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WBCHSE HS Modern Computer Application study materials
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WBCHSE HS Modern Computer Application practice questions

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Question 1Introduction to Computer System and Computer Organization

Which component of the CPU fetches instructions, decodes them and coordinates the working of all other units?

  1. Program Counter
  2. Control Unit Correct answer.
  3. Accumulator
  4. Arithmetic Logic Unit

Explanation

The control unit fetches each instruction from memory, decodes it to find out which operation is required, and then issues control signals that make the other units carry out that operation. The ALU only performs the arithmetic and logical operations themselves, while registers such as the program counter and accumulator only hold addresses or data.

Question 2Introduction to Computer System and Computer Organization

Which type of memory loses all its stored contents as soon as the power supply is switched off?

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

Explanation

RAM is volatile: every cell needs a continuous power supply to hold its stored bit, so the entire contents disappear when the machine is switched off. ROM, flash memory and hard disks are non-volatile and keep their stored data even without power.

Question 3Introduction to Computer System and Computer Organization

A printed photograph has to be converted into a digital file that can be edited on a computer. Which device is used for this purpose?

  1. Speaker
  2. Scanner Correct answer.
  3. Plotter
  4. Printer

Explanation

A scanner throws light on the sheet and senses the reflected light to build a digital image, so a printed photograph becomes a file that editing software can open. Plotters and printers only produce output on paper, and a speaker produces sound output.

Question 4Introduction to Computer System and Computer Organization

During a memory read operation, which bus carries the binary address of the memory location that the CPU wants to access?

  1. Expansion bus
  2. Control bus
  3. Data bus
  4. Address bus Correct answer.

Explanation

The address bus is unidirectional and carries the address of the memory location or I/O port selected by the CPU. The data bus then carries the actual contents to or from that location, while the control bus carries timing and read/write signals.

Question 5Introduction to Computer System and Computer Organization

Which sequence correctly shows the three steps of the instruction cycle of a CPU?

  1. Fetch → Decode → Execute Correct answer.
  2. Fetch → Execute → Decode
  3. Decode → Fetch → Execute
  4. Execute → Fetch → Decode

Explanation

In every machine cycle the CPU first fetches the instruction from the location given by the program counter, then decodes the opcode held in the instruction register to identify the operation, and only after that executes it. The program counter is then updated so that the next fetch starts at the following instruction.

Question 6Introduction to Computer System and Computer Organization

Why is a small cache memory placed between the CPU and the main memory?

  1. It keeps often-used data and instructions near the CPU. Correct answer.
  2. It converts analog signals from sensors into digital data.
  3. It permanently stores the operating system for booting.
  4. It adds extra RAM chips to the main board.

Explanation

Cache is a small, very fast memory that holds copies of the instructions and data the CPU is using most frequently. Because it is closer to the processor and faster than RAM, the average time needed to fetch a word is reduced, which raises the overall execution speed.

Question 7Introduction to Computer System and Computer Organization

Which feature distinguishes secondary storage from main memory?

  1. It is accessed directly by the ALU during execution.
  2. It keeps its contents when the power is switched off. Correct answer.
  3. It is faster to access than CPU registers are.
  4. It stores only the currently running program.

Explanation

Secondary storage such as hard disks, SSDs and pen drives is non-volatile, so programs and files remain stored after the computer is switched off. Main memory is volatile and much faster, and only the currently running program and its data need to be held there.

Question 8Introduction to Computer System and Computer Organization

Which of the following is normally stored permanently in a ROM chip on the motherboard?

  1. The program that is currently executing
  2. The data copied to the clipboard last
  3. The documents last saved by the user
  4. The BIOS firmware needed during startup Correct answer.

Explanation

The ROM chip holds firmware such as the BIOS or UEFI, which is needed to test the hardware and begin loading the operating system when the machine is switched on. User documents, running programs and clipboard contents are kept in RAM or on secondary storage and are not permanent.

Question 9Introduction to Computer System and Computer Organization

Which statement about Direct Memory Access (DMA) is correct?

  1. It raises the clock speed of the processor when many input devices are active.
  2. It permanently copies the BIOS program into the cache during system boot.
  3. It moves data between an I/O device and memory without per-byte CPU work. Correct answer.
  4. It saves the program counter value to memory whenever an interrupt is received.

Explanation

With DMA, a dedicated DMA controller takes charge of the transfer and moves a block of bytes between the device and main memory directly while the CPU continues with other work. The CPU is interrupted only once, when the whole block has been transferred, so the overhead of handling each byte is avoided.

Question 10Introduction to Computer System and Computer Organization

A computer has a 20-bit address bus, and each memory location stores one byte. What is the maximum amount of main memory that the CPU can address directly?

  1. 640 KB
  2. 1 MB Correct answer.
  3. 2 MB
  4. 20 KB

Explanation

Each of the 2^20 different addresses selects one byte, and 2^20 bytes equals 1,048,576 bytes, which is 1 MB. Adding one more address line would double the addressable space to 2 MB, so 20 bits give only 1 MB.

Question 11Introduction to Computer System and Computer Organization

In the stored-program concept of von Neumann architecture, which statement describes how instructions and data are handled?

  1. Programs are stored permanently inside the control unit
  2. Instructions and data are held together in the same main memory Correct answer.
  3. Data are kept in the ALU while instructions stay in registers
  4. Every program must be stored on a separate secondary device

Explanation

Von Neumann architecture uses a single main memory to hold both program instructions and the data on which they operate. The CPU fetches an instruction from this memory, decodes it, and then fetches the required data from the same memory. This shared-memory idea is what makes the stored-program concept possible.

Question 12Introduction to Computer System and Computer Organization

Which task belongs to the Arithmetic Logic Unit (ALU) of a CPU?

  1. Carrying out arithmetic and logical operations on data Correct answer.
  2. Holding the address of the next instruction to be fetched
  3. Decoding the opcode of each instruction fetched from memory
  4. Generating the clock pulses that synchronise all CPU units

Explanation

The ALU is the part of the CPU that performs arithmetic operations such as addition and subtraction, and logical operations such as comparison and AND/OR. It works on operands supplied through registers and returns the result to a register. Control and timing functions belong to other CPU units.

Question 13Introduction to Computer System and Computer Organization

One CPU has an 8-bit data bus and another has a 16-bit data bus. What advantage does the wider data bus give the second CPU?

  1. It runs at twice the clock frequency of the other CPU
  2. It moves twice as many bits per transfer Correct answer.
  3. It contains twice as much cache memory as the other CPU
  4. It can address twice as many memory locations in main memory

Explanation

The width of the data bus is the number of bits that can be transferred between the CPU and memory or I/O in one bus operation. A 16-bit data bus therefore moves 16 bits at a time, compared with 8 bits for an 8-bit bus. Addressable memory depends on the address bus, and speed depends on the clock, not on data-bus width alone.

Question 14Introduction to Computer System and Computer Organization

Which CPU register holds the address of the next instruction to be fetched from main memory?

  1. Accumulator (AC)
  2. Program Counter (PC) Correct answer.
  3. Memory Address Register (MAR)
  4. Instruction Register (IR)

Explanation

The Program Counter stores the address of the next instruction to be fetched, and it is incremented after each fetch so that execution proceeds through the program. The MAR holds the address currently placed on the address bus, which may be an instruction or data address. The IR holds the instruction itself after it has been fetched.

Question 15Introduction to Computer System and Computer Organization

A memory chip stores each bit as charge on a tiny capacitor and must be refreshed thousands of times per second. Which memory type is described?

  1. DRAM, because it uses capacitors that leak charge Correct answer.
  2. Flash memory, because it stores charge on floating-gate transistors
  3. SRAM, because it stores each bit using a pair of cross-coupled inverters
  4. ROM, because its contents are permanent and cannot be changed

Explanation

Dynamic RAM stores each bit as charge on a capacitor, and because the charge leaks away the chip must be refreshed continuously. Static RAM instead uses flip-flop circuits and needs no refresh while power is on. Flash memory and ROM are non-volatile and do not rely on constant capacitor refreshing.

Question 16Introduction to Computer System and Computer Organization

A processor is advertised as running at 3.2 GHz. What does this figure indicate?

  1. It can store up to 3.2 billion bytes in main memory
  2. It transfers 3.2 billion bits per second on the data bus
  3. It executes exactly 3.2 billion machine instructions per second
  4. It completes 3.2 billion clock cycles per second Correct answer.

Explanation

The hertz unit measures cycles per second, so 3.2 GHz means 3.2 billion clock cycles every second. Instructions may need more than one clock cycle, so the instruction rate is not necessarily equal to the clock rate. Memory capacity and bus transfer rate are separate specifications.

Question 17Introduction to Computer System and Computer Organization

When a computer is switched on, the bootstrap loader is the first program to run. Where is it normally stored and what does it do?

  1. In RAM; it formats the secondary storage before any files are loaded
  2. On the hard disk; it installs all the device drivers during startup
  3. In the cache; it copies the BIOS instructions into the arithmetic logic unit
  4. In ROM; it runs POST and loads the operating system into RAM Correct answer.

Explanation

The bootstrap loader is stored in ROM firmware on the motherboard, so it is available immediately at power-on. It performs the power-on self-test and then locates and loads the operating system from secondary storage into main memory. This starts the machine so that normal programs can run.

Question 18Introduction to Computer System and Computer Organization

Which statement best explains why a solid-state drive (SSD) usually opens files faster than a magnetic hard disk drive (HDD)?

  1. It uses a laser beam to read pits and lands from an optical surface
  2. It keeps all frequently used files permanently inside the CPU cache
  3. Its magnetic platters rotate much faster than those inside a hard disk
  4. It has no moving head, so random access needs no seek delay Correct answer.

Explanation

An SSD stores data in flash memory and has no moving mechanical parts, so it can reach any block electronically without waiting for a read/write head to move. A magnetic HDD must position its head over the correct track and wait for the platter to rotate, which adds seek and rotational delay. This makes random access noticeably quicker on an SSD.

Question 19Introduction to Computer System and Computer Organization

A CPU takes 5 ns to access the cache and 50 ns to access main memory. On a cache miss the cache is checked first (5 ns) and then main memory is accessed (50 ns). If 90% of accesses hit the cache, what is the average memory access time?

  1. 10.0 ns Correct answer.
  2. 50.0 ns
  3. 9.5 ns
  4. 5.5 ns

Explanation

For a hit the time is 5 ns, and for a miss the time is 5 ns plus 50 ns, that is 55 ns. The average is therefore 0.9 × 5 + 0.1 × 55 = 4.5 + 5.5 = 10.0 ns. The 5 ns cache-check time must be counted on misses as well as on hits.

Question 20Introduction to Computer System and Computer Organization

A processor executes instructions through a 5-stage pipeline, and each stage takes 2 ns. Ignoring pipeline overheads, how much time is needed to complete 100 instructions?

  1. 1000 ns
  2. 208 ns Correct answer.
  3. 104 ns
  4. 200 ns

Explanation

The first instruction needs all five stages, taking 5 × 2 = 10 ns to reach the output. After that one instruction leaves the pipeline every cycle, so the remaining 99 instructions need 99 × 2 = 198 ns. The total is 10 + 198 = 208 ns.

Question 21Introduction to Computer System and Computer Organization

Which of the following is classified as system software in a computer system?

  1. A web browser used for accessing websites
  2. An operating system such as Linux Correct answer.
  3. A spreadsheet package used for payroll calculations
  4. A word processor used for creating and editing documents

Explanation

System software includes the operating system and utility programs that control hardware and provide a platform for application software. A word processor, spreadsheet and web browser are application software because they perform user-oriented tasks.

Question 22Introduction to Computer System and Computer Organization

Which of the following output devices is an impact printer?

  1. Thermal printer
  2. Laser printer
  3. Inkjet printer
  4. Dot-matrix printer Correct answer.

Explanation

An impact printer forms characters by striking an inked ribbon against the paper, and a dot-matrix printer works in exactly this way. Laser, inkjet and thermal printers form images without striking the paper, so they are non-impact printers.

Question 23Introduction to Computer System and Computer Organization

How does a compiler differ from an interpreter when translating a high-level language program?

  1. A compiler runs on the same computer only, while an interpreter can run on any computer.
  2. A compiler executes the source program directly without producing any intermediate form, while an interpreter always produces an object file.
  3. A compiler translates the whole program before execution, while an interpreter translates and executes line by line. Correct answer.
  4. A compiler is used only for assembly language, while an interpreter is used only for machine language.

Explanation

A compiler scans the entire source program and produces object code before the program is run. An interpreter translates one statement at a time and immediately executes it, stopping if an error is found.

Question 24Introduction to Computer System and Computer Organization

In the CPU, which pair of registers is directly involved when the processor reads a word from main memory?

  1. The program counter and the accumulator register
  2. The instruction register together with the processor status register
  3. The stack pointer and the index register
  4. The memory address register and the memory buffer register Correct answer.

Explanation

During a memory read, the address of the required location is placed in the Memory Address Register and the data fetched is placed in the Memory Buffer Register. The Program Counter holds the address of the next instruction, while the Instruction Register holds the instruction currently being executed.

Question 25Introduction to Computer System and Computer Organization

Which bus in a computer system carries signals such as memory read, memory write and interrupt request?

  1. Data bus
  2. Power bus
  3. Control bus Correct answer.
  4. Address bus

Explanation

The control bus carries command and timing signals such as memory read, memory write and interrupt request between the CPU and other units. The address bus carries location addresses and the data bus carries the actual data.

Question 26Introduction to Computer System and Computer Organization

What is the main purpose of using virtual memory in a computer?

  1. To connect the CPU directly to the printer without using any cable
  2. To increase the physical storage capacity of the hard disk permanently by adding more platters
  3. To allow programs larger than the available physical RAM to run by using disk space as an extension of main memory Correct answer.
  4. To store the BIOS permanently on the motherboard so that its contents can never be changed or erased by any program running on the computer

Explanation

Virtual memory uses part of secondary storage as an extension of main memory, so pages not currently needed can be moved to disk. This lets a program larger than physical RAM run, although access to disk pages is slower than access to RAM.

Question 27Introduction to Computer System and Computer Organization

A processor runs at a clock frequency of 2 GHz and executes, on average, one instruction in 4 clock cycles. What is its approximate speed in millions of instructions per second (MIPS)?

  1. 2000 MIPS
  2. 8 MIPS
  3. 1000 MIPS
  4. 500 MIPS Correct answer.

Explanation

At 2 GHz the processor completes 2 × 10^9 clock cycles per second. With an average of 4 cycles per instruction, it executes 2 × 10^9 ÷ 4 = 5 × 10^8 instructions per second, which is 500 MIPS.

Question 28Introduction to Computer System and Computer Organization

Which statement best explains the advantage of interrupt-driven I/O over programmed polling?

  1. The CPU can do other work instead of repeatedly checking the device status until the device sends a signal. Correct answer.
  2. The CPU transfers data without any involvement of the device controller or the system bus at any stage of the operation.
  3. The operating system is completely bypassed during every data transfer between the device and the memory.
  4. The device can write directly into the CPU registers without using the bus or main memory.

Explanation

With polling, the CPU repeatedly checks a device status flag and wastes cycles while the device is not ready. An interrupt tells the CPU when the device needs service, so the CPU can carry out other useful work in the meantime.

Question 29Number Systems and Boolean Algebra

The binary number 110101₂ is equivalent to which decimal number?

  1. 51
  2. 53 Correct answer.
  3. 43
  4. 55

Explanation

Convert by summing the place values where bits are 1: 1×32 + 1×16 + 0×8 + 1×4 + 0×2 + 1×1. This gives 32 + 16 + 4 + 1 = 53. Each position corresponds to a power of 2 starting from 2⁰ on the right.

Question 30Number Systems and Boolean Algebra

The decimal number 45 is represented in binary as which of the following?

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

Explanation

Write 45 as a sum of powers of 2: 45 = 32 + 8 + 4 + 1. Reading a 6-bit pattern from the 32-place down to the 1-place gives 101101₂. Checking the values: 32 + 0 + 8 + 4 + 0 + 1 = 45.

Question 31Number Systems and Boolean Algebra

In Boolean algebra, which expression is equal to A + A'?

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

Explanation

The complement law states that a variable ORed with its complement always yields 1, because either A is true or A' is true, but not both. This is written as A + A' = 1. It is a fundamental identity used when simplifying logic expressions.

Question 32Number Systems and Boolean Algebra

The octal number 357₈ is equivalent to which hexadecimal number?

  1. DF
  2. EE
  3. EF Correct answer.
  4. F0

Explanation

Convert octal 357₈ to decimal first: 3×64 + 5×8 + 7×1 = 192 + 40 + 7 = 239. Then convert 239 to hexadecimal by dividing by 16: 239 = 14×16 + 15, and 14 = E, 15 = F, giving EF₁₆. A shortcut is to group binary bits: 357₈ = 011 101 111₂ = 11101111₂ = EF₁₆.

Question 33Number Systems and Boolean Algebra

The 2's complement of the 8-bit binary number 01011010 is which of the following?

  1. 01011011
  2. 11011010
  3. 10100101
  4. 10100110 Correct answer.

Explanation

The 2's complement is found by inverting all bits and then adding 1 to the least significant bit. For 01011010, the 1's complement is 10100101, and adding 1 gives 10100110. This representation is widely used to store negative numbers in computers.

Question 34Number Systems and Boolean Algebra

According to De Morgan's theorem, the expression (A + B)' is equivalent to which of the following?

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

Explanation

De Morgan's theorem states that the complement of a sum equals the product of the complements: (A + B)' = A' · B'. The dual form is (A · B)' = A' + B'. These laws allow NAND and NOR gates to implement any logic function.

Question 35Number Systems and Boolean Algebra

Subtracting 1010₂ from 1101₂ gives which binary result?

  1. 0101
  2. 0001
  3. 0011 Correct answer.
  4. 0111

Explanation

In decimal, 1101₂ is 13 and 1010₂ is 10, so the difference is 3, which is 0011₂. Using 2's complement: the 2's complement of 1010 is 0110, and 1101 + 0110 = 1 0011; discarding the final carry leaves 0011₂.

Question 36Number Systems and Boolean Algebra

The Boolean expression A·B + A·B' + A'·B simplifies to which of the following?

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

Explanation

The first two terms simplify by the distributive law: A·B + A·B' = A(B + B') = A·1 = A. Then A + A'·B reduces to A + B by the absorption law X + X'Y = X + Y. Therefore the minimal expression is A + B.

Question 37Number Systems and Boolean Algebra

The Boolean function F(A,B,C) = Σm(0,1,2,5,6,7) has which minimal sum-of-products expression?

  1. A'B' + BC' + AC Correct answer.
  2. A'B' + B'C + AC
  3. A'B' + BC' + AB
  4. A'B' + AB + AC

Explanation

Plotting the minterms 0, 1, 2, 5, 6 and 7 on a 3-variable Karnaugh map gives three groups: A'B' covers m0 and m1, BC' covers m2 and m6, and AC covers m5 and m7. These prime implicants together cover every 1 in the map and cannot be combined further. Hence the minimal SOP expression is A'B' + BC' + AC.

Question 38Number Systems and Boolean Algebra

What is the range of signed integers that can be represented in 8-bit 2's complement form?

  1. -127 to +127
  2. 0 to 255
  3. -128 to +127 Correct answer.
  4. -128 to +128

Explanation

In 8-bit 2's complement, the most significant bit is the sign bit, leaving 7 bits for magnitude. The most negative value is -2⁷ = -128, while the most positive value is +2⁷ - 1 = +127. Therefore the range is -128 to +127.

Question 39Number Systems and Boolean Algebra

In the hexadecimal number system, which symbol represents the decimal value 12?

  1. F
  2. A
  3. C Correct answer.
  4. B

Explanation

Hexadecimal uses sixteen symbols: 0–9 for values zero to nine and A–F for ten to fifteen. Therefore decimal 12 maps to the hexadecimal digit C.

Question 40Number Systems and Boolean Algebra

The binary number 101101₂ is equivalent to which octal number?

  1. 101₈
  2. 45₈
  3. 65₈
  4. 55₈ Correct answer.

Explanation

Group the binary digits into sets of three from the right: 101 101. Each group 101₂ equals decimal 5, so the octal result is 55₈.

Question 41Number Systems and Boolean Algebra

In Boolean algebra, the expression A + A·B simplifies to which of the following?

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

Explanation

The absorption law states that A + A·B = A·(1 + B) = A, because 1 + B is always 1. Thus the term A·B is absorbed by A.

Question 42Number Systems and Boolean Algebra

The sum of the binary numbers 1011₂ and 1101₂ is which of the following?

  1. 11000₂ Correct answer.
  2. 10110₂
  3. 10010₂
  4. 11010₂

Explanation

Adding 1011₂ (11) and 1101₂ (13) gives decimal 24. Decimal 24 is written as 11000₂, so the binary sum is 11000₂.

Question 43Number Systems and Boolean Algebra

The 1's complement of the 8-bit binary number 10101100 is which of the following?

  1. 11010011₂
  2. 01010011₂ Correct answer.
  3. 10101101₂
  4. 01010100₂

Explanation

The 1's complement is formed by changing every 0 to 1 and every 1 to 0. Inverting 10101100 bit by bit gives 01010011.

Question 44Number Systems and Boolean Algebra

Which Boolean expression is equivalent to A ⊕ B?

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

Explanation

The XOR operation A ⊕ B is true only when the two inputs differ. This condition is written as A'B + AB', where exactly one input is complemented in each product term.

Question 45Number Systems and Boolean Algebra

The Boolean expression (A + B)·(A + C) simplifies to which of the following?

  1. A·B·C
  2. A + BC Correct answer.
  3. A + B + C
  4. AB + AC

Explanation

Expanding gives (A + B)(A + C) = AA + AC + AB + BC. Since AA = A, the expression becomes A(1 + C + B) + BC = A + BC by absorption.

Question 46Number Systems and Boolean Algebra

What is the minimum number of bits required to represent the decimal number 200 in unsigned binary?

  1. 7 bits
  2. 8 bits Correct answer.
  3. 6 bits
  4. 9 bits

Explanation

An unsigned binary number with n bits can represent values from 0 to 2^n − 1. Since 2^7 = 128 is too small and 2^8 = 256 covers 200, eight bits are required.

Question 47Number Systems and Boolean Algebra

The binary number 101.101₂ is equivalent to which decimal value?

  1. 5.75
  2. 5.625 Correct answer.
  3. 5.125
  4. 5.25

Explanation

For 101.101₂, the integer part is 4 + 1 = 5. The fractional part is 1/2 + 0/4 + 1/8 = 0.5 + 0.125 = 0.625, so the value is 5.625.

Question 48Number Systems and Boolean Algebra

For the Boolean function F(A,B,C) = Σm(1,3,5,7), which is the minimal sum-of-products expression?

  1. C Correct answer.
  2. A
  3. A ⊕ B
  4. B

Explanation

All four minterms 1, 3, 5, and 7 have C = 1, while A and B take every combination. Therefore the cell group covers the entire C variable, and the minimal SOP is simply C.

Question 49Number Systems and Boolean Algebra

The hexadecimal number 2F₁₆ is equivalent to which decimal value?

  1. 215
  2. 31
  3. 45
  4. 47 Correct answer.

Explanation

Each hexadecimal place carries a weight that is a power of 16, so 2F₁₆ = 2 × 16¹ + 15 × 16⁰ (F stands for 15). This gives 32 + 15 = 47, so the decimal equivalent is 47.

Question 50Number Systems and Boolean Algebra

In 8-bit 2's complement representation, the bit pattern 11110000 represents which decimal value?

  1. 240
  2. -15
  3. -16 Correct answer.
  4. -112

Explanation

The leftmost bit is 1, so the number is negative. Taking the 2's complement of 11110000 gives 00010000, which equals 16, so the stored pattern represents -16.