Time Machine Backup – Why you need it & how it works

Time Machine icon

Think about what information is on your hard disk, in particular think about the most important information on your hard disk. In my case it’s pretty easy – I have over 10 years of digital photo’s stored on my hard disk. These are irreplaceable photo’s of my two daughters growing up. One daughter has photos from when she was first-born all the way through to her current age. I would be devastated if anything happened to those photos.

Hard disks store digital information on flat circular disks called platters inside the drive. These platters are rigid and have a magnetic coating on both sides of the disk in which digital information is stored.

These platters are mounted on a spindle and spin at a rate of between 5,000 to 15,000 RPM.

The job of reading and writing data to the platters is performed by the read/write heads, that float on top of the platters on a super thin cushion of air that is only 3.7 millions of an inch thick

To put this in context a human hair is some 2000 millions of an inch thick.

If something goes wrong with the hard disk and the head comes into contact with the surface of the disk, the impact damage could make the disk unreadable.

It is not a question of if your hard disk fails, it is more a question of when it will fail.

Research done a few years ago on 100,000 Google hard drives, showed typical annual replacement rates of between 2% and 4% and up to 13% observed on some systems. Below is a chart that shows the approximate cumulative percentage chance of a hard disk failure over 5 Years.

Hard Disk Failure Chart


The research suggests that on average 30% of drives will fail before they reach the end of 5 years use. It is possible that a hard drive will last much longer than 5 years, but hopefully you can see that only storing data on your hard disk, puts that data at risk.

Between my primary Mac and my backup device I have 7 hard disks. My own experience in the last 5 years is three of those  disks failed and needed replacing. I would say that I have been slightly unfortunate, but it shows how important it is to have a backup system.

If you don’t have a backup system at the moment, I suggest you take a look at Time Machine, Apple’s built in backup solution that ships with OS X.

While there are other backup solutions available Time Machine has three major advantages.

  1. It is incredibly easy to set up
  2. Once you have it running you can almost forget about it, as it automates your backups.
  3. It is very easy to recover lost files.

Time Machine setup

Apple made setting up Time Machine as easy as possible. If you have a secondary internal hard drive in your Mac you can use that as your backup drive. However I suggest you get an external hard disk or an Apple Time Capsule. A Time Capsule is a fully featured Airport Extreme base station with large 2TB or 3TB hard disk, designed to work with Time Machine. Time Capsule might be attractive to laptop users as you are able to backup over WiFi. However if you have a desktop Mac, I suggest that you invest in an external backup drive.

To determine the size of the backup drive needed, I  suggest buying one that is 1.5 to 2 larger that your current hard disk in your Mac. So if you have a Mac with a 500GB drive get at least a 1TB external drive. External drives are pretty cheap these days and you should be able to pick up a decent 1TB drive for less than £100 ($130).

Depending on the ports on your Mac you can connect an external drive with Firewire, USB or even the new high speed Thunderbolt connector. However at this time Thunderbolt drives are pretty expensive and you don’t need a super quick drive for backup purposes. If your Mac has a Firewire connection I suggest you use that and get a compatible external drive, however USB2 is also fine for backup.

As soon as you connect a new external drive to your Mac, Time Machine will ask you if you want to use that as your external drive.

TimeMachine Start

Click “Use as Backup Disk” to confirm you want to use the drive for Time Machine backups.

On OS X Lion, check “Encrypt Backup Disk” if you want to encrypt the Time Machine backup external drive.

That’s all you have to do for Time Machine to automatically backup your Mac. Time Machine keeps hourly backups for the past 24 hours, daily backups for the past month, and weekly backups until your backup drive is full. When your Time Machine drive is full it will intelligently delete the oldest backups to make room for newer ones (and will alert you if the “Notify after old backups are deleted” option is selected in Time Machine preferences). This is why I suggest that you use a drive that is larger than your current hard disk. Even when your hard disk is full, Time machine will be able to hold a copy of all of your current files, plus keep some history of different versions of your documents as well.

The initial backup will take some time. I suggest you start your first Time Machine backup in the evening so that the initial backup is done overnight. You can continue to use your Mac while Time Machine backs up.

Once the initial backup is completed, Time Machine performs subsequent hourly backups of only the files that have changed on your Mac since the last backup (as long as your Mac is awake and the backup drive is connected).

Restoring from a Time Machine Backup

Restoring from Time Machine is simple. Select ‘Enter Time Machine’ from the Time Machine icon in your menu bar or click on the Time Machine icon in the dock. Time Machine appears to float the active Finder window above an astronomical background. Behind the current window is a ‘stack’ of older versions.

TimeMachine StarField

You can use the timeline on the right side of the window to reach a certain point back in time (the timeline shows the times of all backups on your backup drive). If you don’€™t know exactly when you deleted or changed a file, you can use the back arrow to ‘move back in time’.

You can also perform a Spotlight search in the Time Machine Finder Window search field to find a file. Type the search term in the Spotlight search field and use the back arrow to have Time Machine search through your backups to find what you are looking for.

Before you restore a file, you can also use Quick Look to preview the file. Select the file and press the Space Bar to bring up the Quick Look window.

To restore, select the file/folder and click the “Restore” button. The file will automatically be copied to the desktop or appropriate folder. If the file you are restoring has another file in the same location with the same name, you will be prompted to choose which file to keep or keep both.

In addition, some OS X applications can work directly with Time Machine to recover information. For example, if you select ‘Enter Time Machine’ while using Apple Mail, you can step back through deleted emails, in the same way as you can with files in the Finder.

Mail Time Machine

Other apps that also directly support Time Machine include Address Book, iPhoto (’08 and later) and GarageBand (’08 and later).

About a year ago my primary hard disk on my Mac failed and I used Time Machine to completely recover my system and files. If you’re restoring a whole drive, you need to use an installation disc. When reinstalling OS X on a hard drive, the installation process gives you the option to restore the whole drive using Time Machine. Select this option, connect the drive with your Time Machine backup on it (or select a Time Capsule volume) and let the software do the rest.


Time machine is not a complete backup solution because you might have the misfortune to lose both your Mac and your Time Machine backup to theft or disaster, but it’s a significant first step to protect you from human error, disk hardware or software failure. To me the great thing about Time Machine is it is so transparent, it just does its job quietly in the background until you need it. It’s reasonably inexpensive to buy an external drive, dead easy to set up and more importantly it does not rely on a human being to remember to change the backup tape!

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