What is Unallocated Space?

When you're installing an operating system on a new harddisk, do you notice that the installer said that our disk status is Unallocated? Or when you want to divide a harddisk into two or more partition, after the split the newly created partition also in the "Unallocated" status. So what is this unallocated called thing?

Unallocated space, or in the other word "free space", is logical space on a hard drive that can be used by the system to put files on. Unallocated space is the opposite of "allocated" space, which means a place on the hard drive where there's already files written or stored in it. Unallocated space is different from Slack space. The difference, in the unallocated space the system can put files in it, where in the slack space the system can't put any files in it. Simple right?  :)

Here's an example. If we put a file into certain space on the hard drive, that part of the hard drive is now in allocated status because the file is using its space. When a space is in allocated status, no other files can be written to that space. If the file we stored is deleted then that space of the hard drive is now in the unallocated status. This means that we can put some files in it.

Generally, files can only be stored in the unallocated space. New storage device is have all its space unallocated virtually, why? because small portion of the space will be taken by the system files to do its work. Like when in windows there will always be a "recycler" hidden folder to store a data about deleted files, or in linux called ".Thrash". 

cmiiw

Example case. A newly formatted 100 GB flashdisk have 100% unallocated space (actually its 99.9% because of the filesystem). If a 1 GB file is stored on the disk then there will be 1%(1GB) allocated space and 99% unallocated space(99GB). If a 9 GB movies is stored to the disk, then there will be a total of 10%(10GB) of allocated space and 90%(90GB) of unallocated space. So, the movies will only be stored into the remaining unallocated space, not overwritting the previous one.

So, what will happen when a file is deleted from the hard drive? Using the above case, if the movies were deleted. There will now be 1% allocated space and 99% unallocated space again. However, the deleted file didn't just disappear, it just canges its status. The data of the movies is still exist in the unallocated space and will still be there until new files are written in the space. When there aren't any files overwritten the space then the movie file can be recovered with some tool.

And that is unallocated space..  :D

"the quieter you become, the more you are able to hear.."