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FAQ : USB in general
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 USB in general
Contents    
FAQ-ID = usbspec-nnnn
0001: USB specification
0002: USB data transfer ability
usbspec
-0001
 USB specification
Q1 May we have questions about USB 2.0 specification ?
A1 For question about USB 2.0 specification, please refer the document which is released from the web below,
USB 2.0 Specification (USB Implementers Forum)
Q2 What is the difference between USB 1.1 and USB 2.0 specification ?
A2 The latest specification of USB is version 2.0. USB 1.1 specification defined Full-Speed (12Mbps : FS) and Low-Speed (1.5Mbps : LS) whereas USB 2.0 specification added Hi-Speed (480Mbps : HS) operation to USB 1.1 definition. In general,

USB 1.1 only supports LS/FS modes ; USB 2.0 supports LS/FS/HS mode.
When indicating the data transfer rate, the representation: 'FS', 'LS' or 'HS' could be used.
(2004/12)
usbspec
-0002
 USB data transfer ability
Q1 How fast data can be transferred by using USB 2.0 ?
A1 Specified speed of USB 2.0 is 480Mbps(i.e. 60 MB/s), but 60MB/s is NOT the actual data rate.
This is because USB 2.0 packet is inclusive of overhead data.

Moreover, idle time are added between packets.
Besides, data rate is also dependent on the system architecture, the PCI bus and the attached USB devices.

Therefore, actual data transfer rate will be lower than 60MB/s.
Our measurement result of data transfer rate with USB 2.0 storage device (HDD) is about 20 - 25MB/s on average.
(2004/12)

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