g]

Worrying about USB 3.0 speed for a magnetic hard drive is like worrying about putting 170mph rated tires on a small 3 cylinder car.
Your magnetic hard drive at best will see 120 MBps (or 1gbps) so the fact that the x1 slot can only support 500MBps is irrelevant for your purpose.

 

[PalaDolphin]

So, you're thinking double the speed as opposed to the 10x that is regularly touted of USB 2.0 vs 3.0?

 

[TJ Hooker]

Your magnetic hard drive at best will see 120 MBps (or 1gbps) so the fact that the x1 slot can only support 500MBps is irrelevant for your purpose.

So, you're thinking double the speed as opposed to the 10x that is regularly touted of USB 2.0 vs 3.0?

If that. You'd probably only see speeds up around 120 MB/s for sequential transfers; random will be slower. Also, external USB HDDs tend to be slower in general.

Unless you're transferring a lot of large files to that HDD fairly often, I'd question whether getting a USB 3.0 add in card will provide any significant benefit.

Edit: Hmm, USB 2.0 is slower than I thought. Apparently max theoretical throughput is 60 MB/s, but practically only gets up to 35 MB/s. You should see some improvement moving to USB 3.0.

 

[boosted1g]

So, you're thinking double the speed as opposed to the 10x that is regularly touted of USB 2.0 vs 3.0?

No no no.

I am saying that the speed of native USB 3.0 vs speed of PCI-X1 USB 3.0 is irrelevant for your purpose. The hard disk drive can only physically access the data from its platters so fast and thus will max out at around 120 MBps. So since the data leaving the port on the hard drive tops out at 120 MBps, whether you are on a 500MBps (PCIx1) interface or 640 MBps (native USB 3.0) interface is irrelevant. That is why i made the car reference, if the small 3 cylinder car tops out at 80 mph then it is pointless to worry about whether to get 150 mph rated tires or 170 mph rated tires because the car can never get close to that speed.

 

[TJ Hooker]

@boosted1g he's talking about the increase in speed he'll see from moving from USB 2.0 to (PCIe x1) USB 3.0. Given the speed of USB 2.0, it's reasonable to think he could more than double his throughput, at least for sequential transfers.

 

[boosted1g]

@boosted1g he's talking about the increase in speed he'll see from moving from USB 2.0 to (PCIe x1) USB 3.0. Given the speed of USB 2.0, it's reasonable to think he could more than double his throughput, at least for sequential transfers.

Aww.

 

[PalaDolphin]

So, you're thinking double the speed as opposed to the 10x that is regularly touted of USB 2.0 vs 3.0?

No no no.

I am saying that the speed of native USB 3.0 vs speed of PCI-X1 USB 3.0 is irrelevant for your purpose. The hard disk drive can only physically access the data from its platters so fast and thus will max out at around 120 MBps. So since the data leaving the port on the hard drive tops out at 120 MBps, whether you are on a 500MBps (PCIx1) interface or 640 MBps (native USB 3.0) interface is irrelevant. That is why i made the car reference, if the small 3 cylinder car tops out at 80 mph then it is pointless to worry about whether to get 150 mph rated tires or 170 mph rated tires because the car can never get close to that speed.

This sucks because I cannot find any MBps specs on my Seagate drive. I should just find someone with a similar system with USB 3.0 ports and test it. The other thing is I have another reason to upgrade the motherboard: I want at least 16GB RAM; mine is limited to 8GB.