Verifiable backup

Please define a ?reliable verifiable backup??

Often I have observed warnings about editing the registry. With the suggestion of first obtaining a verifiable backup. How does one know that the backup will actually work? IE, the motherboard goes and an upgraded motherboard is required. Or the entire Mirror goes out, (ok it’s not likely) and it impossible to purchase the same disks.

Are backup to tape with verification as one of the options really reliable?

Does the backup from one machine to another online disk always work?

Thanks for your advice in advance.

preuter