...A computer that is sitting completely unplugged from everything around it, will not be as affected by an EMP as your microwave plugged into the outlet. Same goes for an electronic lock on a safe. It wouldn't be bothered by an EMP either. ...
Most people fail to realize that EMP strikes happen every day. The sun gives off a lot of these pulses that effect the earth. Cell phones don't work as well, Over-the-Air TV doesn't come in clearly, or CB radios won't reach as far.The atmosphere absorbs most of it, but even a nuke detonated within our atmosphere wouldn't affect EVERY SINGLE electronic around. ....
We should all review, in detail, the literature that's out there. Sure, if you are 2,000 miles from an event you'll be OK unplugged, 1,000 miles, not so much. Your equipment doesn't have to be plugged into the power grid to be damaged....the pulse amplified by the Compton effect in the upper atmosphere will enhance the reaction and actually generate a current within a discreet component (even if it's on the shelf for a replacement somewhere, like for your car computer). The EMP events referred to as a daily occurrence are orders of magnitude (an order of magnitude is a log scale measurement where, starting as low as, for example, 0.01, then next is 0.1, then 1.0 then 10, then 1000, then 10,000, then 100,000 then 1,000,000 and so on...) greater than the day to day occurences we see.
Sometimes the natural events are responsible for power outages in Canada and they've designed for it....but an EMP event will be much stronger than a natural event. In fact, a solar event in the mid 1800's took out telegraph service in the US, much more robust a system than our cell towers, computers, power grid, car computers, industrial equipment, etc. of today. The solar events generally are tied to power lines to generate the current...and EMP event is different in it's characteristics and far more severe than anything we've seen from a solar event.
Unplugging won't help if you are "near" an EMP event....that's one of the things that is so catastrophic about it. Your battery in your car will be OK...your ignition system will be fried. Good thing is, EMP is basically line-of-sight and it does have a limit to it's extent, so it would take several to knock out the entire US.
Again, read the literature that's out there and attempt to discount what internet experts have to say. There are some declassified Mil-spec documents on how to measure and protect from EMP that can help and, if you've a bit of electronics savvy, you can read them for yourself and assess the level of damage that can be experienced from an EMP event. Also take a look at how an underground power grid was taken out in Russia during some nuclear tests...the severity caught everyone offguard and reinforced that EMP effects can find their way into Faraday cages built for the protection of systems that does not have proper protection for ingoing and outgoing lines.