USB2 Specs Are In

PooF writes "USB 2.0 has been announced. It seems sweet, its faster than firewire at 480 Mb/s. An article from pc.ign.com on USB 2.0. Oh yea these are only the specs they hope to achieve no word on progress in implementing them."

Comments

Re:BFHD

[kroah]

OK, I'm actually at the USB 2.0 Devcon right now, and have read the 2.0 proposed spec, so I'll take a stab at refuting these comments:

1.The usb.org article only claims "120-240Mbps". It's not clear where the ign.com article came up with 480Mbps.
The speed is 480Mbs. That is what the spec says.

2.Even if USB2 runs at 480Mbps, the Firewire folks aren't exactly standing still. Any raw bandwidth advantage of USB2 is sure to be short-lived at best.
Firewire and USB have too many things that are not in common, they really are not competitors. USB is aimed to be a PC centric bus. There has to be only one host, and a whole lot of clients. Firewire can be host to host. Firewire is more intrenched in the consumer electronic market, while USB is sticking to the PC (for now).

3.There's lots of blather in the USB2 announcement about supporting video cameras etc. but IIRC USB doesn't support the isochronous transfers which are usually considered necessary to serve those markets. Did I miss something?
You missed something. USB has always supported isochronous transfers. Look at the USB speakers from Philips for an example of a shipping product that uses this. Isochronous is still there for 2.0.

4.Another useful Firewire feature that USB doesn't seem to have is providing power through the same connector used for communications. Again, I may have missed it.
USB has ALWAYS supported power on the connector. How else does some of the devices work? 2.0 does not change this. It's still 5V at 100mA-500mA depending on what you need and ask for. If you need more power, take a look at the Plus Power Connector that IBM supports for USB. It can provide 12V or 24V at 3A. That's about all the current that anyone needs.

5.I don't remember how many devices USB supports, but I suspect it's less than Firewire.
USB supports 127 devices per host controller. You can plug in more than one host controller in your PC at a time. The record (I think) for most devices plugged in and working at once is around 144.

6.I know that USB-based host-to-host networking exists, but it's not clear to me whether it's really as well suited to that task as Firewire. In particular, I wonder how much asymmetry between hosts and devices (a la initiators and targets in SCSI) is built into the protocol, and how round-trip latency compares to other technologies.
As I said above, USB is a host-client bus. You can make (and buy) a device that does networking over USB from one computer to another, but this is just two client devices talking together in a box. Firewire can do true host to host on the bus itself. The USB protocol is a star topology with the PC host controller at the top. I can look up the round trip latency stuff somewhere, but it is built into the protocol, and the host and hub controllers seem to handle it well.

7.Similarly, I'd like seeing a comparison of how automagically reconfiguration happens when devices are added or removed using each technology.
I don't really know how Firewire does this at all, but USB handles this wonderfully. There is a description of how the protocol handles all of this in the spec (at www.usb.org).
In summary, USB 2.0 looks like it handles a lot of the speed issues that some people had with 1.1. It provides backward compatibility with all 1.1 and 1.0 devices and enables things like speakers and video cameras to run better.
Like it or not, USB looks to be here for a while. A lot of computers are coming out without a lot of different connectors, and USB is replacing them.

Ob Linux: USB is working on Linux in the 2.3.x series of kernels (it's also supported a little in the 2.2.x series, but not for many devices.) More information is at www.linux-usb.org

BFHD

[Salamander]

Just a few observations/questions regarding comparisons with Firewire.

1. The usb.org article only claims "120-240Mbps". It's not clear where the ign.com article came up with 480Mbps.
   
2. Even if USB2 runs at 480Mbps, the Firewire folks aren't exactly standing still. Any raw bandwidth advantage of USB2 is sure to be short-lived at best.
   
3. There's lots of blather in the USB2 announcement about supporting video cameras etc. but IIRC USB doesn't support the isochronous transfers which are usually considered necessary to serve those markets. Did I miss something?
   
4. Another useful Firewire feature that USB doesn't seem to have is providing power through the same connector used for communications. Again, I may have missed it.
   
5. I don't remember how many devices USB supports, but I suspect it's less than Firewire.
   
6. I know that USB-based host-to-host networking exists, but it's not clear to me whether it's really as well suited to that task as Firewire. In particular, I wonder how much asymmetry between hosts and devices (a la initiators and targets in SCSI) is built into the protocol, and how round-trip latency compares to other technologies.
   
7. Similarly, I'd like seeing a comparison of how automagically reconfiguration happens when devices are added or removed using each technology.

With any luck, someone more clueful can fill in the blanks above.

Overall, Firewire still looks like a generally superior technology in its niche, while the USB folks should have been content with their own separate niche (lower-bandwidth peripherals such as keyboards, mice, joysticks and modems that don't need advanced features such as isochronous transfers).

BTW, I don't actually use Firewire and have no interest beyond the aesthetic in promoting it. My employer is thoroughly committed to (ick) FC.