The 4th bit should be on most Linux and Unix OS's. Usually 777 is really 0777.
Like mentioned aboved the "implied zero" can be set for elevated privileges - 4 = setuid, 2 = setgid and 1 = sticky. They behave differently on files and folders. Probably the only thing that isn't even remotely useful any more is setting the sticky bit (1) on a file. They used to that back in the day to load the program's libraries into resident memory so they would come up quicker the next time they were invoked. Not necessary any more, since having tons of memory, paging, swapping advances, etc have made this pretty much obsolete