Digital Logic for GATE CS 2027: Weightage, PYQs & Study Plan

Digital Logic is worth about 6 to 7 marks per GATE CS paper, or roughly 6.5% of the 100-mark paper, and it is one of the easiest subjects to score in. We counted every Digital Logic question in all 23 official GATE CS papers from 2014 to 2026. It averaged 6.5 marks, ranged from 3 to 9, and has carried 6 to 8 marks in every paper since 2023. Only 5 of its 100 questions are rated hard. Boolean algebra and K-maps are the biggest topic, while number representation (two's complement and IEEE 754) has grown the most. This guide covers the official 2027 syllabus and what changed, topic-by-topic numbers, five worked questions from past papers and a study order.

GATE CS 2027 Digital Logic Syllabus (and What Changed)

Digital Logic is Section 2 of the official GATE 2027 CS syllabus. The official text reads:

• Boolean algebra and minimization: algebraic technique, Karnaugh map, tabular method
• Design of combinational and sequential circuits
• Number representation and arithmetic (fixed and floating point)

The GATE 2026 CS syllabus read "Boolean algebra. Combinational and sequential circuits. Minimization. Number representations and computer arithmetic (fixed and floating point)." The 2027 wording is more specific. It names the three minimisation methods (algebraic, K-map and the tabular, Quine–McCluskey method) and says design of combinational and sequential circuits. The topics are the same, but expect circuit design and tabular-method questions to be fair game. For the full CS syllabus, see our GATE CS syllabus page.

How Many Marks Does Digital Logic Carry in GATE CS?

The official question paper pattern fixes marks only for General Aptitude (15) and Engineering Mathematics (13). This is what Digital Logic carried in each paper:

What this means: Digital Logic has edged up, from 6.2 marks per paper before 2021 to 6.9 after, and the 2025 and 2026 papers all had 7 or 8 marks. It has a short syllabus and a low share of hard questions. That makes it one of the most efficient subjects to master early, and it also prepares you for COA. For how it compares with other subjects, see our GATE CSE subject-wise weightage analysis.

Topic-Wise Weightage: Where Digital Logic Marks Come From

We grouped the 100 Digital Logic questions by syllabus heading, with the average marks per paper across all 23 papers:

Looking at individual topics, the most-asked across all 23 papers were Boolean laws and expression simplification (19 questions, 26 marks), K-map minimisation (13 questions, 24 marks), number base conversions (11 questions), IEEE 754 floating point (10 questions, 15 marks) and counters (10 questions, 16 marks).

Three patterns stand out:

1. Boolean algebra is still the core. At about 2.4 to 2.8 marks per paper, simplifying expressions, minimising with K-maps and counting minterms appear every year.
2. Number representation has grown the most. It rose from 1.6 to 2.2 marks per paper. 2026 asked about sign-magnitude overflow, two's-complement overflow and IEEE 754 decoding, with both sets testing overflow.
3. Sequential circuits are rising. They went from 0.9 to 1.3 marks per paper, mainly counter frequency and state questions, which fits the 2027 syllabus's emphasis on design of sequential circuits.

Question Types in Digital Logic

From 2021 to 2026, the 45 Digital Logic questions split into 19 MCQs, 16 MSQs and 10 NATs, carrying 30, 24 and 15 marks respectively. Overflow and property questions are usually MSQs, where every option has to be checked. Conversions and counter frequencies are usually NATs. A wrong 1-mark MCQ costs 1/3 mark and a wrong 2-mark MCQ costs 2/3 mark. MSQs and NATs carry no negative marks (official marking rules).

Topic by Topic: What GATE Asks and How to Prepare

1. Boolean Algebra and Minimisation

What gets asked: simplifying Boolean expressions, minimal sum-of-products or product-of-sums forms, the number of prime implicants or essential prime implicants, minterm and maxterm conversion, and properties of Boolean algebra.

How to prepare: draw the K-map for every minimisation question with four or fewer variables, and look for wrap-around groups (worked example 4). Learn the definitions of prime and essential prime implicants. The 2027 syllabus names the tabular (Quine–McCluskey) method, so practise one or two by hand. For the algebraic technique, learn consensus, absorption and De Morgan's laws.

Recent PYQs: K-map from minterms (2026, MSQ), two-variable function (2026, MSQ), properties of Boolean algebra (2026).

2. Number Representation and Arithmetic

What gets asked: base conversions, two's-complement, one's-complement and sign-magnitude ranges, overflow detection, IEEE 754 single-precision encoding and decoding, and fixed-point arithmetic.

How to prepare: learn the ranges for n bits. Two's complement covers −2ⁿ⁻¹ to 2ⁿ⁻¹ − 1. Sign-magnitude and one's complement cover −(2ⁿ⁻¹ − 1) to 2ⁿ⁻¹ − 1. For overflow, convert to decimal, compute, and check the result against the range (worked examples 2 and 3). For IEEE 754, value = (−1)^s × 1.mantissa × 2^{exponent − 127} (worked example 1).

Recent PYQs: IEEE 754 variables (2026), sign-magnitude overflow (2026, MSQ).

3. Sequential Circuits

What gets asked: counter outputs and frequencies, ripple versus synchronous counters, flip-flop characteristic tables (JK, T, D), shift registers, and state minimisation of finite state machines.

How to prepare: each flip-flop stage of a ripple counter divides the frequency by 2, so an n-bit counter divides the clock by 2ⁿ (worked example 5). For state-machine questions, build the state table first, then merge equivalent states.

Recent PYQs: saturating up/down counter (2026), FSM state minimisation (2025, NAT), D flip-flop circuit (2025, NAT).

4. Combinational Circuits

What gets asked: functions implemented by multiplexers, decoders and encoders, adders and carry look-ahead, and propagation delay and hazards.

How to prepare: to find what a multiplexer circuit computes, write its output as a sum of products over the select lines and simplify. For delay questions, trace the longest path from input to output.

Recent PYQs: decoder circuit (2026, NAT), three 2-to-1 multiplexers (2024, NAT), gate delays and hazards (2024, MSQ).

Worked Examples from Official GATE CS Papers

Each answer below matches the official answer key, as reproduced on the linked question page.

Example 1: Decoding IEEE 754 (GATE CS 2026 Set 2, Q34, 1 mark, NAT)

Question: what decimal number has the IEEE 754 single-precision representation 0xC2710000?

Solution: in binary this is 1 | 10000100 | 1110001000…. The sign is negative. The exponent is 132 − 127 = 5. The mantissa is 1.1110001₂ = 1 + 0.5 + 0.25 + 0.125 + 0.0078125 = 1.8828125. The value is −1.8828125 × 2⁵ = −60.25. Practise this question.

Example 2: Overflow in sign-magnitude (GATE CS 2026 Set 1, Q22, 1 mark, MSQ)

Question: in 8-bit sign-magnitude, X = 10110100 and Y = 01001100. Which of X + Y, X − Y, −X + Y and −X − Y overflow?

Solution: X = −52, Y = +76, and the range is −127 to +127. X + Y = 24 and −X − Y = −24 fit. X − Y = −128 and −X + Y = +128 do not. The answer is X − Y and −X + Y. Note that −128 overflows here even though it would fit in two's complement. Practise this question.

Example 3: Overflow in two's complement (GATE CS 2026 Set 2, Q28, 1 mark, MSQ)

Question: in 4-bit two's complement, N1 = 1011, N2 = 1101, N3 = 1010 and N4 = 1001. Which of N1 + N2, N2 + N3, N3 − N4 and N1 + N4 overflow?

Solution: N1 = −5, N2 = −3, N3 = −6, N4 = −7, and the range is −8 to +7. N1 + N2 = −8 fits. N2 + N3 = −9 overflows. N3 − N4 = +1 fits. N1 + N4 = −12 overflows. The answer is N2 + N3 and N1 + N4. Practise this question.

Example 4: Minimal SOP (GATE CS 2026 Set 2, Q40, 2 marks)

Question: F(A, B, C, D) = Σm(0, 1, 2, 3, 8, 9, 10, 11). What is the minimal sum of products?

Solution: minterms 0 to 3 are the whole row where A = 0 and B = 0. Minterms 8 to 11 are the whole row where A = 1 and B = 0. Together they form one 8-cell group where B = 0, so F = B′. Practise this question.

Example 5: Ripple counter frequency (GATE CS 2025 Set 2, Q34, 1 mark, NAT)

Question: in a 4-bit ripple counter, the last flip-flop's waveform has a 64 µs period. What is the counter's input frequency in kHz?

Solution: the last stage runs at 1 ÷ 64 µs = 15.625 kHz. Each stage divides by 2, so the input is 15.625 × 2⁴ = 250 kHz. Practise this question.

Study Order and Time Plan

Digital Logic takes roughly 2 to 3 weeks at 2 hours a day. Study it early, because COA builds on it.

1. Number systems and representation (4–5 days): conversions, the complement forms, overflow and IEEE 754.
2. Boolean algebra and minimisation (5 days): laws, K-maps, prime implicants and one pass of the tabular method.
3. Combinational circuits (3 days): multiplexers, decoders, adders and delay.
4. Sequential circuits (4 days): flip-flops, counters, shift registers and state machines.
5. PYQ sweep (2–3 days): all 100 Digital Logic questions from 2014 to 2026 on the GATE CS PYQ archive.

For where Digital Logic fits among all the subjects, see the GATE CSE 2027 month-by-month study plan.

Best Books for GATE CS Digital Logic

For other subjects, see our best books for GATE CSE 2027. The full course, covering all subjects with lectures and mock tests, is on the GATE CS course page.

Common Mistakes in GATE Digital Logic

• Using the two's-complement range for sign-magnitude. Sign-magnitude cannot represent −2ⁿ⁻¹ (Example 2).
• Forgetting the 127 bias or the implicit leading 1 in IEEE 754 (Example 1).
• Missing wrap-around groups on a K-map (Example 4).
• Treating a ripple counter as synchronous in delay and frequency questions.
• Checking only one option in an overflow MSQ. Compute every option.

Key Takeaways

• Digital Logic averaged 6.5 marks per paper (6.5% of the paper) across 23 official GATE CS papers (2014–2026), and 7 to 8 marks in 2025 and 2026.
• Boolean algebra and minimisation is the biggest topic (61 marks). Number representation has grown the most, to about 2.2 marks per paper.
• Only about 5% of questions are rated hard, so it is one of the most scorable subjects.
• The 2027 syllabus names the tabular method and circuit design explicitly.

Frequently Asked Questions

How many marks does Digital Logic carry in GATE CS?

The official pattern does not fix marks per CS subject. Across all 23 official GATE CS papers from 2014 to 2026, Digital Logic averaged 6.5 marks per paper, which is 6.5% of the 100-mark paper, with a range of 3 to 9.

Which Digital Logic topics are most important for GATE CS 2027?

Boolean algebra and minimisation (K-maps) carry the most marks. Number representation (two's complement, overflow and IEEE 754) is the fastest-growing topic, followed by sequential circuits.

Has the Digital Logic syllabus changed for GATE 2027?

The wording has changed. The 2027 syllabus names the algebraic, Karnaugh map and tabular minimisation methods, and says "design of" combinational and sequential circuits. The topics are the same as in 2026.

Which book is best for Digital Logic for GATE CS?

Digital Design by M. Morris Mano and Michael Ciletti covers the full syllabus.

Is IEEE 754 in Digital Logic or COA for GATE?

In the official syllabus, "number representation and arithmetic (fixed and floating point)" is listed under Digital Logic, so IEEE 754 belongs here.

Where can I practise GATE CS Digital Logic PYQs?

Every GATE CS question from 2014 to 2026 is free on Success Tracker's GATE CS PYQ archive, with the official answer and a worked solution.

Next in This Series

• Computer Organization and Architecture for GATE CS 2027
• Engineering Mathematics for GATE CS 2027
• Discrete Mathematics for GATE CS 2027
• GATE CSE subject-wise weightage
• GATE CS 2027 complete guide

Sources

• GATE 2027 CS Syllabus (PDF), IIT Madras: Section 2, Digital Logic
• GATE 2026 CS Syllabus (PDF), IIT Guwahati: Section 2 (for the comparison)
• GATE 2027 Question Paper Pattern, IIT Madras: marks distribution and negative marking
• Official GATE CS question papers and answer keys, 2014–2026 (23 papers), as reproduced on Success Tracker. Weightage figures are The ML Hub's own count, done on 25 October 2026.