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Re: hot plugs

On Fri, Feb 05, 1999 at 11:25:37AM -0800, Mark Ayzenshteyn put this into my mailbox:

> Hi all,
> 
> I weird thing happened to me on the way to the forum. 
> 
> I was plugging a printer into a printer port of my print server(486 with
> linux 2.0.33) This thing is an old packard bell with a riser card. It has
> 2 parallel ports, 1 built in & 1 on a separate isa card. So I was pluging
> a printer into the port on the iSA card and the sytem was on and running.
> I guess I pressed a little to hard and the isa card came out of its slot
> while the box was on. I thought it was curtains for the system and the
> card, but I saw no sparks so I turned it of, took it apart and replugged
> the card back in. THen I plugged the printer back in and it works. Now I
> didn't know ISA was a hot bus. So why didn't something fry?

Well, since it sounds like you just dislodged the card, and didn't try
to plug it back in while it was on, you're probably OK. Stuff doesn't
just fry randomly; you have to send a certain amount of power to the
wrong lead or port for that to happen, or cause a surge (i.e.,
change the current draw on the power supply such that it compensates,
and ends up sending more power than can be easily dissipated to a certain
component.)

About the worst that probably would have happened - assuming you didn't
try to reseat the card - would be that the software/cpu/whatever tried
to access something on the card, couldn't deal with the fact that it
wasn't there, and froze.

I think a lot of the "fear of frying" is instilled into people by
hardware manufacturers; Apple used to warn people against plugging
and unplugging ADB cables while the Mac was on - "or the ADB chip will
fry and you'll have to buy a new motherboard!". As it turns out, the
cases when the ADB chip fried occurred when dumb people forced the
plug in incorrectly, and ended up sending the +5v signal up the
data lead (or something similar). Not easy to do, but where there's
a moron, there's a cup holder.

Note: don't take this as carte blanche to go around unplugging
your cables while your systems are on }:> But if it happens accidentally,
don't worry too much about it. And Mark: that screw notch and hole for
attaching an ISA/PCI card securely to the case is there for a reason. }:>

-dalvenjah

-- 
 Dalvenjah FoxFire (aka Sven Nielsen) "We've lost the bleeps, the creeps,
 Founder, the DALnet IRC Network       and the sweeps!" "That's not all
                                       he's lost!"
 
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