In theory it shouldn't, but we all know how theories go...
In theory, installing lots of different programs shouldn't destabilize the system, regardless of how they're installed.
Reality, on the other hand, says otherwise.
The real answer is, it depends more on the specific software you install then how you install it.
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Today's systems are incredibly complex. Installing lots of software can easily destabilize them. In addition, UNinstalling software can also contribute to instability or "software rot". Avoid experimenting with lots of software, try portable versions if available, and of course back up regularly. Within reason, install and evaluate what you need and use.
Software rot
What you're talking about has a name: "software rot."
The problem is that today's systems and software are incredibly complex. That means installing software -- even if it's just the first run of a portable application (the kind which requires no setup program) -- is also complex.
And subsequent updates and uninstalls add to the complexity.
As a result, it's easy for settings -- both the settings you see and the thousands of internal settings used only by the applications and Windows -- to get confused. Depending on the software you're running, that confusion can result in nothing at all, or it can cause the software, or even Windows, to misbehave.
Trials
The most common culprit is installing and uninstalling software you just want to try out.
It's important to evaluate software to see if meets your needs. To do so, you'll typically install it and run it. If you decide it's not what you need, uninstall.
If you do this often, it's a bigger cause of system destabilization (or "software rot") than simply installing and keeping the software you use regularly up to date.
The good news is, things have improved in recent years. I frequently install and uninstall software, and rarely suffer for it. Don't stop trying things out; your machine needs to meet your needs.
I have one recommendation, though.
Back up
Before you install something you're just trying out, back up your system completely. Ideally, you're already doing this by virtue of having a daily backup solution in place.
That way, if something does go wrong with the trial or its uninstall, or it happens to include PUPs, malware, or worse, you can quickly, easily revert to a state prior to whatever happened.
And besides, things can always go wrong completely unrelated to software installations, trials, or software rot. Backups protect you from it all.
Portable apps
I do want to share a thought about portable apps.
A portable app is an app that requires no setup or installation process. You simply copy it to your machine and start using it. To "uninstall" it, you delete the files or folders you copied.
In theory.
The problem is, portable apps often install things or set things up the first time you run them. In a sense, there's still a setup process; you just don't see it.
In general, portable apps are designed not to do much in the way of setup, but there are no guarantees. That's why I fall back to being more concerned about what software you're installing, not how much of it.
Unfortunately, it's nearly impossible to determine how an application will behave prior to installing it. But if your portable, no-install-needed app suddenly includes a link or instructions to uninstall, chances are it has done something in the way of installation.
My recommendation
Within reason, install and evaluate what you need and use. Use your computer the way you need to. Don't spend a lot of time worrying about software rot -- expend that energy on staying safe instead. That's probably a larger risk these days.
Just make sure to back up along the way. That'll protect you from much more than software rot.
Do this
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I’ve noticed the software rot problem to be significantly improved in Windows 7 (and possibly Vista) and beyond, than with previous versions of Windows. It seems to have a self cleaning oven. This may be anecdotal and not really the case. Does anybody else out there have similar experience?
22-Apr-2013
I have the same experience. Been using windows since 3.1
From vista onwards no significant problems ie instability like crashes and /or blue screens. Software related of course.
I seems that with every new version the quality and reliability increases. A bit like cars I guess. Must confess that I don’t fool around anymore with registry cleaners and the like . One of the things I learned from Leo’s articles!
Portablefreeware.com is a great site for ‘portable apps’ (god, I hate the word ‘apps’, it just sounds weird) and it’ll tell you if it writes to anywhere besides the application folder.
I like to use RegShot, which takes a snapshot of the registry and then compare it with another. I just like to know what’s going on with my computer.
I fully concur that Windows 7 reduces, if not eliminates, software rot. It is by far the most stable operating system I have ever used, and I go back a few years when I say that – all the way to 1965.
My Windows 7 has remained very stable ever since I stopped using so called registry cleaner programs. (At one time I had to reinstall Windows due to the mayhem caused by a registry cleaner!) I recommend you don’t use them and you will be a happy user it you don’t.
If you install a lot of programs under Windows 7, even if you deinstall them later, your windows\winsxs directory will grow uncontrollably. AFAIK there is no solution other than a clean reinstall (or restore of an early backup).
Regarding Leo’s suggestion to forget Apps, I would like to know if add-ons are the same as apps. I have three add-ons to my Firefox browser, and I feel they are a big help. I also have used a Kindle app via my Firefox, and this enables me to read Kindle books for free without even putting an actual Kindle program onto my computer desktop. Would these still be enough of a safety problem to get rid of them? I’ll do whatever you say, Leo.
I was wondering what exactly it is about the installing then removing of programs that causes the problems…and if you use a thorough uninstaller such as Revo, would that make any difference?
@Natalie
The Apps Leo is talking about are Portable Apps. He’s not saying anything against them. They are perfectly fine to use. What he’s saying is that it’s just as safe to use the installed version as the portable version of these programs. “Portable apps are great, but they don’t necessarily offer a significant increase in system stability by avoiding the setup process.” He’s simply saying that you can install the programs and be just as safe.
As for browser add-ons or extensions, a well-designed add-on is harmless but a poorly designed add-on can degrade the performance of your browser.
@Bonita
The problem is that many freeware and some shareware programs don’t necessarily uninstall completely. A well-designed program should uninstall with no harmful traces. A program like Revo Uninstaller can help but there’s no guarantee it will get everything.
I slightly disagree with Leo.
Installing software can sometimes also cause problems. Not rot, but it seems that so many programs these days like to put themselves into StartUp or the Run registry key so that they run when you boot up your computer.
They say they are doing you a favour by pre-loading some components of the software so that it runs faster when you go to use the software. But the reality is, sometimes you are just turning on your computer to check your email and don’t need five different programs to take the time to load up into memory or check for program updates (e.g. Flash) and slow down your computer.
I recently started from scratch on my Windows XP computer and I took the time to evaluate how I used that computer (I also have a laptop that I use regularly) and look at what software I was putting back on the machine. If another piece of software duplicated a task, I only installed one. I only use Excel on my laptop, so I didn’t bother to install Excel on the XP computer, for example.
What I ended up with was a cleaner machine that is quicker to boot up so I can do what I really turned the computer on for, not what some software vendor thinks I might want to do.
12-May-2013
Beginning with Windows 8 and newer, firing up the Task Manager, CTRL+SHIFT+ESC, and clicking on the Startup tab will show you the programs which start up with Windows. Right-clicking on a program and clicking Disable will prevent that program from starting up with Windows. It’s difficult if not impossible to locate all programs which start with Windows, but this will get most of them.
These articles give some ideas on how to determine which programs you can disable from starting up with Windows:
What Can I Disable in Task Manager’s Startup List?
What Windows Startup Programs Do I Need?
This process is relatively harmless. If you find you need that program to start with Windows, you can always go back and re-enable it but I recommend backing up just in case.
A suggestion.
I use Sandboxie to test programs before deciding to install them on Windows (and have since XP).
I have a full license for Sandboxie, but I believe it is now free for everyone.
Leo says “The problem is that today’s systems and software are incredibly complex”. Well, that’s not the reason why there is “software rot” on Windows computers. The reason is the Windows OS design and rules (or lack thereof) for software installed on Windows. The big elephant in the room is (drum roll) … The Windows Registry. This ill-conceived, poorly executed kluge of a “database” is the source most problems. The reason is that not too many software vendors know exactly what is in there or how it works, and yet they are free to muck with it as much as they want when installing or running software. The other part of the problem is the fact that originally Windows never prescribed hard rules for software being installed on its OS (like Apple). A software installer can write or change just about anything on the system, including overwriting system DLLs with different versions. Granted, in recent editions of Windows Miscrosoft has tightened the installation rules a bit, but too little and too late. So, when you install software, the setup program can install and change anything, anywhere. Most vendors deliberately spread out their tentacles far and wide to make sure that complete a uninstall is impossible (not a conspiracy, just a bad and undisciplined legacy design). The result is that when any one of the linkages between the many pieces of installed software is broken, the system starts misbehaving.
Briefly, let’s compare that with how software is (traditionally) installed on Linux systems: All the software for an application is placed in one folder. Some software may require additional links into other OS folders, but these extensions are few and completely modular so that they don’t change the OS pieces. Result is a more stable system.