The Registry is a large database that holds thousands of important settings for both Windows and your installed applications. Every time you use your PC, new settings are created, while others are modified or deleted, and this activity soon leaves gaps that waste hard drive space and consume a little RAM.
Quicksys RegDefrag can fix this problem, though, by analysing your Registry, then compacting it to remove any wasted space (that's wasted space only - the program does't look for or delete any broken Registry entries). We tried it on a test PC, and after a 5 minute scan, it reported that our Registry was 181,792KB in size, but 12% of this was wasted space. We clicked the Defragment button, and moments later the job was done: our Registry was now 21,972KB smaller.
While that sounds impressive, it doesn't actually mean we'll save almost 22MB of RAM. Windows never loads the entire Registry into memory, so our actual savings will be a small fraction of the RegDefrag figure, probably not enough to make a measureable difference to most PCs. Still, the program will save a few resources, and if you're looking to squeeze the maximum performance from your system then this might be worth a try.
Be wary, though - as with all Registry tools, a software bug or hardware crash mid-defragment can cause serious problems, that may prevent your PC booting normally next time. Only use RegDefrag if you have System Restore turned on, a Windows installation disc or bootable recovery disc to hand, and feel confident you can get your system working again if something goes wrong.