With the advance of solid-state drives and the falling prices of conventional hard drives, adding extra storage isn't complicated. However, there are users who manage to consume every last byte. A classic maintenance question is how much space should remain free on a Windows PC. Unfortunately, it's not so easy to answer because software is a moving target, but that hasn't stopped us before...
I have no space, what do I do?
All computer users have lived that situation firsthand. Adding drives is a matter of finding the best price-to-performance ratio, but if the budget is too tight and you can't invest in a secondary drive, you can always do stricter management and analyze disk space with WizTree, which will identify the most problematic elements in seconds.
When space runs low, the system drive starts to store videos, games, music, and images, but that content competes with Windows itself, its massive updates, and every change Microsoft decides on a whim. So what's the limit? How much free space should remain for things to work reasonably?
How much space should you leave free on your PC?
Honestly, I don't think even Microsoft knows for sure. In Redmond they've only suggested minimum space parameters for certain tasks (like installations), but there's no greater precision. Perhaps their firmest data is when defragmenting. The official documentation (now available via Archive.org) indicates that the defragmenter needs 15% of free space for the complete process, otherwise it will do a partial defragmentation.
In the case of solid-state drives, this is irrelevant because they don't require classic defragmentation, and old guides point to 25% of free space, although in recent years SSDs have improved their speed and capacity, leaving behind the ghosts of degradation.
Hard drives still have plenty to offer
At the same time, we must emphasize that it's no longer worth talking in percentages, but in net space. After all, 15% of 3 TB is 450 gigabytes, and there's no sense in wasting them following an arbitrary rule of dubious origin, even if it's a slow drive.
What do I mean by 'slow'? One of the main suggestions to speed up a computer is to replace its system hard drive with an SSD. That change is especially useful in laptops, since most manufacturers use 5,400 RPM drives. Now, if that drive is in good condition, it definitely can take on another role.
Think of applications of high density and low access speed. Movies, series, and music. Putting an SSD on everything is very tempting, but it would be a big mistake to let a 1 TB drive sleep when we lack space. It just needs to be filled with the right information.
In summary
With a proper storage strategy, you'll discover that you'll never be forced to answer the original question... but if you really want my opinion, I'll only say "all you can afford, without exaggerating".
We all know that a hard drive works better when it's empty. Its speeds aren't constant, and if we add a partition full of data combined with the effects of fragmentation, its performance inevitably declines. But that loss is much more tolerable if we focus the drive's use on storing data that doesn't demand high burst levels, or very low access times.
That said, the drive with the operating system, the swap file, and the hibernation file needs to respond as fast as it can. This is where the hybrid SSD+HDD combination shines. A good solid state for Windows and games, accompanied by a hard drive in charge of handling the heaviest stuff on your system, will make a fabulous team.
