Under disk cleanup there is an option to compress old files

Hi Carsonian,

Unlike the other categories under Disk Clean Up, 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.

When we set to compress old files automatically by windows disk cleanup, it might compress some system files which are not accessed for certain period of time and deleting that might cause issues if not immediately.

Note that when Compress Old Files is highlighted an Options button appears.Clicking options will allow you to set the number of days to wait before an old file is compressed.

This feature was there in Windows XP, the newer version of Windows like Windows Vista or Windows 7 does not have this option under Disk Clean Up.

Hope this information is helpful.

Amrita M

Microsoft Answers Support Engineer
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I personally do not compress files and probably never will - if necessary, I'll just get a larger hard drive (or another hard drive or an external hard drive).  As long as you compress only the correct files (not your boot files or anything like that), I suppose it's safe enough - but they take longer to open - not a lot but some and it depends on the size (they need to decompress) andthere's always a risk when doing something like that that some form of corruption will occur (which gets us back to the old mythology but the risk is generally considered minimal and I don't mean to overstate it - but it does exist).

Opinions vary between the experts and you'll get them from either end of the spectrum.  Some will tell you it is perfectly safe and a good way to save space on your hard drive.  Others will take a middle road and say they aren't positive but think it is safe but recognize that there are exceptions.  You may see some responses like that posted here.  As I said, I personally willnever do it (except for certain files which I may compress for e-mailing or because it's large and I never expect to need it again or for other reasons - but they would be individually selected and done for a purpose {and using a different program]).  I mean I would never use the generic disk cleanup compress old files option to do it on a somewhat global basis with no individual selection (and when I do do it with an individual file, it is quite rare - I probably haven't done so in over a month - and to be perfectly honest, when I do compress a file for e-mailing, I first make a copy and compress the copy and retain the original uncompressed).  I've also seen situations here where people have compressed their boot files along with pretty much everything else and this has caused them a lot of grief - it's not an easy process to repair and the system won't boot with those files compressed (I'm not sure how they did it - I just saw the posts but didn't read the threads - but if there's any chance that the Disk Cleanup compression was involved (and I don't think so but I didn't read how it happened and so I suppose it is possible), then that's just another reason for me to stay away).  As you can probably tell by now, I don't really trust the process (perhaps I still have some of that old office folklore in me as I was around when it first came out and had all those problems) and would rather spend money on a bigger or second hard drive than to compress my old files.  I'd rather take no chances I don't have to concerning my data which is precious to me.

The process is availalble and is generally considered reasonably safe when used correctly - but not a lot of the experts I know do so.  It's MUCH safer than when it was first released.  When we suggest ways to save space on hard drives for people who are short on space and don't want to upgrade or get another one, it is rare to see anyone suggest compression as one of the options (I never do).  We suggest many other alternatives, but I never see this option emphasized or specifically suggested (though it may be included as an option in processes we do suggest like Disk Cleanup - and I don't specifically discourage its use either though you've heard what I'd say if specifically asked).

Ultimately, the decision is yours.

I hope this helps.

Good luck!