Free-space management questions test how a file system records available blocks and the overhead of those records. Attempt all 12 before reading the two-sentence explanations, and show every unit conversion in the numerical items.
File allocation asks how a file's blocks are placed; free-space management asks which blocks remain available. KnowledgeGate's File Systems & Allocation MCQs (GATE OS) is the canonical companion for allocation. Question 7 deliberately appears here as a boundary check between placing file blocks and tracking unused blocks.
1. Free Space Management MCQs 1-3: metadata, FAT overhead, and the superblock
Question 1
UP Police 2023, Computer Science, Paper 2 - Subject Oriented (Shift I)
What primary role does the File Control Block (FCB) play in File Management Systems?
A. Encrypts data files
B. Manages user permissions
C. Stores metadata about a file
D. Monitors active database transactions
Correct answer: C. Stores metadata about a file.
An FCB stores metadata for one file, such as its size, access data, timestamps, and block pointers. Encryption and database transactions are separate concerns.
Question 2
Suppose a computer has a file system for a 128 GB disk, where each disk block is 8 KB. If the OS for this computer uses a FAT, what is the smallest amount of memory that could possibly be used for the FAT, assuming the entire FAT is in memory?
A. 48 MB
B. 16 MB
C. 8 MB
D. 32 MB
Using the question's binary-unit convention, the disk has 2^37 / 2^13 = 2^24 blocks, so the FAT needs 2^24 entries. A minimum 24-bit, or 3-byte, entry gives 2^24 x 3 bytes = 48 MB.
Question 3
UGC NET June 2014
_________ maintains the list of free disk blocks in the Unix file system.
A. I-node
B. Boot block
C. Super block
D. File allocation table
Correct answer: C. Super block.
In the classic UNIX model tested here, the superblock holds file-system-wide control data, including free-space information. An i-node describes one file, while the boot block and FAT serve different roles.
2. Free Space Management MCQs 4-5: bitmap size and occupancy
Question 4
UGC NET December 2013
How much space will be required to store the bit map of a 1.3 GB disk with 512 bytes block size ?
A. 332.8 KB
B. 83.6 KB
C. 266.2 KB
D. 256.6 KB
Blocks = (1.3 x 2^30) / 512 = 1.3 x 2^21. One bit per block makes the bitmap (1.3 x 2^21) / (8 x 1024) = 332.8 KB.
Question 5
ISRO 2018
A particular disk unit uses a bit string to record the occupancy or vacancy of its tracks, with 0 denoting vacant and 1 for occupied. A 32-bit segment of this string has hexadecimal value D4FE2003. The percentage of occupied tracks for the corresponding part of the disk, to the nearest percentage is
A. 12
B. 25
C. 38
D. 44
The hexadecimal digits D, 4, F, E, 2, 0, 0, 3 contain 3 + 1 + 4 + 3 + 1 + 0 + 0 + 2 = 14 set bits. Thus 14/32 x 100 = 43.75%, which rounds to 44%.
3. Free Space Management MCQs 6-7: layers and the allocation boundary
Question 6
UGC NET June 2025
Which of the followings shows the correct hierarchy of a layered file system in an operating system?
A. Logical File System
B. File Organization Module
C. Basic File System
D. I/O Control
E. Application Programs
Choose the correct answer from the options given below:
A. A → B → C → D → E
B. D → E → C → A → B
C. E → A → B → C → D
D. E → C → B → A → D
Correct answer: C. E → A → B → C → D.
Requests move from applications to the logical file system, file-organisation module, basic file system, and I/O control. Therefore the order is E, A, B, C, D.
Question 7
GATE 2008
The data blocks of a very large file in the Unix file system are allocated using
A. contiguous allocation
B. linked allocation
C. indexed allocation
D. an extension of indexed allocation
Correct answer: D. an extension of indexed allocation.
A UNIX i-node extends indexed allocation through single-, double-, and triple-indirect pointers when direct entries are insufficient. This tests file-block placement, the boundary identified in the companion link, rather than a free-space data structure.
4. Free Space Management MCQs 8-10: open counts, paths, and space management
Question 8
KVS 2018
File operations that manipulate the ‘open-count’ maintained for each entry in open-file table include _____.
A. open, write
B. read, write
C. write, close
D. open, close
Correct answer: D. open, close.
Open-count tracks active opens represented by an open-file-table entry. A successful open increments it and the matching close decrements it; reads and writes do neither.
Question 9
KVS 2013
This begins at the root and follows a path down to the specified file, giving the directory names on the path. This is known as
A. Absolute path name
B. Relative path name
C. Definite path name
D. Indefinite path name
Correct answer: A. Absolute path name.
/home/asha/os/notes.txt starts at root and gives the full directory chain, so it is absolute. os/notes.txt depends on the current directory and is relative.
Question 10
The part of the file management system which is responsible for managing space on the disk is called:
A. Directory Management
B. File Control Block
C. Space Management
D. File Allocation Table
Correct answer: C. Space Management.
Space management tracks available blocks, allocates them, and records released blocks as free again. Directory management, FCBs, and a particular FAT are different concepts.
5. Free Space Management MCQs 11-12: bitmap states and free-list counting
Question 11
How does the bit-vector method manage free disk space?
A. By tracking free and allocated blocks using 1s and 0s
B. By linking free blocks together
C. By creating an index of all free blocks
D. By maintaining a list of contiguous free blocks
Correct answer: A. By tracking free and allocated blocks using 1s and 0s.
A bit vector assigns one bit to every disk block. Under the stated convention, 1 marks allocated and 0 marks free; linked lists and grouping use different records.
Question 12
UGC NET December 2014
Assume binary units (1 GiB = 2^30 bytes and 1 KiB = 2^10 bytes). A 16 GiB disk uses 1 KiB blocks. To store a linked list that contains one 32-bit number for every disk block, each list block reserves one of its 32-bit slots for the pointer to the next list block. How many list blocks are required?
A. 65,794 blocks
B. 65,536 blocks
C. 20,000 blocks
D. 1,048,576 blocks
Correct answer: A. 65,794 blocks.
The disk contains 2^24 blocks. Each 1 KiB list block has 256 four-byte slots, but one stores the next pointer, so it holds 255 block numbers; ceil(16,777,216 / 255) = 65,794.
6. Diagnose the misses and choose the next practice step
Questions 1 to 3 test metadata and tracking overhead; Questions 4 and 5 test bitmap arithmetic. Questions 6 to 10 cover file-system boundaries and operations, while Questions 11 and 12 contrast bitmap state with free-list counting.
Redo all 12 tomorrow in 10 minutes, allowing 3 minutes for Questions 4 and 5 together. Exam-focused readers can continue with GATE Guidance by Sanchit Sir, placement-focused readers with CS Fundamentals for Placements, and browsers with GATE CS Exam Preparation.
