I/O SYSTEMS

1.What are the allocation methods of a disk space?

Methods of allocating disk space which are widely in use are

a.  Contiguous allocation

b.  Linked allocation

c.  Indexed allocation

2.What are the advantages of Contiguous allocation?

The advantages are

a.  Supports direct access

b.  Supports sequential access

c.  Number of disk seeks is minimal.

3.What are the drawbacks of contiguous allocation of disk space?

The disadvantages are

a.  Suffers from external fragmentation

b.  Suffers from internal fragmentation

c.  Difficulty in finding space for a new file

d. File cannot be extended

e.  Size of the file is to be declared in advance

4.What are the advantages of Linked allocation?

The advantages are

a.  No external fragmentation

b.  Size of the file does not need to be declared

5.What are the disadvantages of linked allocation?

The disadvantages are

a.  Used only for sequential access of files.

b.  Direct access is not supported

c.  Memory space required for the pointers.

d. Reliability is compromised if the pointers are lost or damaged

6.What are the advantages of Indexed allocation?

The advantages are

a.  No external-fragmentation problem

b.  Solves the size-declaration problems.

c.  Supports direct access

7.How can the index blocks be implemented in the indexed allocation scheme?

The index block can be implemented as follows 

a. Linked scheme

b.  Multilevel scheme

c.  Combined scheme

8.Define rotational latency and disk bandwidth.

Rotational latency is the additional time waiting for the disk to rotate the desired sector to the disk head. The disk bandwidth is the total number of bytes transferred, divided by the time between the first request for service and the completion of the last transfer.