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Automatically compressed files may or may not slow down a computer. It depends on the speed of the disk and processor.

This is a strange one. I've been told that my PC is automatically compressing every file and program, which means that it has to take the time to uncompressed files whenever I try and open them. I don't think I have consciously done anything to make this happen. Any ideas?

In this excerpt from Answercast #80, I look at a case where automatic file compression is causing some worry. There are ways to turn it off.

Automatically compressed files

Absolutely! If you take a look at an article I wrote some time ago called "Should I use Windows file compression?", you'll find the settings there that will control whether or not Windows will automatically compress all of the files, or a subset of the files, on your machine for you.

There's actually a setting in Windows Explorer that will display those files in blue, when they are listed, so that you can determine which files should be compressed and which files should not.

Compressing files

Should you do it?

In general, it's usually not that much of a performance hit. In your particular case, if you've got things turned on and the computer is working acceptably otherwise, I'd actually be tempted to leave it alone.

Now, it depends on the age of your computer. If your computer is say, I don't know, eight or ten years old, then you may want to consider turning it off - and that article will show you how. The issue is that, on an older computer, the processor is getting to the point where it's really doing more work (than you want) to decompress and compress those files when you write to them.

Compression may be faster

On newer computers, in reality, the processors are fast enough these days that in some ways, it's a wash. Depending on the speed of your disk, it can actually be slightly faster to have the files compressed.

The reason that "may be" is because: if the file is compressed, it's taking up less disk space. That means that to read a file, there's actually less disk that needs to be accessed. And disks are one of the slower portions of a computer overall.

So you're spending less time reading - a little bit more time decompressing. If the processor is fast enough, that turns out to be faster than on an uncompressed file.

On the other hand, sometimes it's the other way around. Right? Sometimes the processor takes more time. The disk is really fast and you're better off having the file be uncompressed.

Like I said, in general, unless you're experiencing a problem, my tendency is to say, "Leave well enough alone." But if you want to go poking around to see if this is exactly what you're experiencing and see what it might take to undo it... the article's called, "Should I use Windows file compression" and it should have the steps you need to take.

(Transcript lightly edited for readability.)

Article C6152 - December 19, 2012 « »

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Leo Leo A. Notenboom has been playing with computers since he was required to take a programming class in 1976. An 18 year career as a programmer at Microsoft soon followed. After "retiring" in 2001, Leo started Ask Leo! in 2003 as a place for answers to common computer and technical questions. More about Leo.

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