Windows 10: Windows decided to compress some of my files on its own...?

Today I launched my PC and I noticed that some of files on the desktop have these two blue arrows pointing at each other located in the top-right corner of the icon. Based on my quick research in Google, I discovered that these mean compression. But... I haven't set them as compressed by myself. Why has Windows done it?

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:)

 

Some files listed in Windows Explorer are blue font

I seem to have run out of room on a Windows XP Pro system. I tried to defrag but don't have but 7% room available. I looked in Windows Explorer to try to find some huge files that might be corrupt and I see a few that are listed in blue. What does that mean? I have not compressed anything on purpose. Thanks

 

Compress files??

It all depends on the contents. Back in the early days of DVD games, they had plenty of space compared to CD's. So they left stuff uncompressed on the DVD itself. Compressing such ISO image would result in very high compression ratio. But these days, even DVD discs are becoming small and game companies are already using data compression to fit more data on the same DVD. And since you cannot compress already compressed data, you're seeing more and more of the 99% compresion ratio moments.

Good examples of such scenarios is when you want to compres uncompressed WAV file and a MP3 file. WAV is not compressed and you can decrease its size significantly. You might gain few kilobytes when trying to compress already compressed MP3. The same is with images. You can compress BMP images rather well but when compressing JPG images, you won't really gain anything as its already compressed.

There are few very specialized algorithms that may gain some more compression out of already compressed data, but the gains are usually very small and usually not worth the extra compression time needed to perform the compression itself. Plus you can only use them to compress very specific data files.

 

So I used KGB Archiver to compress a 10gb file into a 40mb file...

Exactly. Most compression programs change a series of 1s and/or 0s to a couple of digits, and stores the total file in a table of contents/index. If you've got a file with TONS of repeating digits, sure, but pictures? No way to get that kind of compression in the real world.


from an article on "How To Geek"

First, we installed Bastion and compressed its folder — about 863 MB in size of music, graphics, executable files, and various different types of documents:

• Zip (Windows 8.1): 746 MB (86.4% of the original size)
• Zip (WinZip): 745 MB (86.3% of the original size)
• RAR (WinRAR): 746 MB (86.4% of the original size)
• 7z (7-Zip): 734 MB (85% of the original size)

Next, we compressed Hotline Miami, which is 654 MB of data:

• Zip (Windows 8.1): 316 MB (48.3% of the original size)
• Zip (WinZip): 314 MB (48% of the original size)
• RAR (WinRAR): 307 MB (46.9% of the original size)
• 7z (7-Zip): 301 MB (46% of the original size)

I would not expect a great deal of change from those numbers in November of 2014 to now, nor would I expect any real-world files to come any where NEAR the compression rate of .4%.