Observed space abnormality while mounting disks

Hi Team,

I found some space abnormaility while mounting disks.

I will try to explain my query with an example.

Initially I created one disk as follows

Command (m for help): n
First cylinder (4171-4865, default 4171):
Using default value 4171
Last cylinder or +size or +sizeM or +sizeK (4171-4865, default 4865): +820M

/dev/sda11 4171 4271 811251 83 Linux

I formatted the disk:

mkfs.ext3 /dev/sda11

In parted -l it is showing as:
Number Start End Size Type File system Flags
11 34.3GB 35.1GB 831MB logical ext3

Now I Mounted that disk:

mount /dev/sda11 /test1

df -h output:

/dev/sda11 780M 17M 724M 3% /test1

Please find my query as below:

Allocated disk: 820M
showing 831MB in parted -L output (First abnormality)

after formatting disk, I know 5% will be reserved for super user i.e 41MB

820-41=779 is allocated in /dev/sda11, showing used is 17M(say it nondataoverhead),
Upto here everything is fine.

Now
780MB-17MB=763MB(it must show this much free space),
But it is showing 724MB =>Means 39MB losing here, without any reason.

For 1GB disk we are losing 45MB

Then coming to 1 TB disk-->4510010=45000MB=43.94GB
10TB disk -->430GB(almost 0.5TB)
where this space is going on, what is the purpose of this disappeared space??

(I didn't find this much utilization is AIX, it is allocating 99.99% space while mounting)

Hope I am clear, Waiting for your valuable suggestions.

Regards
Satish