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November 26, 2010

Safe Nap Habits Your Hard Drive Will Thank You For

Written by Jeff Sobel

 

I often see people doing something relatively dangerous to their laptops, so thought it worth writing a blog post about.  Maybe it will save someone from having to take advantage of Apple’s amazing AppleCare and restoring all their files from their Time Machine backup.

One of the great things about MacBooks is that they wake from sleep almost instantly when you lift their lid.  This is because when the computer is in Sleep mode it retains all the data in its memory (RAM) by using a small amount of power.  Since the contents of its memory are saved, when the computer wakes up it comes back in exactly the same state as when you put it to sleep.  Since power is required to retain the information in the computer’s RAM you’ll notice that if you leave your MacBook unplugged in sleep mode for awhile it will have less available battery when you wake it back up.  That’s the price you pay for the instantaneous wakeup that we all love.

So what happens when the battery is completely drained?  Well, when the MacBook senses that the battery is just about depleted it goes into a deeper sleep mode, commonly referred to as Hibernation.  In Hibernate, the contents of the RAM are written to the hard drive and the computer goes completely to sleep.  Because hard drives don’t require power to retain their data, Hibernate mode doesn’t use the battery.  But when the computer is woken back up the RAM must be restored by reading from the hard drive, which takes several seconds.  Most people have experienced this, it’s what’s happening when you wake your MacBook and see the pale screen with the white progress bars.  The more RAM you have, the more time this will take.

Now here’s where the dangerous habits come in to play.  Because Sleep mode requires power it’s entirely possible that a MacBook left closed and unplugged could deplete its battery while asleep.  Apple engineers know this, of course, so they designed the computers to write the RAM to the hard drive BEFORE going to sleep each time you close your MacBook’s lid or manually initiate Sleep mode.  That way if the battery runs out while the computer is asleep, the MacBook will automatically enter Hibernate mode and all your hard work will be intact when you wake it back up.  This is great.  The problem is that it takes several seconds to write the RAM to the hard drive when you put the computer to sleep.  And what I see almost every day in coffee shops and classrooms is people slapping the lid of their MacBook closed and then immediately dropping the laptop into their backpack.  Sometimes they do this gently.  Oftentimes they don’t.  They figure the computer is asleep so what harm could a little jostling do to it?

We all know that hard drives are a bit delicate.  When their laptops are on, people are generally very careful not to drop them or throw them around.  But when the laptop is asleep, or when people think it’s asleep, the rules seem to slacken a bit.  You tend to assume that if the computer is shut down that it’s safe to drop it into a backpack or hastily put it up on a table in a far more crude way than you ever would if it were on.  But since the MacBook takes several seconds, sometimes up to 30 seconds if you have 4gb or more RAM, to store the RAM to the hard drive, it is still very much on when so often it is snatched up and dropped into a bag or tucked under an arm.  And that’s bad.  Particularly because that’s a time that it’s guaranteed to be writing data to the hard drive, which is when hard drives are their most vulnerable.  A little drop could cause the drive’s head to bounce on the platter, corrupting your data and potentially causing physical failure of the drive.

So get in the habit of being gentle with your MacBook just after it goes to sleep.  And when possible, wait until it’s fully asleep before throwing it into your bag like a frisbee golf disc.  It just might make the difference between a happy Mac and a Sad Mac.

Sidenote:  I’ve had people tell me, “But Macs have the Sudden Motion Sensor that’s supposed to park the hard drive’s heads when it detects it’s being dropped or jolted so I shouldn’t have to worry about bashing my MacBook around like a piñata.”  Sure, the SMS is pretty cool, and it might save you from having a hard drive that prefers not to do anything but make little whirr-click sounds after a fall, but you’re much better off thinking of the SMS in the same way you think about the airbags in your car: they’re a great added safety measure, but having them doesn’t mean you should drive your car into a wall.

Also, there are free utilities that will allow you to customize your MacBook’s Sleep and Hibernate parameters.  I use one to prevent the writing of RAM to disk when I know I won’t need Hibernate mode, or to force the Mac into Hibernate mode when I want to maximize battery life (when traveling in places I won’t be able to recharge or on long flights, for example). 

Next entry: Keeping Up With The Bus... There's an App for that!

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