Helping people with computers... one answer at a time.
After updating IE7 to IE8 some folders and setting may be left that make it appear that IE7 has not been completely uninstalled. We'll speculate why.
I recently reformatted my HD and reinstalled Windows XP Pro. My install disk included SP2 so after the XP install completed I installed SP3 and then IE7 in that order. Then I installed all necessary updates, patches, etc. I later decided to install IE8 and I've kept that updated as well.
Today I needed some system info so I ran a free utility called System Information for Windows. According to the printout, my machine has IE7 and IE8 installed. This surprised me because only IE8 is listed in the control panel add/remove applet.
I opened my C:\Windows folder and sure enough, it shows that I have a folder for IE7, IE8, and update folders for both.
Question 1: Does each new IE build upon previous versions during installation? I thought each IE is a stand alone product.
Question 2: Since IE8 is a Windows "product" I'm guessing it used the Microsoft Windows Installer to.... well.... install it. Shouldn't the installer have uninstalled IE7 as part if the installation process? Does the fact that it didn't mean the IE7 files have to remain?
Question 3: If I had installed IE8 over IE6 and bypassed IE7 entirely, would the IE6 files have remained instead?
Question 4: If IE8 is a separate installation and not dependent on previous versions to run properly, would it be safe to remove all IE7 folders just to add some more free space on my HD?
An interesting scenario that had me firing up my Windows XP / IE8 testbed to see what had happened there. I'd actually gone through the XP "original", SP2, SP3 path ... and ended up with the same results.
I'll answer those questions, and speculate a little on the how and why of the situation.
First, let's simply acknowledge up front that software installation, update and removal is a messy task. There are many assumptions and decisions to be made, not all of which are clear, but ultimately have some kind of rationale.
That being said, let's start with the four questions you asked:
"Does each new IE build upon previous versions during installation?" Yes and no. No, in the sense that the software is stand-alone. The components that make up IE8 may replace the prior components in IE7 as needed, or may replace all components regardless of what was there before, but conceptually it doesn't "build on" what was installed before; it's a separate stand-alone installation. Yes, in that things like your user settings, configuration changes and options are for the most part preserved.
"Shouldn't the installer have uninstalled IE7 as part if the installation process? Does the fact that it didn't mean the IE7 files have to remain?" Yes and no. Uninstall followed by install is only one approach to updating software. It's quite possible that instead the installer simply updated in place - meaning that without uninstalling anything it simply replaced those components that had changed from IE7 to IE8. Even so, I wouldn't take any of what we're seeing here to claim that it did uninstall IE7 or that it did not. What you're seeing could be the result of either approach.
"If I had installed IE8 over IE6 and bypassed IE7 entirely, would the IE6 files have remained instead?" It's unclear, but I'm thinking not. I say that because my test system started with the original pre-SPanything Windows XP which came with IE6. I updated to IE7 and then IE8. On that system I find only ie7 and ie8 and ie7update and ie8update folders, as you did. I'm speculating that the installation and update process changed somewhere between IE6 and IE7 to account for the difference.
"If IE8 is a separate installation and not dependent on previous versions to run properly, would it be safe to remove all IE7 folders just to add some more free space on my HD?" Maybe. Maybe not. I'm guessing, again, that it is safe to do so based on my own little experiment: I renamed the two folders, and nothing broke. I moved the two folders out from the C:\Windows folder and rebooted, and nothing broke that I could tell. As with all "is it safe to delete this" questions I recommend that you backup a copy before deleting it from your hard disk just in case you find later you really wish you hadn't.
Now, for some more rampant speculation.
Just what are these folders?
My guess is that they are folders of information used should you ever uninstall IE8, IE7 or one or more of some of the patches that have been applied to them. In other words, they're probably simply folders that contain data that you don't need every day to run the product, but that you might need some day if you ever need to back out of an update.
Hence the advice to back them up to some kind of offline storage to free up space might make the most sense. (Though to be fair, these folders take up less than 100 megabytes on my machine, so it's hardly worth the effort given most large hard disks these days.)
But as you can see, I started this article with the thought that install, update and uninstall can get messy. When an update or uninstall program is made, it has to include some decisions about whether or not to support things like preserving your settings, migrating your settings, allowing you to roll back to prior versions, and just how seamless that should all be. It's that "preserving your settings" decision that, in some cases, confuses software inventory programs into believing something's installed when it's not. The tool finds your old settings preserved in the registry under the old version for potential roll-back and takes that to mean that the software is still around.
Bottom line: I'd leave the folders alone, but if you're really itching to delete them just back them up somewhere first.