You're probably thinking: Wait, what's the difference between RAM and hard drive space?
RAM is used as temporary storage ("memory") by your computer, which determines the amount of applications and services the computer can have opened and running. The higher your RAM, the more memory capacity your computer has and the more efficiently it operates.
Hard drive space, on the other hand, is physical storage space, which determines how many files you can permanently store on your drive.
So what happens when your computer runs out of RAM?
The easy answer to that question: Your computer will start to work less efficiently. That's because when your computer runs out of memory it will start to use the hard drive space for "virtual memory" to compensate. While in theory this sounds fine, in reality your hard drive read/write speeds are much slower than the RAM read/write speeds. Slower speeds mean exactly what you'd think: you hard drive activity LED will flash continuously and your computer will slow down - and the more virtual memory your hard drive needs to use, the slower your computer will get.
This lower operating efficiency doesn't just mean slower performance. It can also lead to, among other things, an inability to burn CDs or DVDs, install software (either via Software Update or using third-party installers), and to enable or disable FileVault®.
These problems are even more likely to occur when your startup disk is also nearly full and any free disk space is taken up by swap files.
So what can you do to fix the problem?
There are only a few permanent solutions out there. Most obviously, you'll have to add additional physical RAM into your computer - ideally up to the maximum limit your Mac will accept. You can also purchase a larger hard drive for the Mac OS X startup disk or an additional internal hard drive for data files. But in the meantime, try running as few applications as possible until you can implement a permanent solution.
Compared with running out of RAM, running out of space on your hard drive is not a big deal. For starters, you can clean up your current storage, including doing the following:
- Remove photos or save them to the cloud
- Delete files from your "Downloads" folder
- Erase attachments from Mail
- Quit applications that are needlessly running in the background
- Remove additional languages you don’t need
- Tidy up cache files
- Erase old iTunes Library backups
- Disable "Diction"
- Empty out the "Trash"
But the most efficient way to clear up space on your hard drive is not to do it at all - get a TarDisk! That way you don't have to ever worry about running out of hard drive space. As an added bonus, your computer will also run faster when using a TarDisk because the hard drive will no longer be using any virtual memory.