why can't we get full speed from any interface?

Muneeb Ahsan

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Oct 22, 2010
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USB 2.0 supposed to provide 60 MByte/sec transfer speed but it only provides only 30-35 Mbyte/sec same goes for SATAIII and usb 3.0, can any one please explain why we can't get full speed, whats the factor behind it.?
 

popatim

Titan
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Its your understanding that seems to be needing updating.
These things work at the lowest common denominator; ie - the slowest device in the chain. With USB3 its often the device being used. Attaching a 100mb/s external hdd to 600mb/s usb3 port won't magically make the drive work faster, sorry.
Then there's protocol overhead to account for. This is why you won't see 60mb/s from usb2 or 600mb/s from usb3 or 600mb/s from sata3, and so on. Look at pcie3. It has twice the bandwidth of pcie2 but they did not double the clock rate or the number of lanes. they increased the clock rate 60% (from 5ghz to 8ghz) and protocol improvements generate the rest.
 

Muneeb Ahsan

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Oct 22, 2010
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i very well understand what you are saying, but still i havn't got my answer yet. If i plug usb 2.0 in usb 2.0 port why can't i get 60MB/sec data transfer speed which it intended to provide (480mb/sec) same goes for USB 3.0. I know , if i put usb 2.0 in usb 3.0 port we wont get usb 3.0 speed "magically", but what happened when i plug usb 3.0 in USB 3.0 port but still we dont get the intended speed (600MB/sec or 5Gb/sec)? i really appreciate if someone give me the complete explained answer. Thanks