What are compressed files and how can I get rid of them?

Running XP Home Edition.
I chose a system tool called CleanUp.
It has a checklist of lots of types of files to delete: Recycle Bin, Temporary Internet Files, WebClient/Publisher Temporary Files . . .
I just assumed they were all similar categories and checked them all for deletion.
But one category is “Compress old files”
This seems to be an entirely different animal.
The CleanUp was running for an hour and I realized it was going nuts, not just removing files but compressing them.

I don’t want any files compressed. I have no disk shortage. I have a huge disk. I have only 8% of my disk in use.
Any compression can only mean one thing - lost time decompressing later.

Are my files ruined forever? Will they always be slowloading from now on?
Is there any way to undo the compression?

Select the file or folder. Right click. Select Properties on the dropdown menu. Click on the Advanced button. There’s a checkbox “compress contents to save disk space.” Uncheck that box by clicking on it. Click on the OK button. Voila!

This is not necessarily true. It depends on the relationship between your CPU speed and your disk interface speed, what your computer is also doing at the time, and how well the file compresses. The time spent decompressing the files may actually be less than the saving in time from getting a smaller file through the disk interface.

While we are on the subject of compressing files, how do I make XP stop offering to compress the messages in Outlook Express?

Thanks, and sorry for the hijack, but it didn’t seem new thread worthy

I’m not sure about that working, but you did solve my problem anyway.
I doubt unchecking the box would uncompress files that were already compressed, since it seems to be a flag rather than a command. It would only apply to new saves.
But it did give me a way to check my directories. None of them seem to have the box checked.
So I suppose I killed the compression program in time, while it was still deciding all the things it was going to do?
Or maybe it wasn’t running for an hour but in an error loop and idling.

It worked on my machine. I compressed & uncompressed a file doing exactly nothing more than check & uncheck the box. The names of the compressed files show up in a different color, blue in my case.

But note that this cleanup task applies to old files – ones that you haven’t used for quite a while. If you’re like most people, many (most?) of those files will never be opened again. So the time spent de-compressing the few that you ever open again (and de-compression can be very fast nowdays) is balanced against the space saved by having all of them compressed, and the time saved when doing weekly backups, etc.

It’s a flag, but it will be applied to existing files and subfolders - at least it can be. However, it seems that you can’t clear compression over a folder that’s already uncompressed, and the compressed files might be well down inside your directory structure. When I compressed a test subfolder, telling it ‘apply this to all subfiles’, and then compressed the parent folder, saying ‘just compress the folder listing itself’, then I could uncompress the entire parent folder including all subfiles and subfolders (including my test subfolder) but it had to go over all files descended from the parent folder at the same time, which took a little while.