Installing Smart Defrag Pro is relatively intrusive for a defrag tool, though it offers several options you don't always see available. You can defrag the registry files, which may somewhat rarely be of benefit, but you can do that with several other utilities too. You can defrag Windows page & hibernation files, but you can also just delete the page files after booting to something like a WinPE USB stick -- the hybernation file can usually just be deleted, or turn hibernation off -> on. Rewriting the files should create them in non-fragmented free disk space. You can also use a couple of free tools from Sysinternals -- docs.microsoft[.]com/en-us/sysinternals/ -- that can also defrag the MFT [Master File Table], which is another Smart Defrag Pro option. That said, it's debateable whether the MFT needs defragging... Smart Defrag Pro, a Sysinternals tool, and some [[I think mostly older] Paragon apps let you defrag the MFT, but by design it's located on a part of the disk that's reserved by Windows for the MFT and related files, so it shouldn't [in theory anyway] get that fragmented.
Smart Defrag Pro lets you schedule defragging, in fact adding several tasks to Windows Task Scheduler, like a Sysinternals tool lets you defrag individual apps &/or folders, and lets you run defrag in the background, only when the system's idle. One *I think* unique feature is to stop Windows VSS service when defragging to allegedly protect any system restore points that have been set.
Installation adds the programs folder, an IObit folder to Program Files / Program Files (x86), an IObit folder to ProgramData, plus files in ProgramData\ ProductData, with new folders added in C:|Users\ [UserName]\ AppData\ LocalLow & Roaming. A new driver's added, SmartDefragDriver.sys, that runs as a service [though it's not in the Control Panel -> Admin Tools -> Services applet], while IObitSmartDefragExtension.dll & SmartDefragBootTime.exe are added to Windows\ System32. I recorded 857 new registry entries in my Win7 32-bit VM, though I guesstimate about a third to 1/2 of those are meaningless cache entries.
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When data is written to a conventional hard disk, it's written as small chunks of data to the next available space on the disk platter(s). Windows writes to the hard disk somewhat constantly during operation, files are deleted, apps are uninstalled etc., so you wind up with blocks of free space in the middle of all that data. Defrag is kind of like Tetris, with remaining data taking the place of empty spaces where blocks were removed. It's also kind of a big deal after a full Win10 version upgrade [like 2004/20H1, but Not the coming 20H2], since once the old version is deleted, there can be a pretty big gap of newly freed space. [Note: some Windows -- & NTFS -- files cannot be moved. Win10's defrag *may* still move *some* of those immovable files.]
Since they're stored as small blocks of data, files can also become fragmented, for example when parts of a new file are written to space that became available when older files were deleted. Defrag can also try to put all of the small chunks of data making up files next to each other & in order. That helps speed things up, since the read heads on a conventional hard disk aren't jumping around quite so much. This operation can vary from one defrag app to another, or as with Smart Defrag Pro, you may get a choice of a faster defrag -- putting all the pieces of files next to one another is more work so it takes longer. When each file is stored that way, there are going to be some small gaps of free space that are too small to fit any of the available files -- some defrag tools can try to fill in every gap, leaving more files fragmented afterward. Smart Defrag Pro also gives you the option to just defrag individual files &/or folders.
Conventional hard disks work internally kind of like a record player, with round platters instead of a vinyl record, and with data stored in concentric rings, kind of like the grooves on that record. As with the record player, the disks [platters] rotate at a fixed rate, and the circumference of those rings increases as you move outwards from the center. This means that some data [files] can be read faster than others, depending on where they are physically located on the hard disk platter(s). While they use Windows' API, unlike Windows, 3rd party defrag apps like Smart Defrag Pro can try to move those files that matter most to the fastest part of the hard disk platter(s), which can speed up tasks [Windows, apps, games etc.] involving those files. There's no standard way of doing that however, so mileage can vary from one brand of defrag app to another.
With an SSD, data is written to physical storage locations based on whatever wear or load leveling formulas in the SSD's firmware -- since SSDs wear out, you want to spread that wear across all of the SSD's available storage, rather than say have a third or a half of the SSD wear out while the rest has never been used. [Note that it's recommended to only use about 1/2 of an SSD's available storage.] Running defrag on an SSD isn't *usually* needed, though the only harm it does is to contribute to wearing out that SSD. Win10 itself will defrag an SSD about once a month -- Microsoft engineers say it's necessary for Win10 to work as designed. [That came to light this year when there was a (just recently fixed) bug in Win10 2004/20H1 causing SSD defrag every time Win10 started (!).]
Apps like Smart Defrag Pro & Win10's Disk Optimize run TRIM on SSDs instead. TRIM is also run by the firmware in most SSDs, so even if you never run TRIM in Windows, it's still most likely getting done. When you delete a file in Windows, it's only removed from a sort of Table of Contents that lists where each chunk of data making up each file is physically stored -- that's why file recovery apps can work. It's no big deal with a conventional hard disk, since writing new data overwrites old, but with SSDs it's a two step... it's one step to delete the old data, and a 2nd step to write the new. TRIM preemptively deletes old data so writing new data only takes a single step.
[Note: Reading the online manual I read that the app monitors disk health, including temp. [I assume S.M.A.R.T. data], but did not see this in the app itself.]
Smart Defrag Pro also lets you monitor hard disk & SSD health. There's a small, free, portable app called Crystal Disk Info that you can use instead if you like. Hard disks and SSDs record some data in their firmware, though what's stored varies by make & model. These apps can read this stored & current S.M.A.R.T. data, which *sometimes* can warn you of impending trouble.
If/when you compare defrag apps/tools, the very basic parts aren't going to vary from one to the next -- they use Windows API to accomplish the same things, and the *exact* same task is going to take the same amount of time regardless which one you use. Smart Defrag Pro lets you do a sort of light defrag that takes less time, and most 3rd party defrag apps offer some sort of optimization, putting what *they consider* the most critical files on the fastest part of a conventional hard disk -- Win10 doesn't do either. Whether Smart Defrag Pro's optimization works better than something like Auslogics' is up to you. Some defrag apps can also run in the background, doing their thing when the system's idle. How much that matters depends on the amount of data you have stored on conventional drives, and the performance of those drives -- some drives are faster than others... nothing however is going to make defrag happen any faster than the speed of the drive will allow.