Private-key encryption uses a secret key to encrypt and decrypt information. By assigning keys to services, it becomes possible to authorize an agent's access to a service by giving the service's key to the agent. The agent can then present the key to the service as proof that it is allowed to access the service.
Most answers agreed that encryption could be used to implement authentication, but explanations of how it can be done were less common.
The FAT can be optimized by essentially changing the data structure. Under non-contiguous disk-block allocation, the FAT is a cross between a bit map, keeping track of the free list, and a linked list keeping track of the sequence of blocks allocated to each file. With contiguous allocation, the linked list is out of a job, as only the first block and size (or last block) need to be kept for each file, and the FAT essentially turns into a bit map (the details are a bit more messy, but details weren't required).
Most answers to this question were correct.
Block allocation minimizes the data shifting to only the extra blocks needed to hold the new data, plus possibly the old blocks on either side of the new blocks. Contiguous allocation may require data shifting that ripples throughout the file.
Most answers to this question were correct.
The file pointer is the location within the file where reads and writes take
place. Without a file pointer, reads and writes will have to indicate
explicitly the locations within the file where I-O will take place, which is
most easily done by adding a file-location parameter to read() and
write(). Any lseek()-like system calls that manipulate the file pointer
can be deleted,
Most of the answers to this question were wrong, because they confused the
concept of a file pointer with the type FILE * (which we never covered in
class or in the text); the part about system calls in the question should have
been the tip-off that the first version of file pointer was what was meant.
This page last modified on 15 December 2003.