Dan's Data letters #102
Publication date: 3 May 2004.Last modified 03-Dec-2011.
Sayonara, data
I was just browsing the Internet and the PC locked up.
Then I heard a dreaded clunk from the HD, and the PC won't boot any more.
Obviously there's data on there that I would like to be able to recover. Are these businesses that offer data recovery any good, or is it generally a scam (because they seem to charge a high premium for trying to recover the data)?
Dave
Answer:
Dead drive? What a shame. Well, just whip out your latest regular backup, and...
Sorry, but I can never resist saying that at times like this.
DVD burners and discs for them are darn cheap these days; they're an adequate backup solution for most small office and home users. If you've got scores of gigabytes of media files to back up, a whole other hard drive in a USB/FireWire box will do the trick; not bulletproof, but pretty darn unlikely to drop dead at the exact same time your main drive does, particularly if you keep the backup drive far away from the computer.
Some data recovery businesses certainly are on the level, but don't ask me which ones; I'd be inclined to try the ones that offer a free quote service first, but that's not exactly The Sage Advice Of The Century.
Generally speaking, you will indeed pay through the nose to get data recovered from a drive with a mechanical problem, because they're probably going to have to transplant its platters to a new drive of the same model, which takes longer than just swapping in a new circuit board to replace a borked one.
Which is not to say that they wouldn't charge you the same high amount for just a circuit board swap, of course :-).
In a pinch, it's possible to do a board swap yourself (although the clunk you heard may mean it'd be futile in your particular case)
First, you need a controller board that matches the borked one. Just buying another identical drive will probably get you a compatible board, but if some firmware version shuffling's happened then the new board might not like the physical layout of the old platters, or something. And, to repeat, if the problem's not on the circuit board, you're on a hiding to nowhere.
But if none of these problems apply, you just unscrew the boards from the bottom of each drive (you'll probably need a Torx driver, but an Allen key will do for Torx screws in a pinch), then screw the donor drive's board onto the dead drive. Basic anti-static precautions are a good idea, though lots of people get away with doing such tasks on an old newspaper on the kitchen table. You certainly don't need a ghetto cleanroom (a.k.a. a large clear plastic bag) to keep dust out of the drive while you do the deed; the boards aren't plugging any holes into the drive interior.
These days, all of the board-to-mechanism contacts will probably just be springy bits of copper pressing against pads on the underside of the drive chassis, so you won't even have to unplug any connectors.
I speak with the confidence of the man who's never had to do it, though. I've removed a fair few boards from drives in the course of converting them into fridge magnets and wall decorations, but I've never had to do a transplant myself.
Thanks, my friend, to backups.
Any part will do
Me and my friend at work here were just playing around with some notebooks and noticed that the touchpad does not work when you use a pen or other instrument, but only works with a part of your body (i.e. a finger).
How do the touchpads actually work? Do they work on heat, or moisture?
Tamara
Answer:
They use capacitance. If you try to fake out the touchpad with something electrically conductive, it ought to work.
There's more info on Synaptics' site here.
Laptop 'lectrocution
just read some reader responses on The Register discussing whether dropping a laptop into the bathtub would be dangerous to the tub's other residents.
So - is it dangerous? Or, that is, more or less dangerous than dropping the proverbial hair dryer into the tub?
Moritz
Answer:
The piece you linked to followed on from this one,
and these earlier letters, by the way.
No, it's not dangerous to drop a laptop running from battery power in your bath.
You might be able to give yourself a bit of a thrill if you sat in a plastic bath full of salty water with a big electrode on one side of you connected to the positive terminal of a laptop battery, and a similarly large electrode on the other side connected to the negative terminal; that'd allow your body to conduct a decent amount of the current, and if the breakdown of current flow was such that you got several milliamps through pretty much any of your tissue, it'd be quite uncomfortable (as I've explored before).
A setup like this might even be able to stop your heart, though it takes about 30mA before there's a real chance of that happening, and if the current path is through water it'll be distributed through your body enough that it may be surprisingly hard to get 30mA-plus through the cardiac region (another thing I've talked about before).
If you drop a laptop in the bath, though, even if the water's highly conductive (which it probably won't be), the only place the current's going to be going is from one part of the laptop to another. It's a battery powered device with no reference to mains earth, so no matter how well earthed the tub is or isn't, practically no current will have any reason to flow outside the laptop casing.
The same goes for peripherals hanging off the laptop, as long as they're powered from it, or from batteries of their own.
If the laptop or any peripherals are plugged into a mains adapter, things can be riskier, depending on the kind of adapter it is.
If the adapter's isolated, then it's still safe; isolation means there is, again, no direct connection to the mains, and the device might as well still be running from battery power.
If the adapter isn't isolated, though, then its output earth conductor is connected to mains ground, and that'd give current from the immersed device a reason to flow outside the casing to anything earthed in the bath - maybe the whole bath, maybe just the plug-hole, maybe nothing if the bath's plumbed with plastic piping and the cold tap isn't electrically connected to the water.
This is only likely to be a real danger if you're the only path to ground the current has, though. Even if the archetypal plastic-bodied unearthed hair dryer falls into a nicely earthed bath with you, allowing current to flow from active inside the device to neutral inside the device and ground via a nice earthed plughole (assuming you don't have a safety switch that'll cut off the power pretty much immediately when it sees current going from the active wire to somewhere other than neutral), most of the current will actually flow through the small path of water inside the device to its own neutral-connected components, rather than through the larger and thus higher resistance path of water (and human) outside the device to earth.
How, then, can you reliably kill yourself in a bath with a hair dryer?
Drop it in when it's plugged in, then lift it out again while you sit in the bath. Now, the wet hair dryer is held in your wet hand, most of the water will have fallen straight out of it as you lifted it, and so the current path to neutral inside it will be more difficult, and the current path to the bathtub earth through your body will look more attractive to J. Random Electron. Far less total current will be flowing once the thing's out of the bath, but your share of what is still flowing may well be enough to zot you.
Then you'll probably drop the gadget back into the bath, of course, and a naive observer of the gruesome scene later on could easily assume you died the moment the thing fell in, rather than taking a hand in your own demise.
Getting back to laptops, though - even if there's an un-isolated AC adapter and you do the abovementioned lifting-it-out thing while you sit in the water, the low voltages involved mean you're likely to be OK. LCD screen backlights run from at least several hundred volts AC, but backlight inverters have minuscule current capacity - below 10mA. You probably couldn't kill yourself with one even if you stabbed needles into your chest and hooked it up to them, unless the needles actually touched the heart. In that case, a mere tenth of a milliamp has a fighting chance of putting you into fibrillation; for this reason, medical procedures involving the heart and metal instruments need stringent stray-voltage control.
Getting back to the matter at hand, though - all of the rest of the laptop is low enough voltage to be no more risky than the abovementioned two-big-electrodes situation.
(If you've got a laptop with an internal power supply that takes mains power directly, of course, then it'll behave like any other mains appliance if dunked.)
Placebo power
Referring to your reply regarding V-Power fuel [in this column], I'm confused. I warn you that I have only a very basic knowledge of engines, mainly gleaned from How Stuff Works.
My understanding is that 98 RON fuel has more energy in it than 91 RON fuel (aside from it also being able to withstand higher heat/pressure before combusting). This would mean that the same amount of fuel in a cylinder would provide more power when combusted. If the car was incapable of providing enough air to fully combust the fuel (which would be detected by the catalytic converter), the amount of fuel would be reduced, giving the same amount of power, but more kilometres per litre.
Where have I got it wrong? Does 98 RON fuel not have more energy?
Daryl
Answer:
No, it doesn't. Octane rating just tells you the fuel's knock resistance. The higher
compression ratio this allows is what
makes more power; the fuel has no more energy in it, and without more compression (which
improves thermal efficiency), will deliver no more power.
All other things being equal, you should run your car on the lowest octane fuel its engine's rated for.
If you've got a choice between fancy expensive high-octane fuel and low-octane fuel that's loaded up with ethanol and impurities, the fancy fuel is a better choice, just because it's cleaner. But if that doesn't apply, buy the minimum your engine's happy with.
(Some modern engines can alter their ignition timing to allow them to run, but not as well, on fuel with a lower octane rating than they'd like it to have. If you've got a car that does this, then obviously the higher-octane fuel is once again probably what you want. Most cars don't work like this, though.)
Find some further reading on this subject here and here.
Plastic purchasing
I live in Australia (Brisbane), and I can't seem to find sheets of acrylic, besides in a hardware store for ridiculous prices. I was wondering if you had an idea of what type of stores to look in.
I'm just looking for some stuff as cheap as possible no more than 60cm square. I'm planning on using it for attaching a couple of case fans onto.
Thermal
Answer:
Try dedicated plastics suppliers. You want a place like Mulford Plastics.
Here's their Page O' Acrylic; they have a
Brisbane office, too, so they look like a good place
to start.
The sheet size you want is likely to be ridiculously small by their standards, but you should be able to get a sheet that'll give you plenty of spare space for mistakes, yet still fit in your car, for a non-silly price.
Since I put this page up, readers have suggested going to a plastic-sign fabricator or similar heavy acrylic user and asking for offcuts. Or you can try the Reverse Garbage lucky dip (that's their Sydney site; they have one in Brisbane too, though!).
Glazing shops are apparently also a good bet.
But wait - there's more! Click here to go to page 2 of this letters column!
