[ryarber]

Seems that I have read that if you have a USB 1.1 device on a USB 2.0 bus, that slows the entire bus down to 1.1 speed. Is that true? Does the Powermac G5 have 3 separate busses so that if I want to use one for USB 1.1 devices I can still have two busses free for the 2.0 spec?

Another question... Are the Apple cinema displays built in USB hubs 1.1 spec or will they support 2.0 spec? Does anyone know which bus the monitor is on? If I plug a USB 1.1 device into the monitor, which bus will this effect?

[tooki]

It is NOT true. USB 1.1 and 2.0 devices can coexist peacefully.

The G5 has 3 ports, each of which is dynamically routed to one of 2 USB 1.1 or the one USB 2.0 controller inside the USB chip as needed, depending on what device is plugged in.

tooki

[Arkham_c]

It's true, but there are workarounds. The G5 has at least two USB busses (one in front, on in back). Here is the USB FAQ:

http://www.everythingusb.com/usb2/faq.htm

Here is a specific quote:

What happen if a USB 2.0 device is plugged into a USB 1.1 system?
The entire bus under the USB 1.1 root hub will slow to 12Mbps. The operating system will probably notify the user about the sub-optimal configuration and recommend for a better course of action.

It's my understanding that if you buy a USB 2.0 hub, and you plug a 1.1 device into the hub, the rest of the hub's ports will continue to run at 2.0 speeds.

[Simon]

Ah, darn. Does a 1.1 device sitting on the same bus (or same hub?) now slow down the 2.0 device or not? You sure feel USB wasn't developed by Apple. This sounds much to uncomprehensible.

Does SystemProfiler show at which USB speeds the different devices are running, ie. 12Mbps or 480Mbps? That way we could at least try to switch stuff around until we find that high-bandwidth devices aren't being slowed down just because the keyboard happens to sit on the same USB controller.

[chabig]

It is NOT true. USB 1.1 and 2.0 devices can coexist peacefully.

Yes they will coexist. It is a fallacy that the entire bus will be slowed down the 1.1 speeds, but the 2.0 devices will have reduced throughput.

All three USB ports on the G5 are USB 2.0 ports. The hubs that are built into the monitor and keyboard are 1.1 hubs. The best way to handle 1.1 devices is to plug them into a USB 2.0 hub and then plug the hub into the computer.

Chris

[ryarber]

Originally posted by chabig:
Yes they will coexist. It is a fallacy that the entire bus will be slowed down the 1.1 speeds, but the 2.0 devices will have reduced throughput.

All three USB ports on the G5 are USB 2.0 ports. The hubs that are built into the monitor and keyboard are 1.1 hubs. The best way to handle 1.1 devices is to plug them into a USB 2.0 hub and then plug the hub into the computer.

Chris

Thanks, Sounds like I'll need to plug my USB 1.1 devices (eg. bluetooth adapter, mouse, etc.) into the monitor or keyboard and buy another USB 2.0 hub for other, higher bandwidth devices.

Thanks to all for the information

[tooki]

Originally posted by Arkham_c:
It's true, but there are workarounds. The G5 has at least two USB busses (one in front, on in back)

It is NOT TRUE!!!

From the G5 Developer's Tech Note PDF:

USB Ports
The Power Mac G5 computer has two external Universal Serial Bus (USB) 2.0 ports
on the back and one on the front of the enclosure and an internal connection to the
AGP slot for the Apple display. The external USB ports are off of the USB controller
connected to the PCI bus, bridged by K2. In addition, there are two USB 1.1 ports on
the keyboard. The USB ports are used for connecting the keyboard and mouse as
well as additional I/O devices such as printers, scanners, and storage devices.
All USB ports are fully compliant with the USB 2.0 specification, including support
for high-speed (480 Mbps) devices using an Enhanced Host Controller Interface
(EHCI). Ports are automatically routed to a companion OHCI controller when a
classic-speed (full-speed or low-speed) USB device is attached to a root hub port.
Each USB rear port is connected to a separate USB root hub in classic speeds,
allowing the USB ports to support 12 Mbps devices at the same time with no
degradation of their performance. The USB root hubs are also connected to the
internal USB modem and to the USB port on the ADC monitor connector.
The three external USB ports and the port supporting the Apple display comply
with the Universal Serial Bus Specification 2.0. The two ports on the keyboard
comply with the Universal Serial Bus Specification 1.1 Final Draft Revision. For low-
speed and full-speed devices, the USB register set complies with the Open Host
Controller Interface (OHCI) specification. For high-speed devices, the USB register
set complies with the Enhanced Host Controller Interface (EHCI) specification.
For more information about USB on Macintosh computers, please refer to Apple
Computer’s Accessing Hardware from Applications and the other sources listed in
“USB Interface” (page 82).

In other words, what I said above. (= The G5 has 3 USB buses -- one 1.5/12/480Mbps bus and one 1.5/12Mbps bus. All three ports connect to all 3 buses inside the USB chip, which automatically routes the external port to the most appropriate controller.)

tooki

P.S. The G5 also has two "private" USB buses for the modem and Bluetooth module. These buses have no external connectors at all.

[himself]

Originally posted by tooki:
...P.S. The G5 also has two "private" USB buses for the modem and Bluetooth module. These buses have no external connectors at all.

Don't forget the USB bus on the ADC... that wouldn't be 2.0 as well, would it?

[ryarber]

Originally posted by himself:
Don't forget the USB bus on the ADC... that wouldn't be 2.0 as well, would it?

I think what they're trying to say is that the USB bus going to the display are USB 2.0 compliant. However, the current monitors themselves only support the 1.1 spec. Therefore, this renders anything you plug into the monitor to run at USB 1.1 speeds (ie. 1.5/12 and not 480Mb/s).