There might be multiple causes for system slowness and instability, but one of the most common ones is disk fragmentation. It forces your hard disk to overwork, noticeably increasing the time it requires to read a file, specially big ones. Fortunately, there are specialized tools like Smart Defrag by iObit, which you can use for free to overcome that problem.
The program offers you a dark colored, ultra-modern user interface which gives you easy access to all the available functions. They are organized into tabs, being the first one "Disk Defrag". There you can analyze and defragment entire disks or drives, specific files and folders and/or optimize Windows apps. This section offers you a predefined set of optimization functions you can execute by simply clicking on the button labeled as "Smart Defrag", "Optimize" or "Smart Optimize", depending on your selection. However, you can also select the specific task you want to execute among "Analyze", "Fast Defrag", "Defrag & Optimize", "Large Files Defrag", "Free Space Defrag" and "Defrag & Prioritize Files" options.
The second tab is "Boot Time Defrag" and it provides you with one of the program's most powerful features - programming an automatic defragmentation process for those files that cannot be relocated while Windows is running. They include the paging file, the hibernation files, the Master File Table (MFT) and other system files. This feature, of course, can be easily turned on or off. The third tab is "Game Optimize" and it is specifically designed for gamers. They can select one or more game files (e.g. executable files) for optimization, so they can take their gaming experience to the limit.
Finally, there is a fourth tab labeled as "Action Center", but it is mostly advertising and provides you with some shortcuts to other utilities published by iObit. Besides of all the manual functions mentioned before, Smart Defrag also monitors your system from the background, without interfering with your daily activities. The program automatically detects when a file requires defragmentation and warns you through a popup window that shows on the notification area, so you can take the appropriate actions. And of course, this feature can also be enabled or disabled through the program's settings window.
All in all, Smart Defrag is a powerful system utility that, in my opinion, is worth trying. It allows you to keep your system free of disk fragmentation and running at optimal speeds, almost automatically. To top it all off, you can use the program free of charge, though some of its functions are unavailable until you register it, like automatic defragmentation.