From Schaum's Os (6)

[naveednaseer]

Can anyone tell why it I sstated nine bits in question's 6.23 answer instead of 6 ( I guess so) because 3 bits for the owner,other group members and for everyone else and three bits for read, write, execute access thats make 3+3=6 why its 3*3=9. I am not getting it what to make of 9 bits.

[wood]

Naveednaseer,

For each type of permission (read, write, execute), you need three bits to indicate if the permission is granted to owner, group, and everyone. Take this example:

Read - 000 - not granted to anyone
Read - 100 - granted to owner
Read - 010 - granted to group
Read - 001 - granted to everyone
Read - 110 - granted to owner and group
Read - 101 - granted to owner and everyone
Read - 011 - granted to group and everyone
Read - 111 - granted to all

So for these 8 combinations, you need 3 bits. The same thing applies to Write and Execute and thus 3+3+3 = 9

Wood