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I want to buy a Pen Drive and a HDD. For both case I get two categories. USB2.0 and USB 3.0.

I wish to ask my T.V. is compatible with USB 2.0 pen drive. I wish to buy USB 3.0 pen drive. But that is much costlier than USB 2.0. also please let me know If USB 3.0 Pen drive is compatible with USB 2.0 ?

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2 Answers 2

  1. USB 2.0 has a max speed of 480mbps while USB 3.0 has a max speed of 4.8gbps (Roughly 1 gbps = 1000 mbps).
  2. USB 3.0 devices are Green Devices, meaning they use less power and are more efficient/stable.
  3. USB 3.0 devices are capable of communicating their latency speeds to their host for better transfer speeds.
  4. USB 3.0 devices leave eSATA and Bluetooth technologies far behind, and are the next generation devices.

USB 3.0 devices will work on USB 2.0 ports, but getting a USB 3.0 compatible machine or host is far more expensive than getting a USB 3.0 device. Ideally you should be buying a 3.0 device, buy if you aren't planning to run it on a 3.0 compatible host, you might as well get a 2.0 device. Another [cheaper] option includes buying a PCI-E x1 card with USB 3.0, which run fairly cheap (I've seen one for $10 with a molex connector). Then you only get enough ports for what you need.

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Add-on to the above points. Using usb 3.0 device on usb 2.0 port would give faster read/write speed than what you get on usb 2.0 device and port. So I prefer you to get usb 3.0 as its the future technology. –  Vimal Venugopalan Aug 23 '12 at 10:07
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@VimalVenugopalan - Using a USB 3.0 device on a USB 2.0 port would limited the USB 3.0 device to USB 2.0 speeds. It would act like any other USB 2.0 device MOST USB 3.0 cables are backwards compaitable. The speed of a USB 3.0 device on a USB 2.0 would give you the same speeds as a USB 2.0 device. –  Ramhound Aug 23 '12 at 11:42

You can use a USB 3 device in a USB 2 socket, but it will be limited to USB 2 speeds.

USB 3 is much faster (10x) than USB 2, it has the same 4 pins as USB 2 and a set of extra pins for USB 3, but in the same physical form factor (the plugs are the same)

You can use a USB 2 device in a USB 3 socket, and vice versa quite happily. But you'll be speed limited in both scenarios.

Additionally, the USB 2 spec dictates that a single device cannot draw more than 500ma, for USB 3 this is increased to 900ma. For self-powered devices or very small devices like pendrives this isn't a issue - but is a significant benefit for larger devices like external hard drives, or for charging other devices.

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There is more to consider besides speed. USB 3 devices may be designed to use up to 900mA of power whereas USB 2 ports will only offer up 500mA. If the device is asking for more than the port can offer, the device will not work without external power. With pendrives, it isn't as big a deal as they shouldn't even come close to 500mA, but given the question about the differences between both USB revisions, this should be documented for others who arrive here with similar questions about different USB 3 devices. –  MaQleod Aug 23 '12 at 9:38
    
Noted. I've added those details to my answer. –  PhonicUK Aug 23 '12 at 9:50
    
USB3 is a pure copper cable solution. AFAIR fiber optic lines were only considered at the beginning of the standardization. –  Robert Aug 23 '12 at 9:55

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