USB Increased Speed

[vol7ron]

So I was reading about USB 3.0 and started thinking about USB 2.0 again.

The theoretical speed is 480 Mbit/s, but is that the usual bus speed that it sits on, or is that the maximum speed per device? If two USBs share the same bus is it possible for them both to act at 480 Mbit/s on the same bus.


I think my motherboard has two different busses, for different USBs. So I was curious if there is a USB adapter/controller to split my one device across both busses in order to double the speed.

 

[vol7ron]

I guess this is not a concern for some, but if there is such an external controller/adapter, when USB 3.0 is standardized (5 Gbps), I'm looking at a possible Gbps (2x5Gbps) possibility. External SSDs HD, or even thumb drives, might seem a viable alternative for OSs.

The wave of the future is a 12-16 USB port mound the size of your fist, housing an integrated cpu/gpu, allowing you to carry your OS/data wherever you go.

What do you think?

 

[jimhsu]

Latency, not bandwidth ... even if you had a 100 Tbps connection, the distance from the proposed CPU to the rest of your computer is probably too great. Nanoseconds do matter here...

 

[Modelworks]

I know someone testing USB 3.0 . From what I have been told it has problems with the length of the cable and the quality of the cable. There are also issues with usb 2.0 devices sharing the bus, some are not recognized. It could be great when all the bugs get worked out. The comment I got from him was "When it works, it is great !"

Which isn't very enthusiastic.

 

[vol7ron]

Granted, latency is important, but at the moment the throughput is the problem. I imagine the latency will improve after restructuring. Right now, there's no need.

Streaming HD video is right around the bend though

 

[lopri]

There is also the limit of a chipset. Most (all?) chipsets have a hard limit on total USB bandwidth. I believe it is somewhere around 100~120 MB/s currently.

 

[vol7ron]

So then that's the bus speed? Regardless, this is dependent on manufacturer and will increase as the USB devices are able to transmit faster. As noted in my first post, though, my mobo has two different bus lines; which is why i'd like some way of bridging them.

 

[Sahakiel]

If I remember correctly, USB is a shared bus similar to Ethernet. However, I don't think anyone added aggregation to the spec. It was designed from the beginning to be simple to use, easy to implement, and cheap to produce. Technically, you can have up to, I think, 255 devices hanging off one bus. USB 2 specifies up to 480 Mbps, so unless you're only using it for far too many keyboards, it's probably not very fast.

The reason your motherboard seems to have different bus lines is due to the low cost of USB. Since it's cheap to produce, your mobo manufacturer put in separate buses to split the load so different USB devices can run with less traffic. In contrast, I recall Firewire is be point-to-point, so individual devices can talk to each other without involving your "host" computer. Even though each link is limited to 400Mbps, less bandwidth is taken up talking to your PC and consuming CPU cycles.

In theory, any USB device can saturate the bus, so adding multiple separate buses is the easiest way to have load balancing. The user can add quite a few devices before typically seeing any slowdown. If you've ever been lazy (like me) and transferred files between a couple external hard drives instead of hooking them up to extra SATA ports, you can easily measure the difference in bandwidth between having both on one bus vs using two.

As for the future of USB, I see a different future. From conception, USB was meant for attaching peripherals. If you don't have peripherals, there's no reason to have a port to connect them.

 

[VirtualLarry]

My understanding is that the 480Mbit/sec bandwidth is per-controller. Since most PCs have only a single Enhanced PCI USB controller (USB2.0), that means that ALL USB2.0 devices SHARE that total bandwidth. A USB external hard drive usually maxes out at around 28MB/sec for a single HD. It would be interesting to benchmark multiple external USB HDs all at once, and see what kind of bandwidth you can get.

 

[Modelworks]

Originally posted by: VirtualLarry
My understanding is that the 480Mbit/sec bandwidth is per-controller. Since most PCs have only a single Enhanced PCI USB controller (USB2.0), that means that ALL USB2.0 devices SHARE that total bandwidth. A USB external hard drive usually maxes out at around 28MB/sec for a single HD. It would be interesting to benchmark multiple external USB HDs all at once, and see what kind of bandwidth you can get.

It is per port on the controller. Port meaning the actual pin that the usb connects to on the controller chip itself, not the connectors on the motherboard. Really depends on the board.

Mine has 2 usb2.0 controllers.

 

[jimhsu]

We need fiber optic USB 3.0 cables ... God knows how much they cost though.

 

[yh125d]

Originally posted by: vol7ron

Streaming HD video is right around the bend though

You can already do that via USB 2.0