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Should I check "compress old files" option while performing disk cleanup on Windows XP? What are the pros and cons?

Likewise, there is another option in Local Disk Properties window: "Compress drive to save disk space". Is it also reasonable to check it?

Options for Disk Cleanup

Starting Disk Cleanup from a drive's context menu/Properties

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up vote 11 down vote accepted

Selecting this option basically compresses all old DLL and SYS files in the Windows folder that hasn't been accessed recently or ever. It uses the normal built in NTFS compression, and to be very honest on today's hard-drives has little or no impact on the folder sizes. These files already take up minimal space.

The How-To Geek has an article here describing how to tweak it. The more precise description from the The Elder Geek here is:

Unlike the other categories, Compress Old Files doesn't delete any files from the drive. It compresses files that Windows hasn't accessed for a specified period of time. The files are still available, but there will be a slight increase in access times because the files will be decompressed the next time they are accessed. Note that when Compress Old Files is highlighted an Options button appears. Clicking it will allow you to set the number of days to wait before an unaccessed file is compressed.

To answer the second part of your question, NTFS compression is reasonable if your storing a lot of data like Music, Documents and Videos and should NOT be enable on your OS drive. If you have a second drive just for storage it can be enabled, however the compression ratios are extremely small. You will not see 100GB's of space saved using this feature, and it is not as compact as zipping the files for example.

Among others, SQL Server does not allow it's database to be stored on NTFS compressed volumes as the performance on decompression is extremely expensive.

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It may have little impact on free space, but in this day and age the disparity between processor speed and disk speed is so great that turning compression on is a no-brainer. The access will in most cases be faster than access to files with no compression. The only exception is very small files and files that are compressed anyway, such as ZIP or MP3.

You will probably not notice any speedup, though, because the option in question concerns only DLLs and system files that have not been accessed recently (so it's a good bet you won't need them in the future either). You have a better chance of actually having a faster computer by compressing everything.

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Pro - you save space.

Con - when you access those files they need to be decompressed, so access is slower.

Should you? As always, it depends. You need to consider how often you access "old" files and whether (slightly - it depends on your machine) a slow down in the access of these files matters to you, but the most important factor is probably how great your need of the spare disk space is.

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They need to be decompressed, but with the difference in speed between CPU and disk being ever greater, the time to read additional blocks of the file from disk will be in most cases (except very small files) actually greater than the time to decompress the file. Especially so if the disk is fragmented, and it needs several seeks to read the file. So I don't really see any cons to turning off the compression. Except, if you want to fine-tune it, very small files and files that are compressed anyway, such as ZIP, MP3 etc. – ttarchala Oct 28 '09 at 11:38

For what it's worth, I run Windows on a virtual machine with an allocated minimal amount of space for "C:" (20 GB). I just turned on the option "compress old files" for disk cleanup, and went from 1.4 GB available space, to 4.22 GB which was good enough for my purposes :)

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Same for me as well. We run the command quite often here on our server systems (and my team has a lot of them). We often saw that a server running since 2-3 years get arround 20 GB free space (from a 50 GB disk) when the comand is run. Sure it might take CPU to de-compress the file, but if it keeps us from enlarging the diskspace in the next 2-3 years who care about that less CPU. The system already decided that the files aren´t really used... – BastianW May 8 '14 at 11:55

This is a old tech option that does very little in today's computers.

If you need more hard drive space, it's likely due to the fact you have a bunch of MP3 files or movies saved. Compressing the drive will not change that. DivX movies, MP3s, etc. are already compressed. All this will do is slow down your PC.

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