Indexed/grouped allocation is useful as :

(A) It supports both sequential and direct access.

(B) Entire block is available for data.

(C) It does not require lots of space for keeping pointers.

(D) No external fragmentation.

Choose the correct answer from the options given below:

The correct answer is (A), (B) and (D) Only

EXPLANATION:

• (A) It supports both sequential and direct access.
  • Indexed/grouped allocation allows both sequential (one block after another) and direct (jumping straight to a desired block) access to data.
• (B) Entire block is available for data.
  • In indexed allocation, the entire block is indeed available for storing data. The index block, a separate entity, contains the pointers to the data blocks.
• (D) No external fragmentation.
  • Indexed allocation helps prevent external fragmentation as all files have their own index block that keeps track of the blocks associated with it.

However, option (C) is not correct because indexed allocation actually needs space to store pointers in the index block for each file, which can be considerably large for large files. Therefore, indexed allocation does require lots of space for keeping pointers.