I ask this because many years ago I heard such a thing. I have a 900GB hard drive and I am lingering around 40GB free space. Is this bad, will it harm the drive's health, or will it hurt my system's performance at all?
Will not having more than 10% disk space available on my hard drive affect performance? [duplicate]
Things that you might be concerned with would be if there's enough space for the swap file, hibernation (if you're going into low/no power states), and fragmentation.– ernieJul 30, 2014 at 21:43
Inside of any (non-SSD) hard drive are several disks spinning on the same shaft and a set of arms that fit between the disks. At the tip of each arm is a head, which reads the data off of the disk. The arms swing back and forth in such a way that the heads can reach every point on the disks.
When your disk is not very full, the arms only have to move across a small portion of the disk radius. On average, reads will happen faster than if they have to move across the entire disk, which occurs when the disk is nearly at capacity.
Filling your hard drive shouldn't harm it in any way, but, as stated above, it will tend to make it slower.
If speed is a concern, you could also consider defragmenting your drive (this page has instructions for Windows). Defragmentation moves items on your disk in a way that improves performance, without losing any data.
For Win7 at least (don't known about 8-s), defragment repeatedly until there is practically no change done - the repeats will be quicker per repeat.– HannuJul 30, 2014 at 18:02
I use a 256 GB SSD (although I assume you are using a mechanical hard drive since it is 900GB, which might work a bit differently), and I can attest that whenever I got low on space (generally below 20GB or so) my computer slowed down very noticeably. When I recently moved some files (~40GB worth) onto an external hard drive, the performance was back to normal. (I did not uninstall any programs, or do anything else that might have given me the performance boost. So it was just freeing up hard drive space.) So this effect is even true for SSDs.
It will not hurt your drive but it will cause a slowdown and other wear as it has so much to do. As mentioned in other answer, the head will have to seek more and more as files are not stored contiguously.
It won't directly hurt performance. But if your drive is almost full, it will split files in more fragments and therefore disk performance suffers. You can work around that by defragmenting more often. But that is a very intense process for the disk; if it's an old one, the possibility of failing is much higher (according to a Google study).
FWIW: If this a 'Win' machine's system disk, it is likely to crawl at least in some situations - or even barf out depending on which W it is.– HannuJul 30, 2014 at 17:58