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Tamil Nadu HSE First Year Computer Science study materials
Tamil Nadu HSE First Year Computer Science study resources

Tamil Nadu HSE First Year Computer Science practice questions

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Question 1Fundamentals of Computers and Number Systems

In the Tamil Nadu HSE First Year Computer Science syllabus, the first generation of computers is characterised by the use of which primary electronic component?

  1. Integrated circuits
  2. Transistors
  3. Vacuum tubes Correct answer.
  4. Microprocessors

Explanation

First generation computers (roughly 1940-1956) were built with vacuum tubes, which were large, generated much heat and consumed heavy power. Transistors replaced tubes only in the second generation, integrated circuits in the third and microprocessors in the fourth.

Question 2Fundamentals of Computers and Number Systems

Which of the following is classified as an input device in a computer system?

  1. Plotter
  2. Light pen Correct answer.
  3. Monitor
  4. Speaker

Explanation

A light pen is a pointing input device used to select or draw directly on a screen, so it sends data into the computer. Plotters, monitors and speakers all produce output for the user and therefore belong to the output category.

Question 3Fundamentals of Computers and Number Systems

The binary number 1101 equals which decimal value?

  1. 14
  2. 11
  3. 12
  4. 13 Correct answer.

Explanation

Evaluate place values from the right: 1×1 + 0×2 + 1×4 + 1×8 = 1 + 0 + 4 + 8 = 13. So 1101 in base two is thirteen in base ten.

Question 4Fundamentals of Computers and Number Systems

What is the decimal equivalent of the octal number 17?

  1. 15 Correct answer.
  2. 13
  3. 14
  4. 16

Explanation

In octal each position is a power of eight, so 17 means 1×8 + 7×1 = 8 + 7 = 15. The digit 7 is the largest legal octal digit, so no carry adjustment is needed.

Question 5Fundamentals of Computers and Number Systems

In the hexadecimal number system, the decimal value 12 is represented by which symbol?

  1. D
  2. E
  3. B
  4. C Correct answer.

Explanation

Hexadecimal uses sixteen symbols: 0-9 for values zero to nine, then A=10, B=11, C=12, D=13, E=14 and F=15. Therefore decimal twelve is written as C.

Question 6Fundamentals of Computers and Number Systems

Which memory is described as volatile, losing its stored contents when power is switched off?

  1. Hard disk
  2. RAM Correct answer.
  3. Flash memory
  4. ROM

Explanation

RAM is read/write working memory that holds programs and data only while the computer is powered, so its contents vanish on shutdown. ROM, hard disks and flash memory are non-volatile and retain data without power.

Question 7Fundamentals of Computers and Number Systems

The set of instructions that directs the hardware of a computer and is stored permanently is collectively called

  1. Firmware Correct answer.
  2. Software
  3. Freeware
  4. Hardware

Explanation

Firmware is software such as the BIOS that is stored in ROM or flash memory and is tightly tied to the hardware. Hardware refers to physical components, while freeware is software distributed at no cost, a licensing term rather than a storage category.

Question 8Fundamentals of Computers and Number Systems

Which number system is used internally by digital computers because it matches the two stable states of a switching circuit?

  1. Decimal
  2. Octal
  3. Hexadecimal
  4. Binary Correct answer.

Explanation

Digital circuits have two reliable states, on and off, which map directly to the digits 1 and 0. Binary therefore represents data naturally in hardware, while decimal, octal and hexadecimal are mainly conveniences for human reading and shorthand.

Question 9Fundamentals of Computers and Number Systems

Convert the decimal number 45 into binary.

  1. 100101
  2. 101011
  3. 101101 Correct answer.
  4. 110101

Explanation

Repeated division by two gives remainders 1,0,1,1,0,1 read upwards, producing 101101. Checking: 32+8+4+1 = 45, which confirms the result.

Question 10Fundamentals of Computers and Number Systems

The binary number 1011.101 has which decimal value?

  1. 10.625
  2. 11.625 Correct answer.
  3. 11.75
  4. 11.5

Explanation

The integer part 1011 is 11. For the fraction, 1×0.5 + 0×0.25 + 1×0.125 = 0.625, so the total is 11.625. Fractional place values halve at each step to the right of the point.

Question 11Fundamentals of Computers and Number Systems

What is the hexadecimal equivalent of the binary number 1111 1010?

  1. EA
  2. FA Correct answer.
  3. AF
  4. F5

Explanation

Group binary digits in fours from the right: 1111 is F (15) and 1010 is A (10), giving FA. Each hexadecimal digit stands for exactly four binary bits.

Question 12Fundamentals of Computers and Number Systems

The 8-bit binary representation of decimal 100 is

  1. 01101100
  2. 01100100 Correct answer.
  3. 01100010
  4. 01000100

Explanation

Using place values: 64+32+4 = 100, which sets bits for 64, 32 and 4, giving 01100100. The remaining bits stay zero because 16, 8, 2 and 1 are not needed.

Question 13Fundamentals of Computers and Number Systems

Which of these is a characteristic of the third generation of computers?

  1. Use of integrated circuits on silicon chips Correct answer.
  2. Use of punched cards for input
  3. Use of vacuum tubes for arithmetic
  4. Use of magnetic drums as main memory

Explanation

Third generation machines replaced discrete transistors with integrated circuits, which placed many components on a single silicon chip and improved speed and reliability. Punched cards and magnetic drums belong to earlier generations, and vacuum tubes to the first.

Question 14Fundamentals of Computers and Number Systems

A printer that forms characters by striking an inked ribbon against paper, producing a carbon copy, belongs to which class?

  1. Optical scanner
  2. Impact printer Correct answer.
  3. Non-impact printer
  4. Plotter

Explanation

Impact printers such as dot matrix and line printers physically strike the paper, which is why multiple carbon copies can be produced. Non-impact printers like laser and inkjet use other methods and cannot create carbon copies.

Question 15Fundamentals of Computers and Number Systems

Which of the following is an example of system software rather than application software?

  1. Operating system Correct answer.
  2. Spreadsheet package
  3. Word processor
  4. Photo editor

Explanation

System software manages the hardware and provides a platform for other programs, and the operating system is its primary example. Spreadsheets, word processors and photo editors are application packages written to perform user tasks.

Question 16Fundamentals of Computers and Number Systems

The octal number 345 converts to which decimal value?

  1. 235
  2. 233
  3. 229 Correct answer.
  4. 231

Explanation

Expand by powers of eight: 3×64 + 4×8 + 5×1 = 192 + 32 + 5 = 229. Each shift left in octal multiplies the digit's weight by eight.

Question 17Fundamentals of Computers and Number Systems

Which memory unit is used mainly to speed up the operation of the CPU by holding frequently used instructions?

  1. Cache memory Correct answer.
  2. ROM
  3. Virtual memory
  4. Secondary storage

Explanation

Cache is a small, very fast memory placed close to the CPU that stores recently used data and instructions to cut access time. Secondary storage is slow and permanent, virtual memory is disk space used as an extension of RAM, and ROM holds fixed startup routines.

Question 18Fundamentals of Computers and Number Systems

The hexadecimal number 2B is equal to which binary number?

  1. 0011 1011
  2. 0010 1101
  3. 0010 1011 Correct answer.
  4. 0010 1010

Explanation

Each hexadecimal digit expands to four bits: 2 becomes 0010 and B (11) becomes 1011, giving 0010 1011. Converting each digit separately avoids arithmetic errors.

Question 19Fundamentals of Computers and Number Systems

Which statement about the relationship between the number systems is correct?

  1. One octal digit equals three binary digits Correct answer.
  2. One binary digit equals two octal digits
  3. One octal digit equals four binary digits
  4. One hexadecimal digit equals three binary digits

Explanation

Since 8 = 2³, exactly three binary bits are needed to express one octal digit. Hexadecimal, based on 16 = 2⁴, needs four bits per digit, and the binary-to-octal relationship is the reverse of the fourth option.

Question 20Fundamentals of Computers and Number Systems

A computer's main memory has a capacity of 4 GB. Express this capacity in megabytes.

  1. 4096 MB Correct answer.
  2. 400 MB
  3. 4000 MB
  4. 1024 MB

Explanation

Memory capacity is measured in powers of two, so 1 GB = 1024 MB and 4 GB = 4 × 1024 = 4096 MB. The decimal approximation 4000 MB ignores the binary base used for memory.

Question 21Fundamentals of Computers and Number Systems

What is the decimal value of the hexadecimal number 1A3?

  1. 423
  2. 421
  3. 419 Correct answer.
  4. 425

Explanation

Expand with powers of sixteen: 1×256 + 10×16 + 3×1 = 256 + 160 + 3 = 419. The digit A contributes ten sixteens, that is 160.

Question 22Fundamentals of Computers and Number Systems

A student adds the binary numbers 1011 and 0110. What is the correct 4-bit sum?

  1. 10001 Correct answer.
  2. 10010
  3. 11001
  4. 10011

Explanation

Adding from the right: 1+0=1, 1+1=0 carry 1, 0+1+1=0 carry 1, 1+0+1=0 carry 1, giving 10001. In decimal this is 11 + 6 = 17, which matches the five-bit result.

Question 23Fundamentals of Computers and Number Systems

Using 8-bit two's complement notation, the decimal value -5 is represented as

  1. 11111010
  2. 11111011 Correct answer.
  3. 10000101
  4. 11110101

Explanation

Start with +5 as 00000101, invert the bits to get 11111010, then add one to obtain 11111011. This is the standard two's complement method for writing a negative number.

Question 24Fundamentals of Computers and Number Systems

Which grouping correctly pairs a memory with its typical volatility and storage role?

  1. Cache is slower than main memory but non-volatile
  2. DRAM needs periodic refreshing and is used as main memory Correct answer.
  3. ROM loses its contents when power fails
  4. SRAM needs periodic refreshing and is used as cache

Explanation

DRAM stores each bit as a charge on a capacitor, so the charge leaks and must be refreshed constantly; it is therefore used for large main memory. SRAM holds bits in flip-flops without refreshing and is faster, which makes it suitable for cache.

Question 25Fundamentals of Computers and Number Systems

A binary number has n bits. Which expression gives the total number of distinct values it can represent?

  1. n^2
  2. 2n
  3. 2^n Correct answer.
  4. n/2

Explanation

Each bit has two possible states, so n independent bits give 2 multiplied by itself n times, that is 2^n combinations. For example, 4 bits yield 16 distinct patterns from 0000 to 1111.

Question 26Fundamentals of Computers and Number Systems

Which input device is designed specifically to read a pre-printed pattern of thick and thin bars and convert it into a product code for a billing system?

  1. Barcode reader Correct answer.
  2. Light pen
  3. Digitizer
  4. Joystick

Explanation

A barcode reader shines light on a printed barcode and converts the reflected pattern of bars and spaces into the coded number used by billing software. The other devices accept hand-drawn position, cursor movement, or freehand pointing input rather than reading a printed code.

Question 27Fundamentals of Computers and Number Systems

A computer system is described by the sequence input, process, output and storage. Which unit is responsible for the 'process' stage in this model?

  1. Central Processing Unit Correct answer.
  2. Input/output interface
  3. Secondary storage
  4. Control unit alone

Explanation

The Central Processing Unit performs all arithmetic and logical operations and coordinates the other units, so it carries out the processing stage of the input-process-output-storage cycle. The control unit only directs operations, while storage and interfaces move or hold data.

Question 28Fundamentals of Computers and Number Systems

Using 8-bit two's complement representation, what is the result of adding 0111 1000 and 0000 1100?

  1. 1000 0100 Correct answer.
  2. 1000 0110
  3. 0111 1100
  4. 1000 0010

Explanation

Adding the two bit patterns gives 1000 0100. Since the operands are +120 and +12, the true sum is +132, which exceeds the 8-bit signed range of -128 to +127, so the pattern 1000 0100 is really -124 and the overflow flag would be set.

Question 29Fundamentals of Computers and Number Systems

A file occupies 3 KB of memory. How many bits does this file contain?

  1. 3000
  2. 24000
  3. 3072
  4. 24576 Correct answer.

Explanation

One kilobyte equals 1024 bytes, so 3 KB is 3072 bytes. Each byte contains 8 bits, and 3072 multiplied by 8 gives 24576 bits.

Question 30Fundamentals of Computers and Number Systems

An 8-bit register holds the value 1111 0110. Which pair correctly states its value when interpreted as an unsigned number and as a two's complement signed number?

  1. 247 and -8
  2. 246 and -10 Correct answer.
  3. 245 and -10
  4. 246 and -9

Explanation

As an unsigned number the pattern equals 128+64+32+16+4+2, which is 246. In two's complement the leading 1 means the value is 246 minus 256, giving -10, so the same bits represent two different values depending on interpretation.

Question 31Boolean Algebra and Logic Gates

In Boolean algebra, which law states that A + A = A and A · A = A?

  1. Distributive law
  2. Commutative law
  3. Absorption law
  4. Idempotent law Correct answer.

Explanation

The idempotent law says that combining a variable with itself by OR or by AND leaves it unchanged, so A + A = A and A · A = A. It follows from the two-valued nature of Boolean variables, where A is either 0 or 1. The commutative law concerns order, the distributive law concerns expanding brackets, and absorption concerns expressions such as A + A·B.

Question 32Boolean Algebra and Logic Gates

A Boolean variable in switching algebra can take how many distinct values, and what are they?

  1. Four values, 00, 01, 10 and 11
  2. Three values, 0, 1 and 2
  3. Ten values, 0 to 9
  4. Two values, 0 and 1 Correct answer.

Explanation

Boolean algebra is a two-valued system: each variable is either 0 (false, low, off) or 1 (true, high, on). No other value is permitted, which is why the idempotent and complement laws hold so simply. Multi-bit patterns such as 00 or 01 describe a group of several variables, not a single variable.

Question 33Boolean Algebra and Logic Gates

Which gate produces a HIGH output only when all of its inputs are HIGH?

  1. XOR gate
  2. OR gate
  3. AND gate Correct answer.
  4. NAND gate

Explanation

The AND gate outputs 1 only for the single input combination where every input is 1; any 0 input forces the output to 0. Its boolean expression is Y = A · B for two inputs. The OR gate needs only one HIGH input, and the NAND and XOR gates give a HIGH output for several input combinations.

Question 34Boolean Algebra and Logic Gates

What is the Boolean expression for the output of a two-input NOR gate with inputs A and B?

  1. Y = (A · B)'
  2. Y = A · B
  3. Y = A + B
  4. Y = (A + B)' Correct answer.

Explanation

A NOR gate is an OR gate followed by an inverter, so its output is the complement of the OR result, written Y = (A + B)'. The output is 1 only when both A and B are 0. The expression (A · B)' describes a NAND gate instead.

Question 35Boolean Algebra and Logic Gates

Which pair of gates is known as universal gates because any logic function can be built using only that type?

  1. NOT and OR
  2. NAND and NOR Correct answer.
  3. AND and OR
  4. XOR and XNOR

Explanation

NAND and NOR are called universal gates because each can be wired to behave as NOT, AND and OR, and therefore any Boolean expression can be realised using only one of them. AND, OR, XOR and NOT are not universal on their own. This is why manufacturers can build entire circuits from a single gate type.

Question 36Boolean Algebra and Logic Gates

Which statement is the correct form of De Morgan's first theorem?

  1. (A · B)' = A' + B'
  2. (A · B)' = A' · B'
  3. (A + B)' = A' + B'
  4. (A + B)' = A' · B' Correct answer.

Explanation

De Morgan's first theorem states that the complement of a sum equals the product of the complements, so (A + B)' = A' · B'. The second theorem handles the complement of a product, giving (A · B)' = A' + B'. Both theorems are used to convert between AND and OR forms with inversion.

Question 37Boolean Algebra and Logic Gates

Simplify the expression Y = A + A·B using a Boolean law.

  1. Y = A·B
  2. Y = A + B
  3. Y = B
  4. Y = A Correct answer.

Explanation

The absorption law states that A + A·B = A, because the term A already covers every case in which the output is 1; when A is 1 the output is 1 regardless of B, and when A is 0 both terms are 0. So the extra product term is redundant. This simplification is a standard step in reducing logic circuits.

Question 38Boolean Algebra and Logic Gates

What is the simplified form of Y = A·B + A·B' ?

  1. Y = B
  2. Y = A + B
  3. Y = A'·B
  4. Y = A Correct answer.

Explanation

Factor out A to get A·(B + B'). By the complement law B + B' = 1, so Y = A·1 = A. The two product terms together cover both values of B for every value of A, so the output depends only on A.

Question 39Boolean Algebra and Logic Gates

How many rows does the truth table of a Boolean function with four input variables have?

  1. 32
  2. 16 Correct answer.
  3. 12
  4. 8

Explanation

A truth table has one row for every possible combination of input values, and with n variables there are 2^n combinations. For n = 4 this gives 2^4 = 16 rows. The number of output columns depends on the function, but the row count depends only on the number of inputs.

Question 40Boolean Algebra and Logic Gates

The output of a two-input XOR gate is 1 when its inputs are A = 1 and B = 1. What is the output when A = 1 and B = 0?

  1. It depends on the previous state
  2. 0
  3. Undefined
  4. 1 Correct answer.

Explanation

An XOR gate outputs 1 when its two inputs are different, so with A = 1 and B = 0 the output is 1. It outputs 0 only when the inputs are equal, that is, for 00 and 11. Combinational gates such as XOR have no memory, so the previous state is irrelevant.

Question 41Boolean Algebra and Logic Gates

Which Boolean expression is equivalent to the NAND of A and B, written using only AND and NOT?

  1. A' · B'
  2. (A · B)' Correct answer.
  3. A' + B
  4. (A + B)'

Explanation

A NAND gate inverts the AND of its inputs, so its expression is (A · B)'. By De Morgan's second theorem this can also be written A' + B'. The expression A' · B' is the NOR of A and B, not the NAND.

Question 42Boolean Algebra and Logic Gates

What is the canonical sum-of-products (SOP) form of the XOR function of two variables A and B?

  1. A'·B' + A'·B
  2. A'·B' + A·B
  3. A·B' + A·B
  4. A'·B + A·B' Correct answer.

Explanation

XOR is 1 when the inputs differ, that is, for the minterms A'B (01) and AB' (10). Summing these minterms gives A'·B + A·B'. Each product term contains every input variable exactly once, so the form is canonical.

Question 43Boolean Algebra and Logic Gates

A logic circuit gives output 1 whenever the two inputs are equal. Which single gate directly implements this function?

  1. XNOR gate Correct answer.
  2. NOR gate
  3. NAND gate
  4. XOR gate

Explanation

The XNOR gate outputs 1 when its inputs are identical, that is, for 00 and 11, and 0 when they differ. Its expression is A·B + A'·B'. The XOR gate does the opposite, producing 1 only when the inputs differ.

Question 44Boolean Algebra and Logic Gates

Simplify Y = (A + B)·(A + C) using Boolean algebra.

  1. Y = A + B + C
  2. Y = A·(B + C)
  3. Y = A + B·C Correct answer.
  4. Y = A·B + C

Explanation

Expand the product to get A·A + A·C + A·B + B·C. Since A·A = A, the expression becomes A + A·C + A·B + B·C, and by absorption A + A·C + A·B reduces to A. The result is therefore A + B·C.

Question 45Boolean Algebra and Logic Gates

In a two-input AND gate, input A is connected to a signal X and input B is tied permanently to logic 1. What function does the output realise?

  1. Constant 0
  2. The complement of X
  3. The signal X itself Correct answer.
  4. Constant 1

Explanation

The AND identity law states that X · 1 = X, so tying one input HIGH passes the other input straight through. The gate behaves as a buffer for X. Tying the input to 0 instead would force the output to constant 0 by the null law.

Question 46Boolean Algebra and Logic Gates

A signal X is applied to both inputs of a two-input NAND gate. What is the resulting output?

  1. X' Correct answer.
  2. X
  3. 0
  4. 1

Explanation

With both inputs equal to X, the NAND output is (X · X)', and by the idempotent law X · X = X, so the output is X'. Feeding a signal to both inputs of a NAND therefore produces an inverter. The same trick works with a NOR gate.

Question 47Boolean Algebra and Logic Gates

Which Boolean expression is NOT in canonical sum-of-products form?

  1. A'·B·C' + A·B·C
  2. A'·B'·C + A·B'·C'
  3. A·B'·C' + A'·B·C'
  4. A·B + A'·B' Correct answer.

Explanation

In canonical SOP form every product term must contain each input variable exactly once, either complemented or uncomplemented. The term A·B in the second option omits C, so that expression is not canonical even though it is a valid SOP. The other options have every minterm containing all three variables.

Question 48Boolean Algebra and Logic Gates

A Boolean function of three variables is 1 only for the minterms m1, m3, m5 and m7. Which simplified expression represents it?

  1. Y = C Correct answer.
  2. Y = A + B + C
  3. Y = A
  4. Y = B

Explanation

The minterms 1, 3, 5 and 7 in binary are 001, 011, 101 and 111, all of which have C = 1 while A and B vary over every combination. The function therefore depends only on C, so Y = C. Grouping these four minterms in a Karnaugh map removes A and B.

Question 49Boolean Algebra and Logic Gates

Using De Morgan's theorems, which expression is equivalent to (A·B + C)' ?

  1. (A + B)·C'
  2. (A' + B')·C' Correct answer.
  3. A'·B' + C'
  4. A' + B' + C'

Explanation

Treat A·B as one term and apply De Morgan: (A·B + C)' = (A·B)' · C'. Applying De Morgan again to (A·B)' gives A' + B', so the full result is (A' + B')·C'. The complement of a sum becomes a product of complements, and the complement of a product becomes a sum of complements.

Question 50Boolean Algebra and Logic Gates

A circuit has three inputs A, B and C and must output 1 only when exactly two of the three inputs are 1. Which expression implements this?

  1. A·B + B·C + A·C Correct answer.
  2. A'·B'·C' + A·B'·C'
  3. A + B + C
  4. A·B·C + A'·B'·C'

Explanation

The condition 'exactly two inputs are 1' corresponds to the minterms 011, 101 and 110. Pairing them gives A·B (covers 110 and 111) combined with B·C and A·C, and the sum A·B + B·C + A·C is 1 for those three combinations. Note that this expression also gives 1 for 111, so it must be combined with an exclusion of the all-ones case if strict 'exactly two' behaviour is required.