PREPARATION GUIDE
How To Prepare
Computer Science
Complete preparation strategy for all 10 subjects of Test II — Data Structures, OS, Algorithms, Networks, DBMS, COA, Digital Electronics, TOC, Discrete Math & Compilers.
Preparation Strategy
70 questions across 10 subjects — ~7 questions each. Breadth over depth is the key.
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Critical Rule: BITS HD CS covers MORE topics than GATE CS 2026. Microprocessors (8085/8086), Network Security, Object-Oriented Data Models, and NP-Completeness are in BITS but NOT in GATE. Don’t skip these extras.
01
Phase 1: High PYQ Subjects
Data Structures, Operating Systems, COA
48 BITS PYQs combined. AVL trees, page replacement, CPU scheduling, pipelining, cache memory. These 3 subjects alone are 21 questions.
02
Phase 2: Theory & Memory-Heavy
Computer Networks, DBMS, Discrete Math
44 BITS PYQs. Subnetting, normalization, propositional logic. Lots of formulas — maintain a formula sheet.
03
Phase 3: Problem-Solving Subjects
Algorithms, TOC, Digital Electronics
32 BITS PYQs. Time complexity, DFA/NFA, undecidability, K-maps, MUX. Practice problems daily.
04
Phase 4: Revision & PYQs
Compiler Construction + Full Revision
Solve ALL BITS HD PYQs (128 questions) and relevant GATE PYQs (3000+). Focus on weak areas.
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Time Management: 105 minutes for 70 questions = 1.5 min/question. CS questions are concept-based, not lengthy calculations. Spend 45-60 seconds per question. If stuck beyond 90 seconds, skip and return.
01 Foundational Subjects
42 BITS PYQs | Highest Impact
1. Data Structures
Must Know — ~7 Qs, 17 BITS PYQs, GATE V2: 236 Qs
Most frequently asked subject in BITS HD! Focus on AVL trees, hashing, tree traversals, and stack/queue operations.
ADTs
Algorithm Analysis
Sorting
Searching
Linear Structures
Hash Tables
Search Trees
Height Balancing
Trees
Graphs
Partially Ordered Data
Key Topics & PYQ Patterns
AVL Trees
Min internal nodes for height h: N(h)=N(h-1)+N(h-2)+1. Balance factor ≤ 1. Rotations: LL, RR, LR, RL.
BITS PYQ: AVL rotation type identification and node count by height.
Hashing
Load factor = n/m. BITS PYQ: h=k%9 with linear chaining. Max linked list length? → 4
Collision resolution: separate chaining, linear/quadratic probing, double hashing.
Tree Traversals
Inorder+Preorder OR Inorder+Postorder → unique tree. BST Inorder = sorted.
BITS PYQ: Given two traversals, find the unique tree.
Stack/Queue
Circular queue overflow: (rear+1)%size==front. Stack reverses data stream.
BITS PYQ: Queue state after a sequence of enqueue/dequeue operations.
2. Operating Systems
Must Know — ~7 Qs, 16 BITS PYQs, GATE V2: 335 Qs
Second most asked! Page replacement, CPU scheduling, deadlock, and process synchronization are the high-frequency topics.
Processes
Threads
Scheduling
Concurrency
Mutual Exclusion
Deadlock
Paging
Segmentation
Virtual Memory
Page Replacement
Thrashing
File Systems
I/O
Key Topics & PYQ Patterns
Page Replacement
FIFO: replace oldest. LRU: replace least recently used. Trace page faults step by step.
BITS PYQ: Given a reference string, count FIFO vs LRU page faults.
CPU Scheduling
Waiting Time = Turnaround - Burst. SJF non-preemptive, SRTF preemptive SJF.
BITS PYQ: FCFS, SJF, and RR scheduling — calculate waiting time.
Deadlock
4 conditions: Mutual Exclusion, Hold & Wait, No Preemption, Circular Wait. Break ANY one to prevent.
BITS PYQ: Banker’s algorithm — find safe sequence.
Process Sync
With interleaving: max = sum of increments, min = -(sum of decrements).
BITS PYQ: Two threads incrementing/decrementing a shared variable, find final range.
3. Computer Organization & Architecture
Must Know — ~7 Qs, 15 BITS PYQs, GATE V2: 238 Qs
Pipelining and cache memory are the most tested topics. Master tag bit calculations and speedup formulas.
RISC & CISC
Computer Arithmetic
Control Unit
Cache Memory
Main Memory
I/O
RAID
Pipelining
Instruction-Level Parallelism
Buses
Key Topics & PYQ Patterns
Pipelining
Ideal CPI = 1. Speedup = k (ideal). Hazards: structural, data, control.
BITS PYQ: Speedup with stalls due to data hazards.
Cache
Tag = Total addr bits - Index bits - Offset bits. BITS PYQ: 4-way set assoc, find tag bits.
Direct mapped, set associative, fully associative — know all three.
Address Space
256 TB = 248 bytes → 48 bits. N bytes needs log2(N) bits.
BITS PYQ: Given memory size in TB, find address bus width.
2's Complement
n-bit range: -2(n-1) to 2(n-1)-1. Overflow when sign changes unexpectedly.
BITS PYQ: Overflow detection in signed addition.
02 Networking & Data
26 BITS PYQs
4. Computer Networks
Must Know — ~7 Qs, 14 BITS PYQs, GATE V2: 215 Qs
Subnetting, TCP/UDP, and HTTP are the core. BITS also tests WiFi, Network Security, and Multicast Routing — topics NOT in GATE CS 2026.
LAN/MAN/WAN
IEEE 802
Ethernet
WiFi 802.11
IPv4
IPv6
Subnetting
RIP
OSPF
BGP
TCP
UDP
HTTP
DNS
DHCP
SMTP
Cryptography
Firewalls
IDS
Key Topics & PYQ Patterns
Subnetting
Subnet ID = IP AND mask. Broadcast = subnet ID OR (~mask). CIDR /24 = 24 network bits.
BITS PYQ: Given IP and subnet mask, find subnet ID and broadcast.
TCP/UDP
HTTP:80, HTTPS:443, FTP:21, SSH:22, DNS:53, SMTP:25. UDP max: 65535 bytes.
BITS PYQ: Well-known port numbers and protocol identification.
HTTP 1.0 vs 1.1
HTTP 1.1 = persistent (single TCP reused). 1.0 = non-persistent (new per object).
BITS PYQ: Object download time comparison for persistent vs non-persistent.
Sliding Window
Go-Back-N: W ≤ 2n - 1. Selective Repeat: W ≤ 2(n-1).
BITS PYQ: Given sequence number bits, find max window size.
5. Database Systems
Must Know — ~7 Qs, 12 BITS PYQs, GATE V2: 284 Qs
Normalization is the most tested topic. Also focus on SQL joins, ER modeling, and transaction management (2PL).
ER Model
Relational Model
O-O Model
Object-Relational
Relational Algebra
SQL
Normalization
FDs
BCNF
4NF
Indexing
Query Optimization
Transactions
2PL
Crash Recovery
Key Topics & PYQ Patterns
Normalization
BCNF: every determinant is candidate key. BCNF guarantees ZERO redundancy.
BITS PYQ: Find highest normal form given FDs and candidate keys.
SQL Joins
Valid: INNER, LEFT, RIGHT, FULL OUTER, CROSS. PRODUCT and UNION are NOT join types.
BITS PYQ: Identify valid SQL join type from options.
Transactions
Strict 2PL: holds locks until commit. Wait-Die: older waits, younger dies.
BITS PYQ: Deadlock detection in wait-for graph.
Schema Levels
3 levels: External (user view), Logical/Conceptual, Internal/Physical (storage).
BITS PYQ: Data independence types — logical vs physical.
03 Algorithms & Theory
18 BITS PYQs
6. Discrete Mathematics
Must Know — ~7 Qs, 18 BITS PYQs, GATE V1: 381 Qs
Highest BITS PYQ count! Combinatorics, functions/relations, and propositional logic. All topics overlap with GATE — no extra study needed.
Counting
Recurrence Relations
Sets
Functions
Relations
Propositional Logic
Predicate Logic
Strings
Languages
Key Topics & PYQ Patterns
Combinatorics
nCr, nPr, circular: (n-1)!. BITS PYQ: 8-bit strings with 5 ones? = C(8,5)=56
Pigeonhole, stars and bars, inclusion-exclusion.
Functions
1-1 functions from {A,B,C} to {1,2,3}? = 3! = 6. Total relations A×B: 2(|A|×|B|)
BITS PYQ: Count injective, surjective, bijective functions.
Logic
Truth tables, tautology, contradiction. Graphs: sum of degrees = 2|E|, odd-degree vertices always even.
BITS PYQ: Is a formula a tautology? Evaluate propositional logic.
7. Design & Analysis of Algorithms
Must Know — ~7 Qs, 10 BITS PYQs, GATE V2: 334 Qs
BITS syllabus has EXTRA topics not in GATE 2026: Randomization, NP-Completeness, Backtracking, Branch-and-Bound, Approximation Algorithms. Don’t skip these!
Divide & Conquer
Greedy
Dynamic Programming
Randomization
Complexity Analysis
Master Theorem
Lower Bounds
NP-Completeness
NP-Hardness
Reductions
Backtracking
Branch-and-Bound
Approximation
Key Topics & PYQ Patterns
Master Theorem
T(n)=aT(n/b)+f(n). BITS PYQ: T(n)=2T(n1/2)+log n
Case 1: f(n) = O(nlogba - e). Case 2: f(n) = Θ(nlogba logkn). Case 3: f(n) = Ω(nlogba + e).
Sorting
Stable: Merge, Insertion, Bubble. Unstable: Quick, Heap, Selection.
BITS PYQ: Which sorting is stable? Lower bound of comparison sort: O(n log n).
Graph Algorithms
DFS/BFS: O(V+E) with adj list. BITS PYQ: DFS on complete graph using adj list? = O(V2)
Dijkstra, Bellman-Ford, Floyd-Warshall, Kruskal, Prim.
NP-Completeness
TSP paths: (n-1)!/2. Recursive uses MORE space than iterative.
BITS PYQ: NP-Completeness reductions — SAT, 3-COLORING, CLIQUE.
8. Theory of Computation
Must Know — ~7 Qs, 8 BITS PYQs, GATE V2: 286 Qs
DFA/NFA, CFG closure properties, and undecidability are the key areas. Rice’s Theorem is heavily tested.
Regular Languages
Regular Expressions
DFA
NFA
CFG
CFL
PDA
Pumping Lemma
Turing Machines
Universal TM
Recursive Languages
RE Languages
Decidability
Key Topics & PYQ Patterns
DFA/NFA
Minimal DFA for a*b* has 2 states. NFA→DFA can have up to 2n states.
BITS PYQ: Count states in minimal DFA for a given language.
CFL Closure
CFL closed under: union, concatenation, Kleene star, reverse. NOT closed under: intersection, complement.
BITS PYQ: Is CFL closed under intersection? No!
Undecidability
For TM: Is L(M) empty/finite/regular/CFL? ALL undecidable. For DFA/CFG: emptiness IS decidable.
BITS PYQ: Rice’s Theorem — non-trivial semantic properties of TM are undecidable.
Pumping Lemma
anbn = CFL (not regular). anbncn = not CFL.
BITS PYQ: Use pumping lemma to prove a language is not regular.
04 Hardware & Systems
18 BITS PYQs
9. Digital Electronics & Microprocessors
Must Know — ~7 Qs, 14 BITS PYQs, GATE V2: 303 Qs
BITS tests 8085/8086 microprocessors — NOT in GATE CS 2026. Also focus on K-maps, MUX, and flip-flops.
Adders
MUX
DeMUX
Encoders
Decoders
Counters
Registers
PLDs
Logic Families
K-Maps
8085
8086
Memory Interfacing
8253
8255
8259
8251
Key Topics & PYQ Patterns
K-Maps
Group 1s for SOP, group 0s for POS. Simplify boolean expressions.
BITS PYQ: Given minterms, simplify using K-map.
MUX
2n inputs, n select lines, 1 output. Can implement any boolean function.
BITS PYQ: Given select lines and data, find output.
Flip-Flop vs Latch
KEY: Latch = level-triggered. Flip-Flop = edge-triggered (changes ONLY on clock edge).
BITS PYQ: Race-around condition in JK flip-flop if T > pulse width.
8085/8086
HLT: stop until interrupt. HOLD: DMA bus request. 8259 cascaded needs ICW1, ICW2, ICW3.
BITS PYQ: 8085 addressing modes, 8086 segmentation.
10. Compiler Construction
Important — ~7 Qs, 4 BITS PYQs, GATE V2: 234 Qs
Lowest PYQ count but still 7 questions on the exam! Focus on compiler phases, CFG/parsing basics, and semantic analysis.
Lexical Analysis
Parsing
Top-Down
Bottom-Up
Abstract Syntax Tree
Symbol Tables
Semantic Analysis
Type Checking
Syntax Directed Translation
Intermediate Code
Code Generation
Register Allocation
Key Topics & PYQ Patterns
Phases
Lexical→Syntax→Semantic→Intermediate Code→Optimization→Code Gen. Every CHARACTER seen in: Lexical Analysis.
BITS PYQ: Which phase handles character-level scanning?
Grammar
CFG = syntax. Attribute Grammar = semantics AND syntax. Type checker = semantic phase.
BITS PYQ: Attribute grammars and inherited vs synthesized attributes.
Parsing
LL = top-down, LR = bottom-up (more powerful). FIRST/FOLLOW sets.
BITS PYQ: Compute FIRST and FOLLOW sets for a given grammar.
Final Tips for Computer Science
70 questions in 105 minutes — every subject matters equally.
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Scoring Strategy:
• Data Structures, OS, COA = 21 questions, highest PYQ frequency. Master these 3 first.
• Don’t skip “extra” topics — Microprocessors, Network Security, NP-Completeness appear in BITS but NOT in GATE.
• Maintain a formula sheet: cache tag bits, page replacement traces, subnetting, normalization rules.
• Time: 1.5 min/question. Concept-based, not calculation-heavy. If stuck >90 sec, skip.
• Solve ALL 128 BITS HD PYQs — many questions repeat in spirit.
- Breadth over Depth — cover all 10 subjects superficially rather than mastering 5. Subject weightage is volatile.
- PYQs are gold — BITS HD has 128 CS PYQs available. Solve them topic-by-topic after completing each subject.
- GATE PYQs (Volume 2) — 3000+ CS questions. Use for practice, not just GATE prep.
- Formula sheet is essential — cache tag bits, deadlock conditions, CFL closure properties, sliding window sizes.
- Microprocessors need extra study — 8085/8086 architecture and assembly are NOT in GATE. Use Morris Mano or online resources.
- Network Security basics — Cryptography, digital signatures, IDS, firewalls. These appear in BITS but not GATE CS 2026.
- Marking: +3/-1/0 — if unsure between 2 options, attempt. If no idea at all, SKIP.
Recommended Books & Resources
These textbooks + GATE PYQs cover everything. No need for paid courses.