Measure USB port speed?

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Level 1

64 points

Measure USB port speed?

I have a new USB hub (Dlink) that supports USB 1 and USB 2. Unfortunately, plugging in a USB 1 device along with a USB 2 device MAY (their words) cause ALL plugged in devices into the hub, be they USB 2 or USB 1, to run at the slower USB 1 speed.
I would like to KNOW HOW I can tell if my particular hub is doing this slow-down ie will my USB 2 device still run at full speed even though a USB 1 device is plugged in.
Basically, just HOW do I measure the SPEED of the USB port on the hub (which is of course plugged into my Intel iMac 24inch).

Thank you for your consideration in helping me solve this problem...

MacBook, iMac 24" Mac OS X (10.4.8)

MacBook, PowerMac, Mac OS X (10.4.8)

Posted on Oct 28, 2006 9:21 PM

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Answer 1

Top-ranking reply

John M Rivera

Level 2

175 points

Oct 29, 2006 4:29 PM in response to MCKravMaga

ANYWAY, I still need a way to know "fer sur" whether
the port is able to handle both USB 1 and USB 2 at
the same time at the appropriate speeds!

So why don't you just test it? Plug a USB 2 hard drive into one port and an older USB 1 device into another port. Send a large file to the USB 2 device. The difference between a 12 Mbps transfer and a 480 Mbps transfer should be glaringly obvious.

20" iMac CD (early '06) Mac OS X (10.4.8)

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Answer 2

Oct 28, 2006 9:34 PM in response to MCKravMaga

well, if you have a usb flash drive they look like this http://www.livedigitally.com/wp-content/bothdrives800.jpg
put it in the usb port on the keyboard if you have the apple pro keyboard copy files and such. then try it on the usb ports on your mac itself. thats how i would test it

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Answer 3

MCKravMaga Author

Level 1

64 points

Oct 29, 2006 8:30 AM in response to Christopher Neufeldt

Thank you for your reply. I'm afraid I wasn't clear enough in my post though...
I need to test the ACTUAL SPEED of the port, NOT if the port (hub) is working or not.

The hub port can run at various speeds, depending on if you are using a USB 2 device or a USB 1 device. My question is to see if the ENTIRE HUB (all ports on the hub) regardless of USB 2 or USB 1 runs at USB 1 speeds if a USB 1 device is plugged in ANYWHERE on the hub.

Thank you

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Answer 4

MCKravMaga Author

Level 1

64 points

Oct 29, 2006 2:11 PM in response to Christopher Neufeldt

Unfortunately, that is not quite true. On many USB hubs, even though you would like to think that USB 2 devices will always run at USB 2 speeds, the reality is that the single USB 1 device plugged into the hub FORCES the ENTIRE HUB to run at USB 1 speeds. This is NOT, however, clearly stated in the manufactures manual (in my manual, it states that the speed MAY drop!) It depends on the SPECIFIC IC's used and apparently they can vary depending on batch.
ANYWAY, I still need a way to know "fer sur" whether the port is able to handle both USB 1 and USB 2 at the same time at the appropriate speeds!

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Answer 5

Oct 30, 2006 5:37 AM in response to Leo Bodnar

Thank you for this information.

Could you please elaborate on how the USB 2.0 ports on a recent Mac computer would work. Does each port have its own bus? If not, are all ports on the same bus? This would constitute a hub, I suppose, and is not what I would expect from Apple.

If I plug a 1.1 or low-speed device into one of the rear ports on my iMac Intel Core 2 Duo, will it affect (i.e., slow down) the data transfer rate of another device (rated as high-speed) in the adjacent port?

iMac Intel Core 2 Duo 20" Mac OS X (10.4.8) 1 GB ram

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Answer 6

Oct 29, 2006 10:07 AM in response to MCKravMaga

as long as the hub is plugged into a usb2 port its usb2 all ports. what i ment is to give you a feel of what usb2 and 1 are like

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Answer 7

Oct 29, 2006 7:48 PM in response to MCKravMaga

like i ment to say all ports will be usb2 as long as its in a usb2 port

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Answer 8

Oct 30, 2006 4:00 AM in response to MCKravMaga

I am a USB hardware developer if this helps... USB is reasonably complicated concept and is often misunderstood.

USB 1.0, 1.1 and 2.0 are nothing more than specification versions and do not define device speed. Current version is USB 2.0 and previous ones are obsolete.

USB 2.0 compliant device can be low-speed 1.5Mbps device, full-speed 12Mb device or high-speed 480Mb. All modern devices are supposed to be built to USB 2.0 spec and should proudly carry USB 2.0 logo, even if they are simplest dumbest low-speed devices.

Just plugging a low-speed device won't slow the system down
but if there is a lot of traffic between it and the host, this might block other devices from using the shared USB host resource. This is a hub, not a switch so it does not store and forward packets like a switch on Ethernet network.

USB has some protocol overheads so don't expect your actual DATA transfer rates to be equal to bus signalling rates. E.g. maximum theoretical throughput for low-speed (1.5Mbps) device is only 48 KBytes/sec, 1.2 MBytes/sec for full-speed (12Mbps) and 53MBytes/sec for high-speed (480Mbps.) Very few devices actually achieve this as it needs highest degrees of coordination between device and the host.

Out of curiosity you might want to look at basic USB 2.0 spec in http://www.usb.org/developers/docs/usb2005122006.zip
It does not include device classes (HID, storage, comms, etc)

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