When it comes to backing up a computer, what most people think of, copying files, is somewhat limited. Copying data files is fine, as far as it goes, but a running computer also consists of applications.
Under Windows, the concept of backing up an application doesn't exist.
When the subject comes up at all, the context is usually to retain a copy of the CD the software came on, or the original downloaded file that it was installed from. The goal being to enable a re-installation of the application, not to back it up in its current state.
Re-installing is sub-optimal. Your favorite web browser, for example, would lose all its bookmarks, plug-ins, saved passwords, GUI customizations and everything else that makes it yours.
The design of Windows is such that installing an application typically places files all over the place, not to mention updating the big, complex behemoth that is the registry. This approach makes it impossible to backup an application, as its footprint is like that of an octopus. Even software designed to un-install an application, can't find all the tentacles of the octopus - un-installing Windows applications frequently leaves traces behind.
Portable applications are very different, but here too, the common mindset works against us.
They are typically thought of in terms of running off a USB flash drive (thumb drive, pen drive, etc. ). Well and good, but to me, the real benefit of portable applications is that you can back them up. Backing up applications is great Defensive Computing.
By design, a portable application exists in a single folder. All the tentacles of its octopus are lassoed in one place. Copy the folder and you have a backup of the application, including your customizations.
Disk image backups do backup applications, but that's not really why they exist. Their purpose is to backup everything, which is overkill if you're only interested in backing up a small number of applications. Plus, they are much more complicated compared to the simple act of copying a folder.
You can get started with portable applications at www.portableapps.com, a great collection of free Windows software that is ever growing. Among the recent additions is a portable version of Google's Chrome web browser. I highly recommend the site.
Portable applications also benefit from avoiding the Windows registry.
Bugs in the application can't screw up the registry and, in turn, the application can't be impacted by problems with the registry. Then too, just decreasing activity in the registry is probably a good thing.
The whole concept of the operating system and applications sharing a data store just rubs me, and others, the wrong way. Especially a data store that is not reliably backed up (System Restore is flaky).
Another upside to avoiding the registry is that it lets you run multiple versions of the same application without having to resort to virtualization.
Interested in trying out the latest beta of Firefox version 3.6? You can download a portable copy of it from portableapps.com and run it on a Windows computer with a normally installed copy of Firefox. The only restriction is that the portable copy of Firefox can not run concurrently with the normally installed copy.
I use this trick all the time to kick the tires on new Firefox extensions in a test copy of Firefox before moving them over to my production copy of Firefox.
Uninstalling portable applications is a simple matter of deleting a folder, they shouldn't leave behind any remnants.
Not only is this neater, it also offers privacy. In fact, privacy is what drives some people to portable applications.
When run off a USB flash drive, a portable application shouldn't leave any traces on the host copy of Windows. Someone interested in untraceable web browsing might opt to run a browser off a USB flash drive.
My experience has been that running applications off a USB flash drive is noticeably slower than running them off an internal spinning-platter hard drive. So, although I use portable applications all the time, they reside on, and run off, a hard drive.
One downside is that many, if not most, Windows applications are unavailable in portable editions. However, some applications may, in fact, be portable even though they are not advertised as such.
If you haven't used portable applications, I encourage you to give them a try. Even if you don't like them, they are unlikely to cause any problems.
And, they run off a thumb drive.