Seagate's Replica drives are designed to do one thing and do it simply: back up your entire Windows PC. They literally make a replica of your system, operating system and all.
The Replica comes in two configurations. The entry-level $130 250GB Replica is geared to single PC backup, while the $200 500GB version comes with a dock and is capable of backing up multiple PCs. (The dock is just a plastic housing that mounts the drive vertically; it still needs to be connected to PCs one at a time while backing up.)
The drive itself is fairly compact, measuring 5.61 inches high by 3.99 inches wide by 0.72 inch deep and weighing 0.57 pound. For whatever reason, the supplied USB cable is unusually short, but you can replace it with any standard mini-USB cable. The cable hardwired to the dock, meanwhile, is a two-headed model. That lets it get the proper amount of power from some laptop ports, but it also means that it might require you to sacrifice two ports rather than one.
We put the multi-PC Replica through its paces in our labs, pairing it with the HP Touchsmart TX2z laptop. The initial backup takes a while--a little over 2 hours in our tests--and if you have a PC loaded up with lots of files, it will take even longer. (To be clear, the Replica is not for Macs, which have their own built-in Time Machine software for backing up your system to a standard, Mac-formatted external hard drive.)
However, after you do the initial full-image backup, the Replica backs up your PC incrementally as files are added, deleted, or altered. You can leave the Replica connected to your machine or disconnect it and then plug it in when you're ready for another backup. If you're attempting to back up multiple PCs, the drive predetermines whether you have room to back up the second PC and won't start the backup process unless you do.