Question 1

Bit grouping and storage size: consider the binary string “1011 1001 0110 1110”. How many bytes of data does this 16-bit pattern occupy?

Accepted Answer

Introduction / Context: Understanding how bits aggregate into bytes and words is vital for memory sizing, data alignment, and communication protocols. The given pattern contains 16 bits grouped as four nibbles (4-bit groups), commonly written with a space every 4 bits for readability. Given Data / Assumptions: Total bit count: 16 bits (1011 1001 0110 1110). 1 byte = 8 bits, 1 nibble = 4 bits. No parity or additional overhead bits are included; it is a raw bit count question. Concept / Approach: Compute the number of bytes using the simple identity: bytes = total_bits / 8. This is a direct unit conversion from bits to bytes with no rounding since 16 is an exact multiple of 8. Step-by-Step Solution: Count bits: 4 groups * 4 bits per group = 16 bits. Convert units: bytes = 16 / 8 = 2. Therefore the 16-bit pattern occupies 2 bytes of storage. Verification / Alternative check: Break into two bytes explicitly: first byte 10111001 (B9 in hex), second byte 01101110 (6E in hex). Two bytes are present, confirming the calculation. Why Other Options Are Wrong: 1: Would correspond to 8 bits, not 16 bits. 4 or 8: Would require 32 or 64 bits respectively. None: incorrect because 2 bytes is exact. Common Pitfalls: Confusing nibbles and bytes, or miscounting due to visual spacing. Spaces in binary strings are for readability only and do not change the bit count. Final Answer: 2

Question 2

Boolean algebra identities: which option correctly states the commutative law in Boolean algebra (choose the statement that explicitly shows operands can swap order without changing the result)?

Accepted Answer

Introduction / Context: Boolean algebra underpins digital logic design. Several fundamental identities are frequently tested: commutative, associative, distributive, and idempotent laws. This question focuses on identifying the commutative law, which states that operands may be exchanged without affecting the result. Given Data / Assumptions: Symbol “+” denotes logical OR; symbol “*” (or adjacency) denotes logical AND. We compare several identities to determine which one explicitly demonstrates operand interchangeability. Standard Boolean algebra rules apply. Concept / Approach: The commutative laws are: A + B = B + A and A * B = B * A. They specifically show that the order of operands does not matter for OR or AND. Other identities (associative, distributive, idempotent) express different properties and should not be confused with commutativity. Step-by-Step Solution: Review each option and classify its identity type. Identify the statement that swaps operand order without changing the result. Select A + B = B + A as the commutative law for OR. Verification / Alternative check: Test with values: let A=0, B=1. A + B = 1 and B + A = 1, therefore the equality holds and demonstrates operand order irrelevance. Why Other Options Are Wrong: A * (B + C) = A*B + A*C: distributive law, not commutative. (A + B) + C = A + (B + C): associative law for OR. A + A = A: idempotent law for OR. None: incorrect because a correct commutative statement is present. Common Pitfalls: Confusing distributive with commutative due to similar symbol patterns, and overlooking that commutativity solely concerns swapping operands, not grouping or distribution. Final Answer: A + B = B + A

Question 3

Gate behavior check: a multi-input NOR gate produces a logic HIGH at its output only for which specific input pattern?

Accepted Answer

Introduction / Context: NOR is a fundamental logic gate defined as the logical complement of OR. Understanding its truth condition is crucial for designing active-low control signals, reset lines, and simple condition detectors. The question asks which input pattern yields a HIGH (1) at the output of a NOR gate. Given Data / Assumptions: NOR output = NOT(OR of all inputs). Inputs are standard binary values (0 or 1). We consider a NOR with two or more inputs; the property generalizes. Concept / Approach: By definition, OR outputs 1 if any input is 1. Therefore, NOR outputs 1 only when OR would output 0, which happens exclusively when every input is 0. Thus, NOR is an “all-zero detect” gate in its simplest interpretation. Step-by-Step Solution: Write relation: Y = NOR(A, B, …) = NOT(A + B + …). OR is 0 only when A = B = … = 0. Therefore Y = 1 exactly when all inputs are 0. Verification / Alternative check: Truth table inspection for 2-input NOR shows Y=1 only for A=0, B=0. Extending to more inputs preserves the condition: any single 1 forces OR to 1, making NOR 0. Why Other Options Are Wrong: Mix of 0s and 1s: OR becomes 1, so NOR becomes 0. All 1s: OR is 1, so NOR is 0. “Any inputs…”: ignores the defining complement relation to OR. None: incorrect because the all-zero condition is correct and present. Common Pitfalls: Confusing NOR with NAND; NAND outputs 0 only when all inputs are 1, whereas NOR outputs 1 only when all inputs are 0. Final Answer: All inputs are 0s

Question 4

Computer taxonomy: a microcomputer is defined as a computer that uses which component as its central processing unit (CPU)?

Accepted Answer

Introduction / Context: Computer classes historically include microcomputers, minicomputers, and mainframes. The hallmark of a microcomputer is that its CPU is implemented on a single integrated circuit: the microprocessor. This integration drastically reduced cost and physical size, fueling personal computing. Given Data / Assumptions: CPU is the central processing element executing instructions. A microprocessor integrates ALU, registers, and control logic on one chip. We distinguish microcomputers from earlier designs built from many discrete components. Concept / Approach: When the CPU is realized as a microprocessor, the entire computer can be built around it with memory, I/O, and support chips. This design contrasts with CPUs built from multiple boards or vacuum tubes. The single-chip CPU is the defining criterion for a microcomputer. Step-by-Step Solution: Identify the defining feature: CPU on a single IC. Map that feature to the correct term: microprocessor. Select the answer indicating a microprocessor-based CPU. Verification / Alternative check: Classic examples: systems based on Intel 8080/8086, Motorola 68000, or modern x86/ARM SoCs are microprocessor-based and therefore microcomputers (at the personal scale or embedded scale). Why Other Options Are Wrong: Multiple discrete chips or registers: describes older or custom CPUs, not a microcomputer definition. Vacuum tube CPU: characteristic of early mainframes, not microcomputers. None: incorrect because microprocessor is the standard definition. Common Pitfalls: Confusing “microcontroller” with “microprocessor”: a microcontroller includes CPU + memory + peripherals on one chip; many microcomputers can still be built around a microcontroller. Final Answer: A microprocessor

Question 5

Boolean evaluation: which of the following Boolean OR expressions is incorrect under standard Boolean algebra rules (where 1 represents logic HIGH and “+” denotes OR)?

Accepted Answer

Introduction / Context: Boolean algebra uses 1 and 0 to denote TRUE and FALSE (or HIGH and LOW). The OR operation (“+”) outputs 1 if any operand is 1. This question asks you to identify which expression violates the standard truth of OR. Given Data / Assumptions: Use standard Boolean OR: 0 + 0 = 0; 0 + 1 = 1; 1 + 0 = 1; 1 + 1 = 1. Associativity allows grouping without changing results. We assume no XOR; “+” is strictly OR here. Concept / Approach: Check each option against the OR truth rules. Any sum including a 1 must be 1, including 1 + 1 which equals 1, not 0. Multi-operand OR remains 1 if at least one operand is 1. Step-by-Step Solution: Evaluate 1 + 0: equals 1 → correct. Evaluate 1 + 1: equals 1 → the option stating 0 is incorrect. Evaluate 1 + 0 + 1: at least one 1 → equals 1 → correct. Evaluate 1 + 1 + 1: equals 1 → correct. Verification / Alternative check: Truth tables confirm 1 OR 1 = 1. No standard Boolean system makes 1 + 1 = 0; that result would correspond to XOR, not OR. Why Other Options Are Wrong: 1 + 0 = 1: valid OR identity. 1 + 0 + 1 = 1 and 1 + 1 + 1 = 1: valid due to presence of 1s. None: invalid because there is indeed one incorrect expression (1 + 1 = 0). Common Pitfalls: Confusing OR with XOR; XOR of 1 and 1 is 0, but this question uses OR (+), not XOR (⊕). Final Answer: 1 + 1 = 0

Question 6

Binary subtraction practice: compute (1110101010)_2 − (100101100)_2 and select the correct binary result.

Accepted Answer

Introduction / Context: Binary arithmetic underlies computer operations at the hardware level. This exercise tests accurate subtraction of two unsigned binary numbers and recognition of the correct result among plausible distractors. Given Data / Assumptions: Minuend = 1110101010 (base 2). Subtrahend = 100101100 (base 2). Treat both as unsigned binary integers; no sign bits involved. Concept / Approach: We can subtract using either direct binary column subtraction with borrows or convert to decimal for a cross-check. Converting to decimal often provides a quick sanity check before re-encoding the result back to binary. Step-by-Step Solution: Convert minuend: 1110101010₂ = 1*512 + 1*256 + 1*128 + 0*64 + 1*32 + 0*16 + 1*8 + 0*4 + 1*2 + 0*1 = 938. Convert subtrahend: 100101100₂ = 1*256 + 0*128 + 0*64 + 1*32 + 0*16 + 1*8 + 1*4 + 0*2 + 0*1 = 300. Subtract in decimal: 938 − 300 = 638. Convert 638 back to binary: 638 = 512 + 126 = 512 + 64 + 32 + 16 + 8 + 4 + 2 = binary 10 0111 1110 → 1001111110₂. Verification / Alternative check: Perform column-wise binary subtraction with borrows; the final bits match 1001111110, confirming the decimal cross-check result. Why Other Options Are Wrong: 1001011110: close-looking distractor but equals 638 − 32 = 606, not our difference. 0110100001 and 1111000001: mismatched magnitudes; converting to decimal shows incorrect values. None: invalid because a correct option is present. Common Pitfalls: Misaligning bit positions due to different operand lengths; always align the least significant bits. Also, forgetting borrows in binary column subtraction yields off-by-powers-of-two errors. Final Answer: 1001111110

Question 7

Digital design classification: are parallel adders considered combinational or sequential circuits, and why?

Accepted Answer

Introduction / Context: Parallel adders are fundamental arithmetic building blocks in ALUs and datapaths. Correctly classifying them as combinational or sequential helps in timing analysis, verification, and synthesis strategies. Given Data / Assumptions: A parallel adder takes two multi-bit operands (and possibly a carry-in) and produces a sum vector and a carry-out. No internal storage is required to hold state across clock cycles for the basic operation. We consider the canonical ripple-carry or carry-lookahead implementations. Concept / Approach: Combinational circuits produce outputs that are pure functions of current inputs, without memory of past inputs. Sequential circuits incorporate storage (flip-flops or latches) and depend on both present inputs and past state. Parallel adders compute sums immediately from their inputs using logic gates (half-adders/full-adders), so they are combinational by definition. Step-by-Step Solution: Model a 1-bit full adder: outputs Sum and Cout depend on A, B, Cin only. Cascade N full adders for N-bit operands to form a parallel adder. Observe no flip-flops are required; result depends solely on current A, B, Cin. Verification / Alternative check: Timing analysis treats delays as combinational path delays (e.g., ripple-carry path). If registers are added around the adder, that forms a pipelined system, but the adder block itself remains combinational. Why Other Options Are Wrong: Sequential: would require state elements; a pure adder has none. Both/All of the above: incorrect because the primitive adder block is purely combinational. None: invalid because a correct classification exists. Common Pitfalls: Confusing system-level designs (e.g., registered adders in pipelines) with the intrinsic nature of the adder logic block. Registers around an adder do not change the adder’s combinational nature. Final Answer: Combinational logic circuits

Question 8

RS flip-flop behavior (set–reset latch): Assume an RS flip-flop with both inputs initially at 0 (R = 0 and S = 0, stable hold condition) and the output Q starting at 0. If a momentary 1 (a brief high pulse) is applied to the S input while R remains …

Accepted Answer

Introduction / Context: This question tests understanding of the fundamental behavior of an RS (Set–Reset) flip-flop, also called an SR latch. Knowing how Q responds to brief set or reset pulses is crucial for designing debouncers, edge detectors, and simple memory elements in digital electronics. Given Data / Assumptions: Initial condition: R = 0, S = 0 (the hold state), and Q = 0. A momentary 1 (short pulse) is applied to S while R remains 0. After the pulse, S returns to 0 (so S = 0 and R = 0 again). We consider a typical active-high RS latch with cross-coupled gates (NOR or NAND as appropriate for active levels). Concept / Approach: In an active-high RS latch, asserting S = 1 drives the latch into the set state. Once set, the internal cross-coupling provides positive feedback that maintains Q = 1 even after S returns to 0, as long as R stays at 0. This is the essence of memory in a latch: it holds the last commanded state until another valid command (reset) arrives. Step-by-Step Solution: Start: R = 0, S = 0, Q = 0 → stable hold at Q = 0.Apply a brief set pulse: S = 1, R = 0 → the latch sets, forcing Q = 1.Remove the pulse: S returns to 0 while R = 0 → the latch is back in the hold state but now holds Q = 1.Conclusion: Q flips from 0 to 1 and remains 1 until a reset (R = 1) occurs. Verification / Alternative check: Truth behavior of a NOR-latch (active-high): S = 1, R = 0 → Q = 1 (set). Returning both to 0 keeps the last state. Only R = 1 will reset Q to 0. This aligns with standard timing diagrams of SR latches. Why Other Options Are Wrong: (a) A latch does not free-run; it is level-sensitive storage. (b) Returning S to 0 does not undo the set; only R = 1 resets. (c) R = 0 does not force Q low; it merely refrains from resetting. (e) Metastability is associated with illegal inputs (S = R = 1) or setup/hold violations, not a clean S pulse. Common Pitfalls: Confusing hold (S = 0, R = 0) with reset; thinking that S must stay 1 to keep Q = 1; or mixing NOR-latch (active-high) with NAND-latch polarity. Always check active levels and the last commanded state. Final Answer: Q flips from 0 to 1 and remains latched at 1 after S returns to 0.

Question 9

Binary fixed-point arithmetic: Find the 2's complement of the binary fraction 0.01011 (assume a fixed 5-bit fractional field; express the result with the same binary point position).

Accepted Answer

Introduction / Context: The 2's complement operation is the standard way to represent signed numbers in binary for both integers and fixed-point fractions. For a fixed fractional width, you can compute the negative of a value by taking the 1's complement (bitwise invert within the field) and then adding 1 at the least significant fractional bit. This problem reinforces that the same rule applies to binary fractions as to integers, provided the bit width is fixed. Given Data / Assumptions: Original value: 0.01011 (5 fractional bits). We seek its 2's complement within the same 1.fraction format (carry may appear to the left of the point). No change in fractional precision (still 5 bits after the binary point). Concept / Approach: For a fixed n-bit fractional field f[1..n], the 2's complement is obtained by: invert all n bits → add 1 at the least significant position. This yields the representation of the negative value within the same fixed-point word length. Because addition can generate a carry into the integer position, results often appear as 1.xxxxx for negative values. Step-by-Step Solution: Start with 0.01011 (fractional field = 01011).Compute 1's complement: invert bits → 10100.Add 1 at LSB: 10100 + 00001 = 10101.Place the binary point consistently: result = 1.10101 in the same fixed-point word. Verification / Alternative check: Numeric check using decimal equivalents: 0.01011₂ = 11/32 = 0.34375. The 2's complement within 1.fffff format represents −0.34375. Evaluate 1.10101 as 1 − 0.01011 = 0.65625; interpreted in 2's complement fixed-point, that code corresponds to −0.34375, confirming correctness. Why Other Options Are Wrong: (b) and (d) use 0.x forms that are just complements without sign, not 2's complement negatives. (c) has an incorrect +1 step (produced 10100 rather than 10101). (e) is invalid because a correct choice exists. Common Pitfalls: Forgetting the add-1 step after inversion; changing the binary point position; or assuming variable precision instead of fixed 5-bit fraction. Final Answer: 1.10101.

Question 10

Hex to binary conversion: Convert the hexadecimal number 93FA₁₆ to its binary equivalent (group in 4-bit nibbles for clarity).

Accepted Answer

Introduction / Context: Hexadecimal is a compact human-readable notation for binary because each hex digit corresponds to exactly four binary bits (a nibble). Converting hex to binary is therefore a straightforward substitution task—ideal practice for digital design and low-level programming. Given Data / Assumptions: Hex input: 93FA₁₆. We must write the exact binary sequence. Mapping is 0→0000 through F→1111. Concept / Approach: Replace each hex digit with its 4-bit binary equivalent: 9→1001, 3→0011, F→1111, A→1010. Concatenate in the same order to form the full binary number. Step-by-Step Solution: Write nibbles: 9 3 F A.Convert: 9→1001, 3→0011, F→1111, A→1010.Concatenate: 1001 0011 1111 1010 → 1001001111111010₂. Verification / Alternative check: Back-convert by grouping the binary into nibbles: 1001 0011 1111 1010 → 9 3 F A → 93FA₁₆. The round-trip confirms accuracy. Why Other Options Are Wrong: (b) has an extra bit. (c) and (d) contain scrambled groupings that do not reproduce 93FA₁₆. (e) is invalid since a correct option exists. Common Pitfalls: Dropping leading zeros within a nibble or mis-grouping bits. Keep 4 bits per hex digit. Final Answer: 1001001111111010₂.

Question 11

Octal to binary conversion: Convert the octal number 134₈ to its binary representation, preserving leading zeros per octal-to-binary mapping.

Accepted Answer

Introduction / Context: Octal (base-8) digits map neatly to binary in groups of three bits because 8 = 2^3. Converting octal to binary is therefore a simple table-lookup process per digit. Given Data / Assumptions: Octal number: 134₈. Digit mappings: 1→001, 3→011, 4→100. We keep each 3-bit group to avoid ambiguity. Concept / Approach: Translate each octal digit to its 3-bit binary equivalent and concatenate in order. Leading zeros within a group are retained to preserve the 3-bit alignment that reflects the original octal digits. Step-by-Step Solution: Map: 1→001, 3→011, 4→100.Concatenate: 001 011 100 → 001011100₂. Verification / Alternative check: Convert back by grouping binary in 3s: 001→1, 011→3, 100→4 → 134₈. The cycle validates the result. Why Other Options Are Wrong: (a) differs in the middle group, (b) mismaps groups, (d) discards necessary leading zeros and groups incorrectly. Common Pitfalls: Omitting leading zeros in the leftmost group and misreading the resulting octal digits. Final Answer: 001011100₂.

Digital Computer Electronics Questions