Computer hardware question (technical)

[pharoah0110]

I've been working with PC's for well over twenty years now, and this same question still boggles my mind after all this time.
Many years ago, a friend of mine was installing a ISA card on his P1 (like I said a Looong time ago...), and in the rush of things he forgot to power-off the system before installing the card in the slot.
...you can imagine what happened...
We both saw the spark, and the Mobo was dead after that, as well as the graphics card that was already installed.
Obviously, he had to replace the destroyed hardware. Of course, there are now mobos out there now that allow hot-swapping of ide devices and peripherals (mostly in servers), but I was wondering what exactly plugging-in or unplugging an ISA, PCI, or PCIE peripheral with the power "on" does to destroy the IC's and components on a mobo.

Forgive me if it's a stupid question, but I was discussing this with someone today, and I still can't figure out why it happens this way.

Any takers?

Cheers!!

 

[tblaxland]

Given the design of ISA cards, it is entirely possible that if the card was not aligned properly, adjacent pins in the socket were shorted out by the contacts on the edge of the card. Depending on the circuits connected to the socket, this could voltages and/or currents to be present in parts of the motherboard where they were never designed to be. For example, shorting an open collector output to +5V could easily be fatal for an IC (have a look at the circuit diagram and you can see there would be very little impedence in the circuit to limit the current below the tolerance of the IC. The same thing is possible to achieve with PCI/AGP cards (I can't comment on PCIe since I don't own any of those, either sockets or cards ). Inadvertant shorting of pins is more difficult to do on IDE/ATA/SATA/SCSI/etc type connectors which makes them more suitable for hot-swapping.

Aside from the shorting issue, even if you did manage to get a PCI card inserted whilst powered up, there is a good chance that it will not work and possibly crash the BIOS also, since the bus protocols are not designed to expect new devices whilst in operation. It is possible to do however, with the right hardware: http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1003,C1006,C1140,P32052

EDIT: BTW, how do you "forget" to power down the PC? Isn't the whirring of the PSU fan a little distracting?

 

[pharoah0110]

IIRC, he was in a hurry, and the tower itself was horizontal on the floor, with the monitor facing the other way. It was too long ago to remember the exact circumstances, but I agree it was a stupid mistake...LOL.

On the subject of hot-swappable devices, it the technology more expensive? They seem to be able to accomplish it quite seamlessly with USB.

Cheers, and thanx for the reply.

 

[tblaxland]

On the subject of hot-swappable devices, it the technology more expensive? They seem to be able to accomplish it quite seamlessly with USB.

The electronics cost is marginal, IMHO, but the connectors would definitely be more expensive, especially for a large multipin connector capable of withstanding the sort of torque and vibration that a PCI connector can hold. The other option would be non-rigid connections but that would involve adding mounting hardware and additional space for the connectors/cable.

 

[TSPenguin]

USB was specificaly designed to be hot swappable, as nearly every other external connector on a PC (with the famous exception for PS/2) has been designed with hot swapping in mind. SATA for instance is a mainstream connector that does support hot swapping of traditionaly internal devices.

Accomplishing hot swapping with slot cards and RAM is unlike more different because of the way BUSes work and adresses are assigned. Mainboards that support this usaly need extra hardware to control the slots and specificaly designed BIOS software and controlers. Of course the operating system needs to be able to cope with hot swapping these devices too.
AFAIK hot swapping slot cards and RAM has always been a dirty hack for consumer products.

 

[cjp]

One thing USB is designed to do is to first let the ground connector make contact, before the more sensitive signal connectors are connected. This should provide a safe way of discharging any electrostatic differences between the two sides.

 

[Notebook]

I think a general rule is, if it needs a tool to remove, replace, or install, then switching off the equipment is a good idea. If its on the outside and can be done by hand, then its probably been designed to be safe...

Of course it dosen't protect against somebody putting a circuit board in upside down because the manufacturer hasn't used a keying pcb connector. Wasn't me, I was just watching; quite impressive, and expensive.

N.