Types of Backup Software : What’s the difference between Disk Imaging, File Based Backup, or Synchronization, and which should I use?


Anyone who begins  looking into the various different backup technologies available today, will soon discover that not all backup software is created equal.  The three most commonly encountered technologies are Disk Imaging,  File Based Data Backup, and File Synchronization. Many people are confused about the differences between these, and rightly so because the software employing these technologies often overlap somewhat in function. 

I remember someone saying to me once, “Well, backup is backup. Right?  It doesn’t matter how you do it, as long as you do.”  It is true that doing some sort of backup is better than doing none at all, but there good reasons why different backup methods exist.  No one type is meant to be a complete replacement for the other.  I believe the different technologies complement rather than compete with one another.  In the paragraphs below we will be looking at each of the major types of backup software, what their primary purposes are, and their advantages.


Quick Index



Disk Imaging

This type of backup is often described as a “bare metal backup” because it backs up physical disks at the volume level.  In other words, a true disk image is an exact copy of an entire physical disk or disk partition.

In its simplest form a disk imaging program creates a bit identical copy of a drive which is made by dumping raw data byte by byte, sector by sector from the given disk into an image file.  Early disk imaging programs and image formats had a lot of limitations.  Because they copied the raw blocks of data from the disk “uninterpreted,”  even the unused area or white space was backed up too.  This led to very large image files even if the drives or partitions only contained a small amount of data.  Copying every sector of a disk in this way worked quite well for “disk cloning,”  where everything was being moved to a replacement drive, or was being multi-cast to several computer systems with identical hardware and configurations, but it was not really a very practical solution for regular backup of a system.

Fortunately, disk imaging technologies have been developed that eliminate many of the limitations faced by early adopters of the technology.  Most modern disk imaging programs have the ability to interpret the data being copied and remove or compress the empty blocks on a disk which leads to much smaller image files. The majority of programs also create compressed image formats that can be mounted and explored making it possible to retrieve individual files.  Also the creation of successive incremental1 or differential2 backups is often supported, which further reduces the demands on storage.  Other techniques have been developed that allow file-level operations such as file type filtering, such as the ability to exclude the large and non-essential pagefile.sys and hiberfil.sys from the image,  and the ability to image a drive or partition while it is currently in use.

New technologies aside, imaging programs generally still have the ability to do the “old-fashioned” low-level raw copies of a disk which has its advantages.  Full bit identical images retain deleted files or lost partitions that have not yet been over-written.  All file, file-system, and partition attributes are preserved. Bit identical images facilitate the ability to restore files and partitions to the exact same sectors as the originals.  This can prevent such problems as partition misalignment which can cause problems for certain operating systems.3  Since these tools can still handle un-decipherable raw data they can be used to backup any disk even if contains a foreign file system, an unknown operating system, or an encrypted partition. 

Advantages of Image Backup Systems

  • Allows for rapid full system restores including the operating system on the same or very similar hardware.
  • Speed and simplicity is unsurpassed when working with large numbers of files.
  • Many modern image formats can be mounted and used like any other drive making accessing backed up files very user friendly.
  • Performing image backups is generally much less resource intensive that file backups.

See also: Best Free Drive Cloning Software


File Based Data Backup

File based backup is the type of backup that most people are familiar with.  Because this form of backup has been around for so long, the technologies employed are quite numerous, and backup solutions have been developed for about every situation that can be imagined.  While only a few dozen different disk imaging programs are currently on the market, literally hundreds, pehaps thousands, of various file backup programs and systems exist. 

The simplest form of file based data backup is the basic copy of files from one location to another, but today’s backup programs do a lot more than just simply copying files. File backup programs are designed to automate the process of duplicating files in multiple locations and on numerous types of storage media, locally or across networks or even to remote severs such as online storage.   Most have the ability to add files to compressed volumes called archives and at the same time can apply encryption for added security.   After performing a full backup of selected data, most backup programs can perform cumulative backups of new or changed files.  Popular cumulative backup technologies are incremental1, differential2, delta style4, and binary patching5.  Some specialized file backup systems provide continuous (real-time) data protection (i.e., immediately backup up a file as soon as it is created), and others provide versioning systems that will make a new copy of a file each time it is changed. This allows the user to go back and retrieve a previous edition of the file. 

The power of file based backup lies in its flexibility.  Individuals who are new to backup software are often easily overwhelmed by more advanced programs because of the sheer number of functions and options that these tools may have.  Good file backup software can easily be set up to backup certain file types to specific locations using file include and exclude filters.  An example of this would be the ability to create a backup “job” that would copy only your digital pictures in .jpeg format to a specific external hard drive, and place them in folders by backup date.  At the same time another job could be setup to automatically backup all of your .doc files to online storage where they are safe and can be accessed from another computer. A third job could be configured to find all the files which are larger than a certain size and send them to a compressed archive while the originals are removed to free up space.

Advantages of File Base Data Backups

  • Fine control over every aspect of your backup routine.
  • Ability to work with small sets of files which is not usually possible with image backups.6
  • File fragmentation is greatly reduced if not nearly eliminated in backup archives.
  • Easier to restore full backups or migrate data to new or different hardware.
  • Generally more practical for remote backups over a network or Internet. (Note: Some new block level copy technologies are helping image based backups to gain some ground in this area as well)
  • Real-time backup or continuous data protection and versioning.
  • Deduplication technologies work better on file based systems.
  • Considered by many to be more resilient to error or corruption than imaging technologies.

See also: Best Free File-Based Backup Program


File Synchronization

File Synchronization (“file sync”) is really a specialized adaptation of file based backup technologies.  Some would even say it is not true backup, but the result is basically the same.  The primary design of sync programs are to replicate or mirror working files in two or more locations where both sets of files will still be put into service.  One way to understand the difference between synchronization and backup is that backup copies files in one direction while synchronization copies files (or changes) in two directions. In backup you have a “source” and a “destination.”  In true synchronization you really have two sources.   For example, when a group of files are set to be  synchronized between two computers, files which are changed on any one of the computers will be reflected on the other. 

Sync programs also differ from backup programs in that they generally provide detailed control over how file differences or collisions are handled.  Files that are renamed, moved or deleted in one location may be renamed, moved or deleted in the other based upon the users choice.  This is usually called the ability to “propagate” renames or deletions.  Often such programs keep track of files and file operations by creating a database. Among other things the database helps the program differentiate between newly created files and old files that only exist in one location, because they have been deleted in the other. 

Synchronization that replicates changes in both locations is called two-way synchronization.   Synchronization that only replicates the changes from one location to the second is called one-way synchronization. One-way sync differs from backup when propagate of deletions or renames is performed. Backups do not generally delete files, and a renamed file is usually copied again.

Some people use one-way sync as a way to both backup and synchronize computers.  A one-way sync may be made to a portable hard drive.  Basically the hard drive becomes a backup destination.  The hard drive may then be used as a source to sync with another computer and new files will be transferred from the portable drive to the pc.  New files on the second pc may also be backed up to the drive and later to be transferred to the first pc.  Thus both computers will remain in sync, and the data on the drive will remain as a backup of both.  Similar setups are often used by online storage services which may be looked at as being both online backup as well as online synchronization sources. While Sync programs may provide some sort of data encryption to securely transmit files between locations, they don’t provide compression and packing of files into archives like backup programs.

It is worth noting that many hybrid backup and sync programs that to a certain extent perform both file archiving and synchronization.

Advantages of File Synchronization

  • Improves productivity when working with the same set of files in different locations.
  • Files synchronized to online sources can often be easily accessed from any computer or mobile device such as a smart phone.
  • Some programs combine real-time sync with a versioning system that allows for easy collaboration between individuals working on the same file, and usually provide diff comparisons and merging capabilities.

See also: Best Free Folder Synchronization Utility


Article Notes

1. See: “Incremental Backups Explained,. “ for more information on this type of backup.
2. See: “Differential Backups Explained,” for more information on this type of backup.
3. Vista was sometimes left unbootable, some disks take a performance hit, and life span of certain solid state drives (SSD) may be shortened.
4. See: “Delta Backups Explained,”  for more information on this type of backup.
5. See: “Binary Patch Backups Explained,” for more information on this type of backup.
6. Some technologies exist to make an image of a single folder but they are not widely implemented.


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by CASD on 10. June 2014 - 4:48  (116702)

I want to put in a bigger hard drive, and I have a external hard drive I can save the first hard drive too..So that it can be loaded back onto the new bigger hard drive.. Would a use a backup program or ?

by Allen Steeves (not verified) on 26. October 2012 - 0:25  (101345)

Hey, after reading this, would I be correct in saying that by using an image back up I would be essentially creating a copy of my entire hard drive and in the event of say, for example, my drive crashing or whatever I would be able to restore my drive to the way it was, even if I had to get a completely new drive?

Apparently my hard disk is failing, my computer is nice enough to tell me ahead of time, and Im trying to back up my hard disk onto my 1 terabyte external hard drive (more than enough space). I would really just like to basically create a copy of my current disk which I can then just re-upload once I get this whole situation sorted out with as little hassle as possible. Is that even realistic?

by Ritho on 26. October 2012 - 6:36  (101358)

Yes you are basically right as long as the image is created correctly. But there are problems that can be encountered that will cause the restored image to be unbootable. Like a problem with the "Disk ID" or if you don't have a bootable rescue disk etc. If your current drive is still functioning then don't wait until it is dead to try to restore the image to the new drive.

Another option is using a software especially designed for bootable drive to drive cloning. I believe that Macrium Reflect which is mentioned in the drive imaging category on this site may have this capability now that it can make images of a running system. Another solid choice for doing this though would be http://www.runtime.org/shadow-copy.htm which is designed specially for this purpose.

Hope this helps!

by claraAnonymous (not verified) on 21. October 2012 - 21:00  (101155)

I am new to computers. I have been told of this program. I read your description of it. I feel somewhat comfortable with the explanation. I am downloading and grateful for the help. thanks sierra.

by Barry Hutchins (not verified) on 24. March 2012 - 17:48  (91075)

you mentioned the advantages of the different types of file/system back-ups but you gave no disadvantages to disk imaging compared to file sincronation and file based data backups. please give some examples so i can make an educated decision. thanks.

by uddhav (not verified) on 7. January 2012 - 4:08  (86738)

how many differace between two sectors

by Ritho on 7. January 2012 - 5:04  (86742)

Sorry, I don't really understand your question. Can you ask it with more detail?

by Ron D (not verified) on 5. November 2011 - 12:58  (82759)

Thanks for the info, but I'm kinda new in understanding about backup.. usually i just run a backup and cal it a day, but i want to be more tech savy and knowing about backup programs.. Whether free or paid, i would like to just have a great overall backup software... im looking for a program that as i make changes to files, it makes them as well, and i'm looking for a program that when it runs a backup, it only adds any new files or make changes to previous files without doing a whole backup of the hdd..(like if i add 1 file since my 1st backup, when i run it , it just add that 1 new file and thats it... and in case of hdd failure i would like to be about to restore my backup to a new add without a problem and continue where i had left off, without having to reinstall everything all over again :( ..Any help in pointing to a good software would be appreciated.. after reading the article im undestanding this a bit more now... how is [commercial software removed]? im seem to be getting mixed reviews on it... thanks for your help and God Bless you!

by Ritho on 5. November 2011 - 23:39  (82788)

Ron,please see http://www.techsupportalert.com/best-free-backup-program for my software recommendations. If you have any further questions please feel free to ask.

by R Collins (not verified) on 24. October 2011 - 1:10  (82020)

I have used "Sync Toy" by msft for years and been afraid of the syncro function. I now know that for my purposes, that fear was justified.

My data is largely my photo database and the echo function is great to copy the data from my primary drive to the four external hard drives but the sync function would have killed all my hours of Photoshop work if used.

Thank you for the readable and useful article.

by LE (not verified) on 9. September 2011 - 1:18  (79254)

I am still confused by the options. I used to have a LaCie drive that did my backups. I was able to verify the backups, and when I needed a file, I went to the drive and copied it back. I bought a new PC with 1Tb of storage, so now I have a WD drive and nothing is recognizable, I can't verify anything, and when I went to restore an Access database, the restore would not work.

Is this a new type of file formatting? Is the type of file backup I had with my LaCie drive still available for the now larger hard drives?

Thanks for any help.

by Ritho on 10. September 2011 - 13:42  (79370)

I assume that you used some backup software that came with your drive? I did a quick search on the net and found that LaCie provides a backup tool. Often backup tools use their own proprietary archive format, so you have to use the same software to open the files.

Hope that helps.

by Webmind (not verified) on 11. August 2011 - 20:16  (77496)

I agree with the above poster - great article.

However, one thing puzzles me. The writer states that traditional "file based" backups have the advantage of being "easier to restore full backups or migrate data to new or different hardware."

It would seem to me that "drive image" backups with the latest technologies mentioned would make restoring full backups or migrating date much easier (unless the hardware and/or operating system were significantly different).

Perhaps the writer could explain this a bit more clearly. Thanks.

by sharrukinu (not verified) on 9. March 2011 - 19:45  (67699)

I've been using "Gizmo's Freeware" for probably ten years -- since back when it was like "the 46 Best Freeware progs" (or similar; I can't remember the old name precisely). I've had countless occasions to be grateful for the resource, and that has only increased since it morphed into techsupportalert. But, I never really felt compelled to comment on anything. I've been a sys admin for about 16 years now, and this article on imaging, file backup, and synchronization is seriously one of the best, clearest, most succinct and accurate descriptions I've ever read. Even with decades of experience in IT, I still found distinguishing between these concepts to be difficult. Until I read this article. Thank you so much to the author for taking the time to think it through and write it up in a clear way. And thanks to techsupportalert for being here for us.


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