Windows Search, Google Desktop, Copernic - there are plenty of PC search tools around, and they all work in a similar way. An indexing engine crawls over every part of your hard drive, indexing all the words in each of your documents so you can find them later. It's a lengthy process that can tie up system resources, and is prone to error (if the index becomes corrupted then searches will no longer work).
Everything takes a different approach. The authors know that NTFS drives already maintain a list of the files they contain (it's in the MFT, or Master File Table), and so they use this to build their index. There's no crawler, no resource-hogging word-by-word indexing, the entire process takes just a few seconds.
And searching is even better. We tried looking for particular document names on an almost full 750GB drive with almost 430,000 files, and in every case it gave us the details just as soon as we'd finished typing them. This really is instant searching.
There are a couple of down sides. Everything only works with NTFS-based drives, so you can't use it to search most USB drives, or anything else with a FAT file system. And it only indexes file names, not their contents. Still, even if you keep your existing desktop search system, it's worth installing Everything as well just for its extra performance in tracking down lost files.