Re: [tlug] Possibility to recover a hard disk by swapping control board: USB Power Limits (Especially on Laptops)

[jep200404@example.com]

On Sat, 17 Sep 2011 01:33:09 +0900, Zev <zev@example.com> wrote:

> On Sep 16, 2011, at 11:17 PM, jep200404@example.com wrote:
> > Boot a live CD, such as but not limited to Knoppix, 
> > in a desktop computer (_not_ a laptop), ...

> Why not a laptop?

Because on a laptop, there is a greater chance that the USB 
port will not give as much power as your drive wants. 

USB devices say how much current they use, from 0 mA to 500 mA. 
USB hosts _must_ grant requests for <= 100 mA. 
However granting requests for > 100 mA is at the discretion of 
the host. Laptops are generally stingier with power, and have 
a significant chance of denying requests for > 100 mA. 
Even more so, when they are running on batteries. 
Shutting off a device that uses more power than was granted 
is fair game. Desktop PCs have plenty of power. 

Furthermore, the hard drive's USB interface is likely cheating. 
The dual plug thing is usually for sucking more power and 
even then, it's not following the USB specification. 
It is relying on the host not following the USB specification. 

You are more likely to succeed on desktop PCs. 

If your external drive enclosure has provision for external 
power, then you could use it with confidence with a laptop. 
Another way, is to use an external hub with some (non-standard) 
high power ports. Targus has some. 
   
   http://www.targus.com/us/productdetail.aspx?sku=acp50us
   http://www.targus.com/uk/product_details.asp?sku=ACP45EU