Helping people with computers... one answer at a time.
Backing up is, of course, incredibly important. Knowing what to backup, where to backup and how often to backup are just as important.
I purchased backup software and even after reading the online documentation I don't understand what files I should be choosing to back up. And will I burn these to a disc or put them on my hard drive? I have the PC's installation files so I know I don't really need these, but I am so confused.
Good for you for even getting this far. So many people don't bother to backup at all and end up regretting it later when the inevitable disaster happens.
There are several answers to both of your questions and which to choose depends on what you have, your level of expertise, and how much effort you want to put into understanding and configuring your backup. And as always, there are tradeoffs.
I'll start by outlining what I do since it's a combination of paranoid safety, as well as relative simplicity - even for me.
I happen to use Macrium Reflect, with the following configuration:
It backs up to my 3 terabyte NAS.
I back up everything on my C: drive, which is the only other drive on this system. And by everything I mean C:\ and everything within it: operating system, programs, and data.
I use the Macrium scheduler to perform a full backup once a month, where an image of everything is copied.
I use the scheduler again to perform a incremental backup every night. This backs up only everything that's changed since the previous incremental or full backup.
That's it. With that everything is backed up every night. Should I lose something, even the entire hard disk, I can recover from the previous day's backup.
Now, let's look at those decisions I made, and how you might or might not make different ones.
Where to Backup
To start with, you should never backup to the same hard drive that you're backing up. The major point of a backup is to be able to recover from a hard disk failure. If your backups are on the same disk that just failed ... well, putting it technically, you're screwed.
The next best, in my opinion, is an external hard drive, such as I'm using. There are several reasons: it's always there and ready, purchase a large enough one and chances are it'll hold your entire backup, and it's portable - should your machine die, you can just move your external hard drive to another and recover your data.
Backing up to another machine (using Windows File Sharing) is also a very reasonable approach, though it will probably be slower than a directly connected device.
After that it becomes a matter of convenience. The remaining alternatives are typically smaller than the backup itself, it means you'll need to physically swap out media as it fills up. For example DVD-R's are probably the next most useful, since they hold the most (4.7gig), but you may find yourself having to purchase and manage swapping in blank DVDs as the backup proceeds. CDs and even floppies are possible, but since they're smaller, things can quickly become a hassle.
What to Backup
There are two basic directions you can choose when deciding what to back up:
If you don't know exactly what should and should not be backed up, then backup everything. The entire drive, as I have done. There are other advantages for this, as we'll see in a moment.
If you do know exactly what should be backed up, you know what you are doing and you have a strategy for recovering your system after a catastrophe, then by all means, backup only what you know you need.
The problem is that it's extremely difficult to know what to backup. Programs place data files and settings and all sorts of random things in random places on the hard disk.
A backup of everything will allow you fairly quickly restore everything. By that I mean when things go bad, you may be able to restore your entire system - operating system, programs and data - in one restore operation.
A backup of only what you think you need means that when a restore happens, you'll need to reinstall the operating system, reinstall the applications, reconfigure the applications to your preferences, and then recover your data from backups. A much longer and error prone path. I can almost guarantee you that at least one file you'll wish you had backed up will have disappeared forever.
You can guess which way I'm leaning: backup everything, it's safer.
The Exception: if all you have to backup to is small media (say CDs, though perhaps even DVDs may be too unwieldy for a full backup for you), then you may need to make some hard choices. Backup "c:\documents and settings" and everything in it for a start, and then look at where on your hard disk your programs are storing your data. Backup those folders as well. And then be prepared for a long recovery process should you ever experience a failure.
How Often to Backup
This should really be a function of only one thing: how heavily do you use your computer.
If, like me, it's your primary business and source of income, then nightly backups are a must. There's no question. Even if you don't have a disaster, the ability to recover a file you had yesterday but accidentally deleted today can be a huge time saver alone.
If you are just a casual user then your needs may be different. One way to gauge your needs is simple: think carefully about what you do on your computer, perhaps monitor yourself for a week. Now, consider if you suddenly lost a week's worth of activity - all pictures, email, documents, whatever. Everything that happened in a week, gone. Does that hurt? Then you need to backup more frequently than that. If you don't care, then perhaps less frequently might be ok.
Now, I said it should be a function of only your usage. However I do want to throw two other factors into the decision making process:
Importance: You may not use your computer heavily, but when you do use it it's extremely important. In this case you may need to elect for more frequent backups to preserve that important information.
Convenience: The practical reality is that if your backup involves swapping DVDs in order to make it happen, you're probably not going to do it as often as you should. Shoot for more frequently than you need, so that you actually do it often enough.
And, of course, particularly if important and convenient are at odds with each other, you may very well want to consider purchasing better backup media - like that external hard drive - so that you can automate the backup process, or at least make it as easy as possible.
Regardless of how you do it, where you do it, and to a less extent how often you do it, the most important thing is simply that you do it. Given the incredibly large amounts of information that we rely on our computers to retain for us, backing up has never been more important.