= Solution
A traditional <inode> uses a fixed number of direct pointers to <file data blocks>, followed by singly, doubly and sometimes triply <indirect block pointers>. A singly <indirect block pointer> reaches one address block whose entries point to <file data blocks>. A doubly <indirect block pointer> reaches a block of pointers to singly indirect address blocks; a triply indirect one adds another level. The <file data blocks> need not be physically contiguous.
This <multilevel inode indexing> keeps the <inode> compact. A small <file> uses direct pointers without allocating address blocks, while a large <file> allocates deeper address blocks only as needed. If each address block holds $q$ addresses, the successive levels cover $q,q^2,q^3$ <file data blocks>. The logical <file offset> selects a path arithmetically, so random access does not require walking through all preceding <file data blocks>.
$$
\boxed{\text{small files: direct access; large files: additional indirection levels}.}
$$
Back to article page
