USB 2 Maximum Cable Length

zazal · November 19th, 2007

My backup device is a USB 2.0 250 MB Iomega Hard Drive.I'd like to put
it in my garage, requiring about 20 to 25 feet of wire. The official
USB specs say 5 meters max; if further use a hub/repeater.

I'm wondering how realistic the 5 meter spec is. I recall that parallel
printer cables were supposed to be limited to 10 feet or so; 75 foot
cables worked just fine. Same thing with the specs for RS-232 cables.

Does anyone have any real world experience with long USB 2.0 cables?
I'm thinking of building mine using unshielded CAT5 cable, one twisted
pair for power, another for data. Wise? foolish?

**fitz** · November 19th, 2007

personally, I wouldn't do it. As it's your backup device, would you want to risk data loss and/or data corruption caused by signal degradation onto a backup device?

A printer is one thing to try to stretch the distance limit.. a Hard drive and backup data is entirely different.

Go buy a USB hub, put it somewhere in between and get two 5m cables.

http://www.usb.org/developers/usbfaq/#cab1

1. Why are there cable length limits, and what are they?
A: The cable length was limited by a cable delay spec of 26ns to allow for reflections to settle at the transmitter before the next bit was sent. Since USB uses source termination and voltage-mode drivers, this has to be the case, otherwise reflections can pile up and blow the driver. This does not mean the line voltage has fully settled by the end of the bit; with worst-case undertermination. However, there's been enough damping by the end of the bit that the reflection amplitude has been reduced to manageable levels. The low speed cable length was limited to 18ns to keep transmission line effects from impacting low speed signals.

2. I want to build a cable longer than 5 meters, why won't this work?
A: Even if you violated the spec, it literally wouldn't get you very far. Assuming worst-case delay times, a full speed device at the bottom of 5 hubs and cables has a timeout margin of 280ps. Reducing this margin to 0ps would only give you an extra 5cm, which is hardly worth the trouble.

**zeke_mo** · November 19th, 2007

Originally Posted by zazal

My backup device is a USB 2.0 250 MB Iomega Hard Drive.I'd like to put
it in my garage, requiring about 20 to 25 feet of wire. The official
USB specs say 5 meters max; if further use a hub/repeater.

I'm wondering how realistic the 5 meter spec is. I recall that parallel
printer cables were supposed to be limited to 10 feet or so; 75 foot
cables worked just fine. Same thing with the specs for RS-232 cables.

Does anyone have any real world experience with long USB 2.0 cables?
I'm thinking of building mine using unshielded CAT5 cable, one twisted
pair for power, another for data. Wise? foolish?

250MB? Might be time to upgrade

**gonaads** · November 19th, 2007

Don't push the limit when it comes to cable length specs. These are set so you don't get data corruption. It's better to use a hub/repeater and be totally safe especially if you data is important.

Now my curiosity is getting the better of me. Why do you want to put the backup drive in your garage so far away? External drives are small and take up little room/space. Why not have it close by?

**Shamus MacNoob** · November 19th, 2007

Just add another hard drive to the machine they cost nothing now.

**Tuffgong4** · November 20th, 2007

is it a temperature thing??? do you want the hard drive to stay cool?

either way when it's data or even sensitive data the shorter the cable the better.

Also if you've just purchased the backup drive see if you can buy an external hard drive with networking instead, (NAS)

**LeeJend** · November 20th, 2007

You don't put computer equipment in a garage, regardless of cable length. Heat, cold, humidity, dust, roaches, ants and other vermin crawling around inside of it will trash the device.

**X-Istence** · November 20th, 2007

Originally Posted by LeeJend

You don't put computer equipment in a garage, regardless of cable length. Heat, cold, humidity, dust, roaches, ants and other vermin crawling around inside of it will trash the device.

I absolutely agree. I used to have a machine I kept downstairs in the basement, and when I finally had to move it with me to Arizona, I took the case apart after it having been online for a good year and a half and it was FILLED with dust. I was surprised the fans even kept moving in that thing (good thing they did :P).

Took a good hour to vacuum it out, and get all the dust out of the heatsink.

**Shamus MacNoob** · November 20th, 2007

Another one post wonder who will not come back to thank us?

**Bman** · November 20th, 2007

Originally Posted by zeke_mo

250MB? Might be time to upgrade

Yea, MB? was that correct, thats not that usefull as a backup.

**Heeter** · November 21st, 2007

Hmmm,

I have a printer on a custom made 50 foot USB cable. It's no HD, but I haven't had any problems with it. Maybe printers are easier on data transfer than Hd's.

Heeter

November 19th, 2007	Top \| #1
zazal OSNN One Post Wonder Joined: November 2007 Posts: 1 Reputation: 10 Power: 0	USB 2 Maximum Cable Length My backup device is a USB 2.0 250 MB Iomega Hard Drive.I'd like to put it in my garage, requiring about 20 to 25 feet of wire. The official USB specs say 5 meters max; if further use a hub/repeater. I'm wondering how realistic the 5 meter spec is. I recall that parallel printer cables were supposed to be limited to 10 feet or so; 75 foot cables worked just fine. Same thing with the specs for RS-232 cables. Does anyone have any real world experience with long USB 2.0 cables? I'm thinking of building mine using unshielded CAT5 cable, one twisted pair for power, another for data. Wise? foolish?

November 19th, 2007	Top \| #2
fitz *XPista7eopardix Joined: April 2004 Location: Chicagoland Posts: 4,028 Reputation: 2947 Power: 168**	Re: USB 2 Maximum Cable Length personally, I wouldn't do it. As it's your backup device, would you want to risk data loss and/or data corruption caused by signal degradation onto a backup device? A printer is one thing to try to stretch the distance limit.. a Hard drive and backup data is entirely different. Go buy a USB hub, put it somewhere in between and get two 5m cables. http://www.usb.org/developers/usbfaq/#cab1 1. Why are there cable length limits, and what are they? A: The cable length was limited by a cable delay spec of 26ns to allow for reflections to settle at the transmitter before the next bit was sent. Since USB uses source termination and voltage-mode drivers, this has to be the case, otherwise reflections can pile up and blow the driver. This does not mean the line voltage has fully settled by the end of the bit; with worst-case undertermination. However, there's been enough damping by the end of the bit that the reflection amplitude has been reduced to manageable levels. The low speed cable length was limited to 18ns to keep transmission line effects from impacting low speed signals. 2. I want to build a cable longer than 5 meters, why won't this work? A: Even if you violated the spec, it literally wouldn't get you very far. Assuming worst-case delay times, a full speed device at the bottom of 5 hubs and cables has a timeout margin of 280ps. Reducing this margin to 0ps would only give you an extra 5cm, which is hardly worth the trouble. Hee-hee! Evil makes my buttocks tingle.

November 19th, 2007	Top \| #3
zeke_mo (value not set) Joined: August 2004 Location: Placerville, CA Posts: 1,965 Reputation: 1290 Power: 126	Re: USB 2 Maximum Cable Length Originally Posted by zazal My backup device is a USB 2.0 250 MB Iomega Hard Drive.I'd like to put it in my garage, requiring about 20 to 25 feet of wire. The official USB specs say 5 meters max; if further use a hub/repeater. I'm wondering how realistic the 5 meter spec is. I recall that parallel printer cables were supposed to be limited to 10 feet or so; 75 foot cables worked just fine. Same thing with the specs for RS-232 cables. Does anyone have any real world experience with long USB 2.0 cables? I'm thinking of building mine using unshielded CAT5 cable, one twisted pair for power, another for data. Wise? foolish? 250MB? Might be time to upgrade "My Mind is a swirling miasma of scintillating thoughts and turgid ideas" ~Sam Zeitgeist Money as Debt, educate yourself.

November 19th, 2007	Top \| #4
gonaads Beware the G-Man Joined: March 2002 Location: XP-erience, NTFS, OSNN, Bay Area, California Posts: 18,474 Reputation: 4070 Power: 348	Re: USB 2 Maximum Cable Length Don't push the limit when it comes to cable length specs. These are set so you don't get data corruption. It's better to use a hub/repeater and be totally safe especially if you data is important. Now my curiosity is getting the better of me. Why do you want to put the backup drive in your garage so far away? External drives are small and take up little room/space. Why not have it close by? *"I play violent video games, I could snap at any second."*

November 19th, 2007	Top \| #5
Shamus MacNoob OSNN Veteran Addict Joined: January 2002 Location: Brossard,Quebec Posts: 4,199 Blog Entries: 1 Reputation: 1481 Power: 182	Re: USB 2 Maximum Cable Length Just add another hard drive to the machine they cost nothing now. ASUS PN5-E SLI,Intel E8400,2 x 8800GTX 768mb SLI,ASUS VW266H 26 inch LCD, 8 GB Crucial Ballistix Tracer, Silverstone Strider 850watt PSU.Windows 7 Ultimate 64bit.

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November 20th, 2007	Top \| #6
Tuffgong4 The Donger Need Food!!!! Joined: June 2002 Location: Chicago Posts: 2,465 Reputation: 840 Power: 153	Re: USB 2 Maximum Cable Length is it a temperature thing??? do you want the hard drive to stay cool? either way when it's data or even sensitive data the shorter the cable the better. Also if you've just purchased the backup drive see if you can buy an external hard drive with networking instead, (NAS) Home Intel E6600 \ Abit AB9 Pro \ 4 gig Corsair DDR2-667 \ EVGA 9800GT \ HDD 1 320GB sata + 1 1.5TB sata \ 1 1TB backup drive / Samsung S183L SATA DVD-RW \ Windows 7 Pro x64 Laptop Asus UL30VT\ Intel CULV SU7300 \ 4GB Ram \ Intel Integrated + Nvidia 200m \ 500GB HDD \ 13.3 inch LED \ Windows 7 Premium x64

November 20th, 2007	Top \| #7
LeeJend OSNN Veteran Addict Joined: January 2003 Location: Fort Worth, TX Posts: 5,261 Reputation: 3386 Power: 199	Re: USB 2 Maximum Cable Length You don't put computer equipment in a garage, regardless of cable length. Heat, cold, humidity, dust, roaches, ants and other vermin crawling around inside of it will trash the device. Thought for the new millenium: In a world without walls and fences, who needs Windows and Gates? - Open Office - Firefox - Thunderbird - Gimp -Ubuntu - Red Hat -

November 20th, 2007	Top \| #8
X-Istence * Joined: December 2001 Location: USA Posts: 6,496 Reputation: 2808 Power: 220	Re: USB 2 Maximum Cable Length Originally Posted by LeeJend You don't put computer equipment in a garage, regardless of cable length. Heat, cold, humidity, dust, roaches, ants and other vermin crawling around inside of it will trash the device. I absolutely agree. I used to have a machine I kept downstairs in the basement, and when I finally had to move it with me to Arizona, I took the case apart after it having been online for a good year and a half and it was FILLED with dust. I was surprised the fans even kept moving in that thing (good thing they did :P). Took a good hour to vacuum it out, and get all the dust out of the heatsink. An engineers technical notebook

November 20th, 2007	Top \| #9
Shamus MacNoob OSNN Veteran Addict Joined: January 2002 Location: Brossard,Quebec Posts: 4,199 Blog Entries: 1 Reputation: 1481 Power: 182	Re: USB 2 Maximum Cable Length Another one post wonder who will not come back to thank us? ASUS PN5-E SLI,Intel E8400,2 x 8800GTX 768mb SLI,ASUS VW266H 26 inch LCD, 8 GB Crucial Ballistix Tracer, Silverstone Strider 850watt PSU.Windows 7 Ultimate 64bit.

November 20th, 2007	Top \| #10
Bman OSNN Designer Joined: July 2002 Location: Ottawa, Ontario Posts: 8,722 Blog Entries: 106 Reputation: 1386 Power: 221	Re: USB 2 Maximum Cable Length Originally Posted by zeke_mo 250MB? Might be time to upgrade Yea, MB? was that correct, thats not that usefull as a backup.

November 21st, 2007	Top \| #11
Heeter Overclocked Like A Mother Joined: July 2002 Location: In front of my computer Posts: 2,729 Reputation: 684 Power: 154	Re: USB 2 Maximum Cable Length Hmmm, I have a printer on a custom made 50 foot USB cable. It's no HD, but I haven't had any problems with it. Maybe printers are easier on data transfer than Hd's. Heeter

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