Is a backup an alternative to having no Windows installation CDs?

First, let me say "good for you" for having a backup solution,
regardless of what solution you chose. That already puts you ahead of
the game compared to most other computer users.

A full initial backup is an excellent safety net and can cover for
not having installation CDs in many cases. However, from the way I
worded that you can probably guess that there may be issues, but the
good news is that they're rare.

Let's review the best way to use a full backup in a case like
this.

To refresh your memory, a full backup of a computer makes a copy of
every file on your hard disk. And I do mean every file. It
backs up Windows, all your programs, all your data ... everything.

To use a full backup as a pseudo replacement for your installation
CDs, the moment you get your brand new machine you install your backup
software and you make a full backup right then, before you've
done anything else. This gives you a "snapshot" of your machine on the
day it was brand new.

If you find yourself needing to "reformat and reinstall", without
having the installation media, you could instead restore this
particular backup image with similar effect.

Let's touch on a couple of issues to make sure your initial backup
is complete:

• The full backup should happen as soon as possible after having
  received the new machine. As I said before, this creates a snapshot of
  the machine as clean as possible, before anything but Windows and the
  backup software was installed. Before even connecting to the network,
  if at all possible.

• It needs to be a full or "image" backup. This is critical.
  Regardless of what backup program you use, the backup needs to be such
  that it can be restored back to "bare metal" - your machine with an
  empty hard disk.

• Since the restoration will have to happen to "bare metal", make sure
  that your backup program provides a boot disk or other bootable
  solution. With an empty hard disk you'll have no operating system to
  boot into - the backup's restoration program will have to provide that.
  Quite often this means that as part of taking that first backup you
  should also take that opportunity to burn a restore or rescue disk
  provided by the backup program.

• It needs to be of all partitions that came with the machine. This is
  easily overlooked. Many machines now place recovery information on a
  second partition - sometimes a second drive, "D:", or sometimes hidden.
  Most backup programs will backup a drive, and you'll need to specify
  which drives; be sure to specify or backup all partitions.

Now you'll note that I indicated you should take this first backup
prior to even connecting to the network. Some will argue that you
should first connect up and take all the Windows Updates and patches
that you can, as you'll then have a more up to date image should you
ever need it.

I say do both if you can, but do what I suggest if you can only do
one.

The problem is simple: you've connected to the network for that
update. In the worst possible scenario that could expose you to
malware. If you get infected, and then take a full backup, the backup
itself will be infected. The whole point of this exercise is to cover
for not having installation CDs, which themselves have not had Windows
Update run on them, and come virus free. Focus on that first.

Taking and saving additional backup snapshots later - like after
Windows Update has been run, or after you've installed all your major
applications - also makes sense if you have the space to keep the
backup images. But if you have only enough space for one, make it the
first one.

And as an aside, if you're reading this hours, days or months after
having set up your machine so that initial pristine state of your
machine is long gone, that's ok, but take a backup snapshot as soon as
you can. Having a known good full backup to revert to, even if it's of
a well used machine, can still go a long way towards acting as a safety
net if something goes wrong later. That's the whole point of backing
up, after all.

The biggest limitation with this approach is simply that restoring a
backup isn't the same as running Windows Setup. That means that if the
hardware on your machine has changed significantly since you took that
backup, you may have troubles when you restore it. How much trouble
and what kind of trouble will depend entirely on your specific machine,
what changes were made, and whether or not the manufacturer included
all the appropriate drivers and other software somewhere on that
initial image.

But having an initial full backup of your machine can compensate for
not having installation CDs in many, many cases. If you find yourself
in this situation, I recommend that you take a full backup as soon as
possible.