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The different terms used for backups can sometimes make the process seem more difficult than it is. I clarify some backup terminology and help sort it out.

Leo, Don't you think you neglect incremental backups as being as important, if not more important, than system backups? One of the questions that I submitted in the past two weeks had to do with how you use a backup from one system if the machine dies and you purchase another brand. Wouldn't incremental backups be more important than a system backup if system backups would be useless with a brand new computer?

In this excerpt from Answercast #8, I discuss the various types of backups, when and how you should use each strategy, and give my recommendation.

Incremental backups are important

I think there's a little confusion. First of all, I certainly don't neglect incremental backups. I think that they are a critical part of anyone's backup strategy.

A system backup and an incremental backup are two terms that actually don't relate.

You have:

  • Full backups with incremental backups and

  • System backups versus data backups.

So, I want to talk a little bit about what those terms really mean - at least the way that I use them.

One of the problems with some of these terms of course is that there is not necessarily a generally accepted definition. Sometimes, people will use them and mean something slightly different.

A system image backup

From my perspective, a full backup (or a what I often refer to as a system image backup) is a backup of every bit of data that's on your hard disc.

That includes Windows; it includes the boot sector; it includes all of your installed programs; it includes all of your data.

A data backup

A data backup backs up only the data files on your computer.

What to backup?

Now, the question is: what's a data file? Well, that's where things get sticky because many programs that perform only data file backups make some assumptions. For example, they might assume that you put all of your documents in My Documents.

Well, that's not where I put my documents. I put them all over the place and I want all of that other stuff to be backed up. But fundamentally, the data backup is just that; it backs up some definition of what it thinks of as your data files - or some subset of the files that are on your computer.

It makes sense that those kind of backups exist because not only are they faster and smaller, those are the kinds of backups that work well if you're doing something online (if you're backing up to an online backup service).

Backing up your entire system (doing a system image) online is impractical. Typically, the system image is huge, big, compared to the speed at which you can upload data.

Data backups, on the other hand (backups of just the data files), are useful in a case like that because no matter what (you could lose your entire computer), but you still have the files that you care about; the data files that you care about.

You could reinstall Windows; you can reinstall your programs, but there's no way to recover your data unless you actually have your data backed up somewhere.

System or data?

So, when I talk about system or image backups, I mean your entire computer, entire hard disc.

When I talk about data backups, I'm talking about just the data files on your system.

Full vs. incremental

Now, a full versus an incremental backup. The confusion is probably that an incremental backup typically starts as a full system backup; a full backup of your entire machine.

An incremental backup then says, "OK, I'm going to back up only what has changed since the previous incremental backup and if there wasn't an incremental backup previous, then from the previous full backup."

What that means is that:

  • On day one you do a full backup.
  • On day two, the backup includes only those things that changed during day two.
  • On day three, the backup includes only those things that changed during day three.
  • On day four, it includes only those things that changed during day four.

Now, I have not talked at all about the difference between data and system files. For a properly set-up backup, there is no relationship in this particular strategy. An incremental backup will back up whatever has changed: be that your data files, be it the registry, be it a new program you installed - whatever.

That's one of the reasons that incremental backups are so important. They bring your system up to the time of when that backup, that incremental backup, was taken.

Incremental requires a previous full backup

The downside to an incremental backup is that in order to use it, you need the full backup that it's built on - plus all of the incremental backups in between the time you took that full backup and the time that you want to restore to.

So, for example, in that scenario that I just outlined: where we have a full backup on day one, an incremental on day two, [and] an incremental backup on day three. If we (for some reason) want to restore our machine to the condition it was in on day five, we need to have in our possession (for the backup program to use) the full backup from day one, the incremental backup from day two, the incremental backup from day three, four, and five. So it gets a little bit more complicated.

You could take full system backups every time if you wanted to, if you've got enough space and enough time to take the backup.

The nice thing about incremental backups is that they're typically smaller and faster because they're only backing up things that have changed.


So, I do think incremental backups are incredibly important to keep your backup up-to-date.

What I typically recommend is that you schedule your backup software to do a full system image backup once a month and then do incremental backups on top of that every night.

That worst-case scenario at the end of the month - if you need to restore the computer to the incremental backup of last night - you will need the initial full backup and all 30 or however many incremental backups. But that's the trade-off between incremental backups being so much faster and so much smaller.

Restoring to a new machine

Like I said, I think there's some confusion in the terminology and the question.

In this scenario that you sort-of outlined where you're trying to backup from one system to another, it doesn't really matter whether you're using the full backup or incremental backups. The problem is that this backup that you're starting from, that you're required to lay down first, is for a different machine.

To install a backup of any kind (including a system image backup) from one machine to another, you start running into problems with things like device drivers. The backup contains device drivers and settings for the computer that it was backed up from, which is not necessarily the same as the computer it's being installed onto. Therefore, Windows may not work.

An incremental backup on top of that is absolutely critical because as you point out, that's where your data files are going to be. So I don't see the two as being mutually exclusive. I do think that they're very complementary and I think that it's mostly about just a confusion in terminology.

Next - What's the difference between system restore discs and system repair discs?

Article C5196 - April 11, 2012 « »

Leo Leo A. Notenboom has been playing with computers since he was required to take a programming class in 1976. An 18 year career as a programmer at Microsoft soon followed. After "retiring" in 2001, Leo started Ask Leo! in 2003 as a place for answers to common computer and technical questions. More about Leo.

Not what you needed?

April 13, 2012 9:26 AM

Some backup programs offer a third alternative to full and incremental backups--differential backups. These are somewhat similar to incremental backups in that they depend on a previous full backup. But they are different in that they capture all changes made since that full backup and do not depend on anything else. Thus to restore to a given point you need just the full backup and the differential backup taken at that point. So restores can be made more quickly, but since each differential backup (except the first) has more in it than a corresponding incremental backup would, they take more space.

January 28, 2013 6:00 AM

So, bottom line, as you say in your last section, a full backup (system image) is completely useless when your computer is broken and you need to restore to a new machine.

Is there a way to make
1. a system backup of just Windows, the drivers, registry, etc. WITHOUT the data files, which would mean a smaller backup than a full backup (in my case I have huge data files),
2. make also a data backup of all your personal files (full and incremental) which could also be used to transfer files to a new computer when needed?

The problem seems to be that a system image cannot be selective (just the windows and driver files).

So my question is: Is there a way around that????
Would it be useful to make different partitions, one for Windows and drivers, and one for personal data files? Could I then backup the "Windows" partition as system image, and backup the "data" partition as a regular data backup (with increments)?

January 28, 2013 10:55 AM

Actually, system images from a good backup program ARE selective in the sense that you can use a recovery disk to pull out just your data files in the case of a crash. So it is not useless at all.

It's such a better way to go because some programs save data in their own directories on your computer... at least as default. And if you are trying to just select your data you might miss something. Besides, why bother with an image backup with incrementals does it all.

February 5, 2013 2:04 PM

Connie, you say you can be selective in "recovering" from a system image. But I was asking if you can be selective in "creating" a system image of just windows and driver files.

In my case, my hard disk is practically full (only 56 GB free out of 665 GB) (I'm doing video edition), which would mean a HUGE system image.

I would like to be able to make a relatively small system image of windows, programs and drivers, anc complement with a separate backup of my personal files with regular incremental backups.

Is that possible without creating partitions?

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