I have a question about the use of du. I understand that du reports the number of 512-byte blocks of disk usage used in the directory and below.

However, with only 3 small files (file a is 64 bytes; b is 68 bytes; c is 6 bytes), du seems to tell me that the OS is using 8 blocks x 512-byte to store them. Is there anything wrong with my calculations or I misunderstand anything?

When I do a 'du' with no option, it gives me:
8 .
When I do a 'du -k', it gives me:
4 .
When I do a 'du -a' , it gives me:
2 ./a
2 ./b
2 ./c
8 .