Today, full-system encryption in software is feasible and practical. Here's how to get up and running using solutions from PGP, McAfee, Sophos, and open-source options TrueCrypt and DiskCryptor. There was a time, not all that long ago, when a fully-encrypted system disk was something only for people with money to burn.
You bought a special disk controller which performed hardware-based encryption, and then trusted the hardware vendor to make sure everything was implemented properly -- e.g., that they were using a good algorithm, that the key size for the encryption wasn't laughably short, and so on.

Today, full-system encryption in software is both feasible and practical -- although how practical will depend on the workload involved. But it's not a security silver bullet, much as it might seem to be from the outside. It can, and does, add a layer of protection that greatly reduces the risk of data compromise in the event hardware is lost or stolen. But that protection depends entirely on how it's implemented, and whether or not the user's been educated in the way an encrypted system works.

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