What are common examiner traps in File Systems?

Neglecting per-sector transfer time (Ttrans) when computing total access time for random reads unless explicitly stated as negligible. Confusing base-10 metrics (MB = 106 bytes) with binary metrics (MiB = 220 bytes); always follow problem specifications. Forgetting to subtract pointer sizes (e.g., 4 bytes for next pointer) from block capacity when computing usable data capacity in linked allocation. Ceiling vs floor errors when calculating the number of blocks needed to hold remaining file fragments or free lists. Assuming deletion/opening in linear directory lists requires a full scan; full scan is strictly required when verifying uniqueness (creation/renaming). Failing to account for read-and-write cycles when shifting blocks during insertions in contiguous allocation.

File Systems

14 Qs · since 2011 · 24 marks · 1 marks/paperStandard yield

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File systems and secondary storage in GATE CS are predominantly tested through numerical calculation problems (NAT/MCQ) involving disk geometry, timing analysis, and block allocati… Guide

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GATE CSE 2026 Set 1Q59NAT2 marksMediumConsider a hard disk with a rotational speed of 15000 rpm. The time to move the read/write head from a track to its adjacent track is 1 millisecond. Initially, the head is on track 0. The number of sectors per track is 400. The sector size is 1024 bytes. It is necessary to transfer data from 10 randomly located…
GATE CSE 2026 Set 2Q53NAT2 marksMediumTo keep track of free blocks in a file system, one of the two approaches is generally used – using bitmaps (bit vectors) or using linked lists. Consider that the linked list approach is used to keep track of free blocks in a file system. Assume that the disk size is 16 GB, block size is 2 KB, and block numbers used…
GATE CSE 2025 Set 1Q51NAT2 marksMediumA disk of size 512M bytes is divided into blocks of 64K bytes. A file is stored in the disk using linked allocation. In linked allocation, each data block reserves 4 bytes to store the pointer to the next data block. The link part of the last data block contains a $NULL$ pointer (also of 4 bytes). Suppose a file of…
GATE CSE 2024 Set 2Q53NAT2 marksMediumConsider a disk with the following specifications: rotation speed of 6000 RPM, average seek time of 5 milliseconds, 500 sectors/track, 512-byte sectors. A file has content stored in 3000 sectors located $\textit{randomly}$ on the disk. Assuming average rotational latency, the total time ( $\textit{in seconds, rounded off to 2 decimal places}$ …
GATE CSE 2022Q63NAT2 marksMediumConsider two files systems $A$ and $B$ , that use contiguous allocation and linked allocation, respectively. A file of size 100 blocks is already stored in A and also in B. Now, consider inserting a new block in the middle of the file (between $50^{\text{th}}$ and $51^{\text{st}}$ block), whose data is already…
GATE CSE 2021 Set 1Q15MSQ1 markMediumConsider a linear list based directory implementation in a file system. Each directory is a list of nodes, where each node contains the file name along with the file metadata, such as the list of pointers to the data blocks. Consider a given directory foo. Which of the following operations will…
GATE CSE 2017 Set 2Q8MCQ1 markEasyIn a file allocation system, which of the following allocation scheme(s) can be used if no external fragmentation is allowed? I. Contiguous II. Linked III. Indexed
GATE CSE 2016 Set 2Q50NAT2 marksMediumDiagramA file system uses an in-memory cache to cache disk blocks. The miss rate of the cache is shown in the figure. The latency to read a block from the cache is 1 ms and to read a block from the disk is 10 ms. Assume that the cost of checking whether a block exists in the cache is negligible. Available cache sizes are in…
GATE CSE 2015 Set 1Q48NAT2 marksMediumConsider a disk pack with a seek time of 4 milliseconds and rotational speed of 10000 rotations per minute (RPM). It has 600 sectors per track and each sector can store 512 bytes of data. Consider a file stored in the disk. The file contains 2000 sectors. Assume that every sector access necessitates a seek, and the…
GATE CSE 2014 Set 1Q19NAT1 markEasySuppose a disk has 201 cylinders, numbered from 0 to 200. At some time the disk arm is at cylinder 100, and there is a queue of disk access requests for cylinders 30, 85, 90, 100, 105, 110, 135 and 145. If Shortest-Seek Time First (SSTF) is being used for scheduling the disk access, the request for cylinder 90 is…
GATE CSE 2014 Set 2Q20NAT1 markMediumA FAT (file allocation table) based file system is being used and the total overhead of each entry in the FAT is 4 bytes in size. Given a $100 \times 10^6$ bytes disk on which the file system is stored and data block size is $10^3$ bytes, the maximum size of a file that can be stored on this disk in units of $10^6$ …
GATE CSE 2013Q29MCQ2 marksMediumConsider a hard disk with 16 recording surfaces (0-15) having 16384 cylinders (0-16383) and each cylinder contains 64 sectors (0-63). Data storage capacity in each sector is 512 bytes. Data are organized cylinder-wise and the addressing format is $\langle\text{cylinder no., surface no., sector no.}\rangle$ . A file…
GATE CSE 2012Q41MCQ2 marksMediumA file system with 300 GByte disk uses a file descriptor with 8 direct block addresses, 1 indirect block address and 1 doubly indirect block address. The size of each disk block is 128 Bytes and the size of each disk block address is 8 Bytes. The maximum possible file size in this file system is
GATE CSE 2011Q44MCQ2 marksEasyAn application loads 100 libraries at startup. Loading each library requires exactly one disk access. The seek time of the disk to a random location is given as 10 ms. Rotational speed of disk is 6000 rpm. If all 100 libraries are loaded from random locations on the disk, how long does it take to load all libraries?…

Topic guide

What does GATE test in File Systems?

File systems and secondary storage in GATE CS are predominantly tested through numerical calculation problems (NAT/MCQ) involving disk geometry, timing analysis, and block allocation schemes. The questions focus on low-level mechanics: rotational latency, seek time, track transfer overhead, inode/FAT/linked pointer calculations, free space management, and disk scheduling algorithms. A smaller subset tests conceptual directory operations and allocation fragmentation properties.

Core concepts

Magnetic disk geometry: Platters, surfaces, cylinders, tracks, and sectors
Disk access time components: Seek time, rotational latency, and transfer time
Disk scheduling policies: FCFS, SSTF, SCAN, C-SCAN, LOOK, C-LOOK
File allocation methods: Contiguous, Linked list, FAT, and Multi-level Indexed (inode)
Directory representations: Linear list vs hash table and operational complexity (create, delete, rename, open)
Free-space management: Bitmaps (bit vectors), Linked lists, and Grouping/Counting
Internal and External fragmentation in secondary storage allocation
Disk block caching and average read/write latency

Recurring question patterns

Magnetic Disk Timing & Access Calculation
common · NAT · 2 marks · 2026, 2024, 2015, 2011
Given rotational speed (RPM), seek time (fixed or per track distance), sector count per track, and sector size, compute the total access/transfer time to read randomly located sectors or contiguous blocks across multiple cylinders/tracks.
File Allocation Data Structure Overhead & Capacity
common · NAT · 2 marks · 2026, 2025, 2014, 2012
Calculations involving file system data structures like direct/single/double indirect pointers (UNIX inode-style), File Allocation Tables (FAT), or linked allocations with embedded pointers to find maximum file size, internal fragmentation, or metadata table size.
Disk Head Scheduling and Traversal
occasional · NAT · 1 marks · 2014
Evaluating disk scheduling algorithms (SSTF, FCFS, SCAN, C-SCAN, LOOK) given an initial head position and a queue of cylinder requests to determine total head movements or the service order of a specific request.
Contiguous Addressing & Sector Mapping
occasional · MCQ · 2 marks · 2013
Mapping multi-dimensional cylinder/surface/sector tuples into linear disk offsets or determining the final sector/cylinder coordinates for a file stored contiguously.
File Allocation & Directory Operations Conceptual
common · mixed · 1.5 marks · 2022, 2021, 2017
Comparing properties of file allocation schemes (Contiguous, Linked, Indexed) regarding fragmentation, disk read/write costs for modifications (insertion/deletion), or linear directory search requirements.

Formulas GATE uses

Rotation Time and Latency

T_{\text{rot}} = \frac{60}{\text{RPM}} \text{ s}, \quad T_{\text{lat}} = \frac{T_{\text{rot}}}{2}

Used to find the time for one full disk revolution and average rotational latency.

Sector Transfer Time

T_{\text{trans}} = \frac{T_{\text{rot}}}{\text{Sectors per Track}}

Used when computing the precise transfer time for a single sector.

Total Disk Access Time per Random Sector

T_{\text{access}} = T_{\text{seek}} + T_{\text{lat}} + T_{\text{trans}}

Used to compute total file access time across $N$ independently/randomly placed sectors.

Index Block Capacity (Indirect Addressing)

N_{\text{ptrs}} = \left\lfloor \frac{\text{Block Size}}{\text{Pointer Size}} \right\rfloor

Used to find addressable data blocks from single, double, or triple indirect pointers.

Free List Block Capacity

N_{\text{entries}} = \left\lfloor \frac{\text{Block Size} - \text{Link Pointer Size}}{\text{Block Number Size}} \right\rfloor

Used to determine how many free block IDs fit into linked free list blocks.

Average Memory/Disk Access Time with Cache

T_{\text{avg}} = (1 - m) T_{\text{cache}} + m T_{\text{disk}}

Used to calculate required cache miss rates or target latencies for in-memory block caches.

Examiner traps in File Systems

Neglecting per-sector transfer time (Ttrans) when computing total access time for random reads unless explicitly stated as negligible.
Confusing base-10 metrics (MB = 106 bytes) with binary metrics (MiB = 220 bytes); always follow problem specifications.
Forgetting to subtract pointer sizes (e.g., 4 bytes for next pointer) from block capacity when computing usable data capacity in linked allocation.
Ceiling vs floor errors when calculating the number of blocks needed to hold remaining file fragments or free lists.
Assuming deletion/opening in linear directory lists requires a full scan; full scan is strictly required when verifying uniqueness (creation/renaming).
Failing to account for read-and-write cycles when shifting blocks during insertions in contiguous allocation.

How questions are asked

Compute total access/read time given RPM, seek time, track layout, and number of random/contiguous sectors
Compute maximum file size supported by an inode / multilevel index configuration
Determine number of blocks or bytes lost to internal/external fragmentation
Calculate disk head movements or request service count in SSTF / SCAN scheduling
Find number of blocks required to store free lists or FAT overhead
Conceptual MSQ on directory traversal overheads or allocation scheme tradeoffs

Paper trends

Shift from simple single-step MCQs to multi-step NAT questions requiring exact arithmetic with conversions between SI decimal ( $10^6$ ) and binary units ( $2^{10}, 2^{20}$ ).
2026, 2025, 2024, 2014
Increased focus on detailed memory/block-level pointer accounting (such as linking overhead per data block, free block numbering structures, and internal fragmentation byte calculations).
2026, 2025, 2022
Introduction of MSQ and multi-criteria questions to test operational implications of directory implementations and file allocation schemes.
2021

Difficulty notes

Easy questions are straightforward disk scheduling steps (SSTF order) or 1-step rotational latency formulas. Medium questions involve multi-stage calculations such as chained track seek sequences, inode multilevel pointer tree summation, linked allocation internal fragmentation arithmetic, or free-space block sizing with sub-byte or boundary conversions.

File Systems

14 Qs · since 2011 · 24 marks · 1 marks/paperStandard yield

Take topic test

File systems and secondary storage in GATE CS are predominantly tested through numerical calculation problems (NAT/MCQ) involving disk geometry, timing analysis, and block allocati… Guide

Type

Topic guide

What does GATE test in File Systems?

Core concepts

Magnetic disk geometry: Platters, surfaces, cylinders, tracks, and sectors
Disk access time components: Seek time, rotational latency, and transfer time
Disk scheduling policies: FCFS, SSTF, SCAN, C-SCAN, LOOK, C-LOOK
File allocation methods: Contiguous, Linked list, FAT, and Multi-level Indexed (inode)
Directory representations: Linear list vs hash table and operational complexity (create, delete, rename, open)
Free-space management: Bitmaps (bit vectors), Linked lists, and Grouping/Counting
Internal and External fragmentation in secondary storage allocation
Disk block caching and average read/write latency

Recurring question patterns

Magnetic Disk Timing & Access Calculation
common · NAT · 2 marks · 2026, 2024, 2015, 2011
Given rotational speed (RPM), seek time (fixed or per track distance), sector count per track, and sector size, compute the total access/transfer time to read randomly located sectors or contiguous blocks across multiple cylinders/tracks.
File Allocation Data Structure Overhead & Capacity
common · NAT · 2 marks · 2026, 2025, 2014, 2012
Calculations involving file system data structures like direct/single/double indirect pointers (UNIX inode-style), File Allocation Tables (FAT), or linked allocations with embedded pointers to find maximum file size, internal fragmentation, or metadata table size.
Disk Head Scheduling and Traversal
occasional · NAT · 1 marks · 2014
Evaluating disk scheduling algorithms (SSTF, FCFS, SCAN, C-SCAN, LOOK) given an initial head position and a queue of cylinder requests to determine total head movements or the service order of a specific request.
Contiguous Addressing & Sector Mapping
occasional · MCQ · 2 marks · 2013
Mapping multi-dimensional cylinder/surface/sector tuples into linear disk offsets or determining the final sector/cylinder coordinates for a file stored contiguously.
File Allocation & Directory Operations Conceptual
common · mixed · 1.5 marks · 2022, 2021, 2017
Comparing properties of file allocation schemes (Contiguous, Linked, Indexed) regarding fragmentation, disk read/write costs for modifications (insertion/deletion), or linear directory search requirements.

Formulas GATE uses

Rotation Time and Latency

T_{\text{rot}} = \frac{60}{\text{RPM}} \text{ s}, \quad T_{\text{lat}} = \frac{T_{\text{rot}}}{2}

Used to find the time for one full disk revolution and average rotational latency.

Sector Transfer Time

T_{\text{trans}} = \frac{T_{\text{rot}}}{\text{Sectors per Track}}

Used when computing the precise transfer time for a single sector.

Total Disk Access Time per Random Sector

T_{\text{access}} = T_{\text{seek}} + T_{\text{lat}} + T_{\text{trans}}

Used to compute total file access time across $N$ independently/randomly placed sectors.

Index Block Capacity (Indirect Addressing)

N_{\text{ptrs}} = \left\lfloor \frac{\text{Block Size}}{\text{Pointer Size}} \right\rfloor

Used to find addressable data blocks from single, double, or triple indirect pointers.

Free List Block Capacity

N_{\text{entries}} = \left\lfloor \frac{\text{Block Size} - \text{Link Pointer Size}}{\text{Block Number Size}} \right\rfloor

Used to determine how many free block IDs fit into linked free list blocks.

Average Memory/Disk Access Time with Cache

T_{\text{avg}} = (1 - m) T_{\text{cache}} + m T_{\text{disk}}

Used to calculate required cache miss rates or target latencies for in-memory block caches.

Examiner traps in File Systems

Neglecting per-sector transfer time (Ttrans) when computing total access time for random reads unless explicitly stated as negligible.
Confusing base-10 metrics (MB = 106 bytes) with binary metrics (MiB = 220 bytes); always follow problem specifications.
Forgetting to subtract pointer sizes (e.g., 4 bytes for next pointer) from block capacity when computing usable data capacity in linked allocation.
Ceiling vs floor errors when calculating the number of blocks needed to hold remaining file fragments or free lists.
Assuming deletion/opening in linear directory lists requires a full scan; full scan is strictly required when verifying uniqueness (creation/renaming).
Failing to account for read-and-write cycles when shifting blocks during insertions in contiguous allocation.

How questions are asked

Compute total access/read time given RPM, seek time, track layout, and number of random/contiguous sectors
Compute maximum file size supported by an inode / multilevel index configuration
Determine number of blocks or bytes lost to internal/external fragmentation
Calculate disk head movements or request service count in SSTF / SCAN scheduling
Find number of blocks required to store free lists or FAT overhead
Conceptual MSQ on directory traversal overheads or allocation scheme tradeoffs

Paper trends

Shift from simple single-step MCQs to multi-step NAT questions requiring exact arithmetic with conversions between SI decimal ( $10^6$ ) and binary units ( $2^{10}, 2^{20}$ ).
2026, 2025, 2024, 2014
Increased focus on detailed memory/block-level pointer accounting (such as linking overhead per data block, free block numbering structures, and internal fragmentation byte calculations).
2026, 2025, 2022
Introduction of MSQ and multi-criteria questions to test operational implications of directory implementations and file allocation schemes.
2021