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I have a laptop running Windows XP (SP2) with 2GB RAM and a further 2GB page file. It's a company machine, so I have to work with what I'm given and can't add any more storage or memory.

What's the smallest amount of free space that I should have on the Windows C:\ partition before the system is perceiveably negatively affected?

In addition, what are the negative effects of low space - slow file manipulation? Slow startup? Crashes?

I know there are published 'minimum specs', but I'm more interested in the smallest amount of free space that actually makes a difference - i.e. having any more wouldn't be a benefit.

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You need enough free space for temporary files created by the OS. If you don't have enough space for that then the processes will fail, but in general it should not cause crashes.

Slowness yes before it is likely that your filesystem is more fragmented and new files created are scattered to fit into whatever blocks you still have left. There is no hard numbers, but you will likely see some problems when the free space is below 5-10% in my experience, but it really depends on your usage pattern. For instance, if all you do is browsing the web, then as long as brower cache is sufficient you are fine.

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temporary files might also include decompressed installation files: some (most?) installers need to decompress large amounts of data before copying or moving them to a final destination. In some cases this might be something approaching the install footprint of the application (if that app says x GB required, then you might need 1.5x-2x free disk space to install it) – horatio May 11 '12 at 16:33
Surely the amount of free space needed is an absolute rather than relative figure? If my HDD was 10GB in total, your 5-10% suggestion means I'd need 1 free GB - fair enough. But would I really need 1TB free if I had a 10TB drive?! – Widor May 11 '12 at 16:35
well, the assumption is the larger the disk, the more use you have and the more overhead you need. for instance, you would be downloading 1000GB files instead of 100GB ones in 10TB drives. In monitoring we always use the percentage for this reason. The system reservation is also in percentages. However using absolute free space is also fine, but my point is there is no hard and fast rules and all depends on how the system is used. – johnshen64 May 11 '12 at 16:59

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