3Gb of disk space lost! Disk space problem or mother board conflicts with HDD

I've got Seagate hard drive (80Gb) and motherboard Chaintech 7VJL5 (VIA KT400A+VT8235).

Here is my drive partitions:
Disk /dev/hda: 80.0 GB, 80026361856 bytes
255 heads, 63 sectors/track, 9729 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot Start End Blocks Id System
/dev/hda1 * 1 2433 19543041 83 Linux
/dev/hda2 2434 2556 987997+ 82 Linux swap
/dev/hda3 2557 9729 57617122+ 83 Linux

And here is my disk space usage:
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/hda1 19236308 2606036 15653120 15% /
/dev/hda3 56712220 23488628 30342736 44% /home
none 257288 0 257288 0% /dev/shm

As you can see the size of my /dev/hda3 partition is 54.08 Gigabytes, but the sum of used space and free space is 51.34 Gigabytes! Can anyone tell me please where are the lost 3Gb of disk space from /dev/hda3?

I assume your partitions are formatted as ext3. By default when an ext3 filesystem is formated 5% is reserved for root. This is done to keep fragmentation low as well as allow root to perform file maintenance stuff. You can change the amount of reserved space by using the tune2fs command. I do recommend you keep some reserved space.

Thank You michaelk!
You're right /dev/hda3 is formated as ext3. But why it's not good to have a reserved space? If i decrease the amount of reserved space to minimum, how can i then avoid fragmentation? Is there any disk defragment tools?
Thanks again!

It is good to have reserved space.

It really isn't required to defragment a linux filesystem. I've never found any documentation that explains size of reserved space vs fragementation, so I really do not have any suggestions on min size.

Thanks! You helped me a lot!