USB 2 speed

  the hick 16:30 31 Jul 10

I am backing-up HP 6735s data to seperate Iomega hard-drive. The speed is displayed as 7.0 MB/sec., and is taking some while, about 26GB of files to copy. This seems a bit slow, although it's some while since I backed-up large amounts of data. I do not think this is usual, any comment please?

  Fruit Bat /\0/\ 16:48 31 Jul 10

Without going into any technical detail, USB is broken up into three speed groups;
Low Speed USB1(1.5Mbps), Full Speed USB1.1 (12Mbps), and Hi-Speed USB2 (480Mbps)

  the hick 16:52 31 Jul 10

Fruit Bat /\0/\, thanks for this info., must be a fault with mine, it's less than USB 1.1. Shall investigate later.

  Fruit Bat /\0/\ 17:23 31 Jul 10

check you have an Enhanced driver listed in your USB in device manager.

  SirMetal 20:22 31 Jul 10

480Mbps means 60MB's a second, not 480MB's a second. USB 1.1's 12Mbps = 1.5MB's a second. So all in all, you are running USB2, it just isn't used at it's full speed when transferring smaller files.

  DieSse 21:04 31 Jul 10

"The speed is displayed as 7.0 MB/sec"

To explain more what SirMetal says above -

B = Bytes

b = bits

So 1MBps = 8Mbps and your

7MBps = 56Mbps

Older (IDE) hard drives can only run at a long-term (ie not instantaneously from their cache) read rate of 30-40MBps - which is less than USB2. Added to that writing is much slower. And writing involves some reading too, and USB2 only works one way at a time. And small files add lots of overhead writing file system data in between writing the data files. And that if the drive is fragmented, there is lots of (much slower) head movements in between writing blocks. And if the drive is older and doesn't use some of the optimization techniques. Then the whole process is much slower than you might think.

  woodchip 21:38 31 Jul 10

As above do not confuse Meg Bits with Bites

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