Disk space issue?

I have a 40gig hard drive, when I go into the Properties, I see
Used space 31.6 GB
Free space 2.11 GB

1] Where's the the missing 5-6 GB's?

2] What can I do to retrieve the missing space or what can I do to gain more space on this drive? Thanks.

 

The missing space is holding the ntfs or fat32 partition table and cluster information. You'll never be able to access the full size of a disk. The OS has to reserve space for this information.
The bigger the disk the more space the OS uses to store this data.

 

What's the "least" amount of space required to run a pc efficiently? Meaning, when a HD is nearing it's capacity, there has to be a point at which things will not run 100%, anyone know how much free space is required for this not to happen? 2 gig, 1 gig, 500MB E.T.C?

 

Before an upgrade one of my servers boot drive was 18 gigs. It was at capacity which was 16.2Gigs and ran fine like that for 2 years until I took the server offline. Of course nothing was being written to the drive during the whole time. I had to move the logs to another drive since they grow.
Once you hit capacity you'll know because you'll get no space left on device errors if you try to write to it. As far as running at 100% the drive will run at 100% if it is at capacity. You just can't write to it.

 

I usually feel some pain when the system drive drops under 500MB. Because its such a pain to clean up a sluggish system, I usually start to watch out and delete/move stuff when I hit around 1GB of free space. Its a testament to the fast growing size of drives; I remember when having 1GB of disk in the whole system was a big deal (big pimpin' 200MB system/400MB data!)