6 and 1/2 Dozen, 1 reads faster and other writes faster in real use.
I have no idea why USB2.0 limits about 30MB/Sec when 480Mbps sec is far higher.
Read on Everything USB.
" USB 2.0 has a raw data rate at 480Mbps, and it is rated 40 times faster than its predecessor interface, USB 1.1, which tops at 12Mbps
But here is catch :
" As far as we know, effective rate reaches at 40MBps or 320Mbps for bulk transfer on a USB 2.0 hard drive with no one else is sharing the bus. Flash Drives seem to be catching up too with the some hitting 30MB/s milestone. For all we know, USB interface could become become the bottleneck for flash drives as early as 2008. "
Seems accurate, I only hit 30MB/Sec approx on my WD My Book but connect it by ESATA I hit 70MB/Sec.