Too much testing = too late a post in the comments, so in case it helps
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Registry Defragmentation does just that -- according to the web site it deletes empty spaces between stored data, much like the utility that comes with ERUNT [NTREGOPT.EXE], & it defrags the actual files. While it does do the 1st, rewriting registry data like NTREGOPT, I don't know if it relies on the newly written files to be unfragmented because they're freshly written, or if it actually defrags the new files in a 2nd step during the Windows re-start. In tests the re-written registry files are stored in Windows Temp folder, in my tests using [SysInternals] Contig.exe these fresh copies were unfragmented, a registry entry to run RegDefrag.exe is added to a RunOnce key with the Clear CLI switch, but deleting "Clear" those temp files were still deleted, & the registry's written to during Windows start, so I don't know how you'd find out if there was an actual defrag step or not. Running NTREGOPT after a defrag with today's GOTD, Before & After ERUNT backup folders were the same size in bytes, so apparently there was nothing additional for NTREGOPT to do -- Registry Defragmentation did its job well. Registry Defragmentation does have a couple of other features, but other than convenience I'm not sure if or why you'd want to use them... One does a backup using System Restore, the other provides a registry backup similar to ERUNT, but as far as I can tell without ERUNT's ability to restore a backup after booting to a command prompt &/or another OS. Testing in win7 64 I was also bothered by the fact that registry backups never seemed to be the same size, even running one after another, & they were always smaller comparing file to file with ERUNT backups, though in tests restoring these backups worked. Maybe certain keys like MRUCache are filtered out?
Registry Defragmentation itself is small, with 37 files, 1 folder, ~4 MB in the "Registry Defragmentation" program folder. New registry entries = 1 for uninstall, + 2 program keys under HKCU, & 1 key under HKLM. The md5 for RegistryDefragmentation.zip = 8e35908589ed3f09bb8cf0fb864281f2 . In terms of practicality, I'm not sure why most people won't continue using ERUNT & NTREGOPT, but Registry Defragmentation does let you select just what portions of the registry you want to work with, & that may be a benefit to some.
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#16: "For those who say defragmenting isn’t necessary. You are half correct. It really depends on how new or how old your hard drive is. While defragmenting an older hard drive will provide significant increase in performance, defragmenting a newer hard drive will not. Why? Because newer hard drives operate at 7200 to 10,000 rpms’."
FWIW, the drives I see on sale that are most popular are very often 5400 rpm, keeping cost down & capacity up -- After all, RAM's fairly cheap & SSDs take the place of small, 10k rpm drives. As far as when to defrag, it's kinda like when do you vacuum or wash your car? Some keep it spotless, others wait until it's dirty. :-) Some people like to keep a defrag app running in the background, or as a screensaver etc. -- they don't *Need* to, but they like it that way. Other folks wait till stuff starts slowing down, sort of the equivalent of someone writing Wash Me in the dirt on your back window. If you don't want to wait that long, Windows &/or most defrag apps will tell you how bad things are before they do anything, so you be the judge.
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#23: "You can not compact the registry while windows is running, period. All compaction must be done before windows loads. This software is not proper for compacting the windows registry."
The idea's rather simple, as explained with ERUNT -- you read all the data in the registry, which means skipping any/all spaces, & rewrite it to new files. During a re-start the new files are swapped for old. In fact you do the same thing restoring an ERUNT backup, as it's written the same way, without blank data. Maybe another way to think of or demonstrate the idea is create a new text file, open it in Notepad, & press the Enter key a hundred times before you type "Test". Save it & open another new text file and type test on the 1st line & save. Now compare file sizes in Properties. Reserving a space for data, whether you enter any actual data or not, takes up room.
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#25: "... how much space is actually saved by using this program. With the sizes (and speeds) of today’s hard drives how much difference does it really make. I can see using it as a possible fix to try if a computer is REALLY slow and hanging up but as a weekly preventive maintenance program I wonder…"
The idea very basically is this: open both an empty .TXT file & one with 20 MB worth of content in Notepad -- which opens faster? If the registry is smaller, that's better. Will it make a huge difference? Probably not -- best to think of it like eating a healthier diet... cut the calories just a bit in one meal, you'll never notice, but cut the calories a little bit in every meal, every day, & you'll probably not gain as much weight longer term.
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#26: "... It would appear that Elcor is locking up these structures while manipulating them... Nothing beats SysInternal’s PageDefrag... PageDefrag only fully supports up to XP..."
I believe that Registry Defragmentation simply writes copies of the registry file, then swaps them out on re-start, same as the ERUNT apps -- I don't know how you would confirm whether it did a separate defrag or not, whether during the writing process or before swapping etc.
PageDefrag OTOH is a bit old, having not been re-written or re-visited in years, despite other SysInternals utilities sometimes being updated a few times a year... Could that be an indication it's not really that useful? As Microsoft details here, it's not a big deal to have Windows delete the paging file on exit -- wouldn't a freshly written file tend to be unfragmented from the start, plus you've got the security benefits -- export the registry key the KB talks about set both on/off & you could delete the page file once a week or once a month if you'd rather.
http://support.microsoft.com/kb/314834#appliesto
