Re: Swapping Drives - Sanity Check

[Pascal Hambourg <pascal@plouf.fr.eu.org>]

Le 23/02/2019 à 17:21, rhkramer@gmail.com a écrit :
> On Saturday, February 23, 2019 10:52:20 AM Pascal Hambourg wrote:
> > Le 23/02/2019 à 15:41, rhkramer@gmail.com a écrit :
> > > On Saturday, February 23, 2019 07:53:23 AM Pascal Hambourg wrote:
> > > > Le 23/02/2019 à 08:53, David Christensen a écrit :
> > > > > Understand that if you disconnect the power cable to a motherboard,
> > > > > drive, peripheral, etc., but not all the other cables (e.g. SATA
> > > > > cable), you can fry electronics.
> > > >
> > > > Right. This is why power pins are longer than data pins in hotplug
> > > > connectors, so that they are connected first and disconnected last.
> >
> > > Hmm, that surprises me -- I guess I would have expected that you want the
> > > data pins connected first (while no power is applied), and disconnected
> > > last (again, while no power is applied).
> >
> > Why would you want this ? From an electrical or logical point of view,
> > it makes no sense.
>
> Well, two reasons:
>
>     * in most cases (other than hot plug) you want to make connections first,
> before you turn on the power  (I mean, for example, you don't assemble your
> computer with the power on)

Most computer parts connections (CPU, RAM, PCI cards...) are not 
hotplug. For those which are (SATA in AHCI mode), you can connect them 
while the power is on, power cable first.

Besides, the point is not just about connecting the data pins but 
applying voltages to them while the device is not powered. If the whole 
computer is powered off, there is no voltage on data pins.

>     * and somewhat similarly (but in a very different context) in a 3 pin power
> plug for an ordinary household outlet (in the US), the ground pin is longer
> than the power pins so that the ground is connected before power is applied.

This is not similar at all. The ground pin is not a data pin and does 
not carry any voltage.