www.everythingusb.com/forums/showthread.php?threadid=796
Post A Reply Ian Chiu EverythingUSB Managing Editor Registered: Sep 2001 Location: Posts: 1753 OS: Windows XP, Panther How fast is USB 20? USB 20 has a raw data rate at 480Mbps, and it is rated 40 times faster than its predecessor interface, USB 11, which tops at 12Mbps. Originally, USB 20 was intended to go only as fast as 240Mbps, but then, USB 20 Promoter Group increased the speed to 480Mbps in October 1999.
Reply w/Quote jacjud Newbie Registered: Dec 2002 Location: Posts: 1 OS: windows XP Is the 480 the total bandwith available to all connected devices who must share the bandwith? If we attach a Hub with power will it provide each device with maximum bandwith, or is it just a convenience to attach more devices to share. When you connect a usb 11 device to a usb 20 hub, does it slow down all other USB 20 devices to only share the 11 bandwith? I can't find an answer to this in any cards or motherboard manuals.
Reply w/Quote Ian Chiu EverythingUSB Managing Editor Registered: Sep 2001 Location: Posts: 1753 OS: Windows XP, Panther quote: Originally posted by jacjud When you connect a usb 11 device to a usb 20 hub, does it slow down all other USB 20 devices to only share the 11 bandwith? Connecting a USB 11 device to a USB 20 hub won't slow down everything to USB 11 speeds. I have a USB mouse, a USB 11 card reader and USB 11 scanner all sharing the same hub with my USB 20 hard drive and video capture device. Ian Chiu Please do not use Private Messaging to ask technical questions.
Reply w/Quote zoom USB Guru Registered: Jan 2002 Location: Posts: 199 OS: Winxp quote: If we attach a Hub with power will it provide each device with maximum bandwith, or is it just a convenience to attach more devices to share. some newer USB 20 hubs provide each port with full 12Mbps USB 11 bandwidth wheres most 1st gen. As for USB 20, the hi-speed devices have to share all available bandwidth (480Mbps).
Reply w/Quote Ste8534 Newbie Registered: May 2003 Location: Posts: 3 OS: Windows XP Home Question OK SO WE KNOW THAT USB 20 CAN PROVIDE A 480MB MAX DATAPIPE POWERED OR UNPOWERED. WHAT IF I ADD A DEVICE THAT REQUIRES A 100MB TRANSFER RATE AND ANOTHER ONE THAT REQUIRES SAY A 50MB TRANSFER RATE.. IS USB 20 480MB MAX TRANSFER RATE 12MB TRANSFER RATE WHEN MORE THAN ONE 20 DEVICE IS ADDED OR IS IT 480MB TRANSFER RATE ON DEMAND TO WHERE ANY DEVICE CAN DEMAND WHAT IT WANTS SO LONG AS ALL THE 20 DEVICES DO NOT REQUEST MORE THAN 480MB IN ADDITION, DO ADDING 11 DEVICES TO THIS 20 HUB LIMIT THE 20 ABILITIES IN ANYWAY.
Reply w/Quote billyd Forum Moderator USB Tech Specialist Registered: Jan 2002 Location: Posts: 5629 OS: All Windows Didn't you know that it's rude to type in ALL CAPS, Steve? Besides, MB(Bytes) per second and Mb(bits) per second are two very different measurements. William DeVercelly Windows 2000 MCSE/MCP and USB Retail Specialist/Troubleshooter Please update your virus protection, visit Windows Update and beware that overclocking your CPU can cause odd USB behavior! Please do not use Private Messaging to ask technical questions.
Reply w/Quote Ste8534 Newbie Registered: May 2003 Location: Posts: 3 OS: Windows XP Home yesss your right, i apologize for that.. i thought a saw a post in caps and it just seems that the type is sooo light..
Reply w/Quote billyd Forum Moderator USB Tech Specialist Registered: Jan 2002 Location: Posts: 5629 OS: All Windows Ok then - the way USB 20 works is that you have one chip with three host controllers. Two of them are USB 11 and one is USB 20 Signals are routed as needed to the correct controller. If you have 2 USB 11 devices, they will each get the full 12Mbit/s. Add a USB 20 device and it's routed to the Enhanced controller all by itself for a full (theoretically) 480Mbit/s. In this scenario, bandwidth is not limited for the high-speed device, however, add another high-speed USB device, operate the two of them simultaneously and you will see bandwidth limitation. This is an unlikely scenario because most people don't try to operate both at the same time. William DeVercelly Windows 2000 MCSE/MCP and USB Retail Specialist/Troubleshooter Please update your virus protection, visit Windows Update and beware that overclocking your CPU can cause odd USB behavior! Please do not use Private Messaging to ask technical questions.
Reply w/Quote Ste8534 Newbie Registered: May 2003 Location: Posts: 3 OS: Windows XP Home Question See, I theorized this.. what if they come out with say an HDTV capture device that say needs a 25mb transfer rate, then you need to add the DVD burner that need a good 16mb or better transfer rate to the same USB 20 port, maybe you even added more hard drive space, which can use say 100mb/s transfer rate. At some point all these devices might get used in conjunction say to capture video and burn it at a high demand rate. I'm just wondering if USB 20 can do this cause someone told me that USB 20 will only give you either 480mb/s for the 1st USB 20 device added or if more than one USB 20 device is as in the example above, they'll each only get 12mb/s and if thats the case the above ideas for devices could never work. Just curious cause I have a laptop and i just want to make sure that there will be plenty of external bandwidth from it and also which ways to grow, USB 20 or firewire. I like USB cause you don't need to buy a new type of hub or wires do to their backward capatability.
Reply w/Quote billyd Forum Moderator USB Tech Specialist Registered: Jan 2002 Location: Posts: 5629 OS: All Windows Well, I can tell you that it's not all or nothing. William DeVercelly Windows 2000 MCSE/MCP and USB Retail Specialist/Troubleshooter Please update your virus protection, visit Windows Update and beware that overclocking your CPU can cause odd USB behavior! Please do not use Private Messaging to ask technical questions.
Reply w/Quote humpty Newbie Registered: May 2004 Location: Posts: 1 OS: win98se, 2K, XP USB 20, It's a big CON. This should be made clear to potential users instead of being shoved under the carpet.
Reply w/Quote billyd Forum Moderator USB Tech Specialist Registered: Jan 2002 Location: Posts: 5629 OS: All Windows All PC interfaces come up short of their theoretical maximums. When was the last time you saw a UDMA133 hard drive transfer data higher than 50MB/s steady-state? William DeVercelly Windows 2000 MCSE/MCP and USB Retail Specialist/Troubleshooter Please update your virus protection, visit Windows Update and beware that overclocking your CPU can cause odd USB behavior! Please do not use Private Messaging to ask technical questions.
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