On 15/04/2011 15:14, Herbert Graf wrote:
> On Fri, 2011-04-15 at 09:57 +0100, Michael Watterson wrote:
>> On 15/04/2011 09:17, Xiaofan Chen wrote:
>>> On the other hand, even though I have bought two
>>> USB 3.0 external hard disks, none of my PCs
>>> come with USB 3.0 host controller (XHCI)
>> For Random Access, an HD might just beat USB 1.1
>>
>> Only bursts to or from the on-board controller cache can exhaust the
>> speed of USB 2.0 on a single drive.
>>
>> Drives are natively faster toward edge of platter. Native block transfer
>> sequential speed (excluding track to track stepping or random access) is
>> limited by rotational speed and bit density. For larger transfers, even
>> without Random Access, the track to track delay is very high.
>>
>> USB 2 is worthwhile. I'm sceptical that USB 3.0 is needed for ordinary
>> single drives.
> I'm not sure why you say that.
>
> Pretty much ANY modern drive will EASILY saturate a USB2 connection. The
> fastest most people can transfer over USB2.0 is about 30MBps, it's been
> a while since a hard drive was that slow.
>
> I regularly transfer many GBs of data over a USB2 connection (an
> external USB harddrive for offsite backups), I can't wait for USB3 to be
> more common.
>
> TTYL
>
>

Me neither, could you explain this?
Although seek times are pretty slow, the average sustained disk to=20
buffer rate for a 7200 rpm desktop drive according to the Wiki page is=20
around 1030 Mbits/s, so around 100MB/s. This will be higher for more=20
advanced drives, e.g  10,000rpm.
http://en.wikipedia.org/wiki/Hard_disk_drive
I definitely notice a slower transfer rate when using my external USB=20
2.0 drive, compared to internal transfer.

--=20
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