Re: USB hard disk speed?
- From: Russell May <russmay@xxxxxxxxxxxxxxxx>
- Date: Tue, 30 Aug 2005 23:44:12 -0500
On Wed, 31 Aug 2005 11:49:06 +1000, "Rod Speed" <rod_speed@xxxxxxxxx>
wrote:
>Folkert Rienstra <see_reply-to@xxxxxxxx> wrote:
>> "Russell May" <russmay@xxxxxxxxxxxxxxxx> wrote in message
>> news:q7f9h1h37t8mscsbap890u4kllkefdmhls@xxxxxxx
>>> On Tue, 30 Aug 2005 19:06:35 +0200, "Folkert Rienstra"
>>> <see_reply-to@xxxxxxxx> wrote:
>>>> "Peter" <peterfoxghost@xxxxxxxx> wrote in message
>>>> news:%c_Qe.4946$2F1.298099@xxxxxxxxxxxxxxxxxxxxx
>>>>>> Copy times and rates:
<snip>
>>> I knew that USB 2.0 is limited to less than its maximum data rate of
>>
>>> 60MB/sec,
>
>> What 60MB/s ,
>
>60MBytes/s cretin.
>
>> it's 480Mbit/sec.
>
>> 480MBit/s is 480Mbit/s . Not 60MB/s and not 48MB/s either.
>> It's the clock rate converted to bits. There are 10 bits for each byte
>
>Wrong.
You guys got me interested, so I looked it up.
See http://www.usb.org/developers/docs/usb_20_02212005.zip
usb_20.pdf sections 5.4.1, 5.6.3, 5.8.3, 7.1.9, 11.3 for examples.
Data is listed as 8-bit bytes. Maximum bandwidth is listed as 60MB/sec
for high-speed isochronous transfers. Bit stuffing (insertion of a
zero after a sequence of six ones) is data dependent and multiplies
packet time by up to 7/6, adding an average of up to 4/3 bit time per
8-bit byte.
>> and then there is other overhead for serial protocol and then there is the
>> usual overhead for commands. Apparently there is about 1/3 overhead
>> on the converted to bytes number (serial protocol + command overhead).
>
.
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