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BSEB Inter Computer Science study materials
BSEB Inter Computer Science study resources

BSEB Inter Computer Science practice questions

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Question 1Computer Fundamentals, Number Systems and Boolean Logic

How many distinct digit symbols does the octal number system use, and which ones are they?

  1. Ten symbols, 0 through 9
  2. Eight symbols, 0 through 7 Correct answer.
  3. Sixteen symbols, 0 through 9 plus A through F
  4. Two symbols, 0 and 1

Explanation

Octal is a base-8 positional system, so it is built from exactly eight digit symbols: 0, 1, 2, 3, 4, 5, 6 and 7. The symbol 8 never appears in an octal number, because a count of eight is written as 10 (one group of eight plus zero units). Each place value is a power of 8.

Question 2Computer Fundamentals, Number Systems and Boolean Logic

In Boolean algebra, what is the value of the expression A + A′ for any Boolean variable A?

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

Explanation

This is the complement law: a variable ORed with its own complement always gives 1. If A = 0 then A′ = 1 and 0 + 1 = 1; if A = 1 then A′ = 0 and 1 + 0 = 1. The result is therefore independent of the value of A.

Question 3Computer Fundamentals, Number Systems and Boolean Logic

Which of the following storage or memory units is volatile, that is, it loses its contents when the power supply is switched off?

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

Explanation

RAM (Random Access Memory) is the main working memory of a computer and is volatile: every stored bit disappears when power is removed. ROM, hard disks and flash drives are non-volatile because they retain data without a continuous power supply. This is why unsaved work held in RAM is lost during a power failure.

Question 4Computer Fundamentals, Number Systems and Boolean Logic

What is the decimal equivalent of the binary number 1101₂?

  1. 14
  2. 11
  3. 13 Correct answer.
  4. 26

Explanation

Expand the binary number using place values 2³, 2², 2¹ and 2⁰: 1×8 + 1×4 + 0×2 + 1×1. This gives 8 + 4 + 0 + 1 = 13. The bits in positions three and two contribute, the 2s bit contributes nothing, and the units bit contributes one.

Question 5Computer Fundamentals, Number Systems and Boolean Logic

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

  1. 215
  2. 52
  3. 47 Correct answer.
  4. 31

Explanation

In hexadecimal, F stands for decimal 15. Evaluate as 2×16¹ + 15×16⁰ = 32 + 15 = 47. Treating the digits as decimal (2 and 15 read literally) or failing to convert F is the usual source of error.

Question 6Computer Fundamentals, Number Systems and Boolean Logic

The Boolean expression F = A + AB simplifies to which of the following?

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

Explanation

Apply the absorption law, A + AB = A(1 + B) = A·1 = A. The term AB can never make the output 1 unless A is already 1, so B has no effect on the result. Absorption is one of the standard rules used to minimise logic expressions before building a circuit.

Question 7Computer Fundamentals, Number Systems and Boolean Logic

Using 4-bit two's complement representation, the decimal value −6 is written as:

  1. 1001
  2. 1010 Correct answer.
  3. 1110
  4. 0110

Explanation

First write +6 in 4 bits as 0110. Invert all bits to get the one's complement 1001, then add 1, giving 1010. Checking back, 1010 has a place value of −8 + 2 = −6, which confirms the answer.

Question 8Computer Fundamentals, Number Systems and Boolean Logic

In a half adder built from logic gates, the SUM output for inputs A and B is produced by which operation?

  1. A XOR B Correct answer.
  2. A XNOR B
  3. A OR B
  4. A AND B

Explanation

A half adder adds two single bits. The sum is 1 only when the inputs differ, which is exactly the exclusive-OR function, so SUM = A ⊕ B. The carry output is separately produced by A AND B, which becomes 1 only when both inputs are 1.

Question 9Computer Fundamentals, Number Systems and Boolean Logic

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

  1. 8 bits Correct answer.
  2. 9 bits
  3. 10 bits
  4. 7 bits

Explanation

With n bits an unsigned number can range from 0 to 2ⁿ − 1. Seven bits cover only 0 to 127, which is too small, while eight bits cover 0 to 255, which includes 200. Therefore 8 bits is the minimum, and 200 is written as 11001000.

Question 10Computer Fundamentals, Number Systems and Boolean Logic

The Boolean expression AB + A′B + AB′ simplifies to which of the following?

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

Explanation

Group the first two terms: AB + A′B = B(A + A′) = B. Then combine this with the remaining term using absorption: B + AB′ = B + A. The final minimised expression is therefore A + B.

Question 11Computer Fundamentals, Number Systems and Boolean Logic

What is the octal equivalent of the binary number 101110₂?

  1. 65₈
  2. 56₈ Correct answer.
  3. 46₈
  4. 74₈

Explanation

Group the binary digits in sets of three starting from the right: 101 110. Each group converts directly to one octal digit, since 101₂ = 5 and 110₂ = 6, giving 56₈.

Question 12Computer Fundamentals, Number Systems and Boolean Logic

Which part of the CPU performs arithmetic operations such as addition and Boolean operations such as AND?

  1. Memory Address Register
  2. Control Unit
  3. Arithmetic Logic Unit Correct answer.
  4. Program Counter

Explanation

The Arithmetic Logic Unit (ALU) is the CPU section that executes arithmetic operations such as addition and subtraction and logical operations such as AND, OR and NOT. The control unit only directs and coordinates, while registers such as the program counter hold addresses or instructions.

Question 13Computer Fundamentals, Number Systems and Boolean Logic

For a 2-input NOR gate, the output is HIGH only when:

  1. the two inputs are different
  2. both inputs are HIGH
  3. both inputs are LOW Correct answer.
  4. at least one input is HIGH

Explanation

A NOR gate is an OR gate followed by an inverter, so its output is the complement of A + B. The OR output is 0 only when both inputs are 0, therefore the NOR output is HIGH only for the input combination 0,0.

Question 14Computer Fundamentals, Number Systems and Boolean Logic

The range of decimal integers that can be stored in an 8-bit signed two's complement register is:

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

Explanation

In an n-bit two's complement system the representable range is −2^(n−1) to +2^(n−1) − 1. For n = 8 this gives −128 to +127, and the all-zero pattern represents 0 while 10000000 represents −128.

Question 15Computer Fundamentals, Number Systems and Boolean Logic

According to De Morgan's theorem, the complement of the expression A · B is:

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

Explanation

De Morgan's theorem states that the complement of a product equals the sum of the complements, so (A · B)′ = A′ + B′. The theorem is proved by comparing the truth tables of both sides.

Question 16Computer Fundamentals, Number Systems and Boolean Logic

The Boolean expression (A + B)(A + C) simplifies to:

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

Explanation

Expanding the product gives A·A + A·C + B·A + B·C = A + AC + AB + BC. Using the absorption law A + AB = A, the first three terms reduce to A, leaving A + BC.

Question 17Computer Fundamentals, Number Systems and Boolean Logic

Which system bus carries the binary address of the memory location that the CPU wants to read or write?

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

Explanation

The address bus is a one-way bus that carries the address generated by the CPU to memory or I/O devices. The data bus carries the actual contents in both directions, and the control bus carries read/write and timing signals.

Question 18Computer Fundamentals, Number Systems and Boolean Logic

The decimal number 47 written in 8421 BCD is:

  1. 0010 1111
  2. 0100 0111 Correct answer.
  3. 0111 0100
  4. 0101 0111

Explanation

In 8421 BCD each decimal digit is coded separately in four bits. The digit 4 becomes 0100 and the digit 7 becomes 0111, so 47 is written as 0100 0111.

Question 19Computer Fundamentals, Number Systems and Boolean Logic

The Boolean function F = A′BC + AB′C + ABC′ + ABC is 1 whenever at least two inputs are 1. It simplifies to:

  1. A′B + B′C + A′C
  2. A′B′C′ + ABC
  3. A + B + C + ABC
  4. AB + BC + CA Correct answer.

Explanation

Combine the term ABC with each of the other three terms: ABC + ABC′ = AB, ABC + AB′C = AC and ABC + A′BC = BC. Adding these gives F = AB + AC + BC, the majority function, which is 1 whenever at least two inputs are 1.

Question 20Computer Fundamentals, Number Systems and Boolean Logic

The 8-bit two's complement representation of the decimal number −25 is:

  1. 11100110
  2. 00011001
  3. 11100111 Correct answer.
  4. 10011001

Explanation

Write +25 in 8-bit binary as 00011001, then invert all bits to get 11100110 and add 1 to the least significant bit. The result is 11100111, which represents −25 in two's complement.

Question 21Computer Fundamentals, Number Systems and Boolean Logic

Which number system is used internally by digital computers because it has only two states?

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

Explanation

Binary uses only two symbols, 0 and 1, which map directly to the two voltage states used by digital circuits. Decimal, octal and hexadecimal require more than two digit symbols, so they are not the native internal representation.

Question 22Computer Fundamentals, Number Systems and Boolean Logic

Which logic gate produces an output that is the inverse of its single input?

  1. NOT gate Correct answer.
  2. XOR gate
  3. AND gate
  4. OR gate

Explanation

A NOT gate has one input and produces the complement of that input: a LOW input gives HIGH and a HIGH input gives LOW. AND, OR and XOR gates each require two or more inputs and do not simply invert a single value.

Question 23Computer Fundamentals, Number Systems and Boolean Logic

Which of these is a secondary storage device?

  1. RAM
  2. CPU register
  3. Cache memory
  4. Hard disk Correct answer.

Explanation

Secondary storage holds data permanently or semi-permanently and is not directly executed by the CPU. A hard disk is secondary storage, while RAM, cache and CPU registers are primary or internal storage used for active processing.

Question 24Computer Fundamentals, Number Systems and Boolean Logic

The decimal fraction 0.625 is written in binary as:

  1. 0.100₂
  2. 0.110₂
  3. 0.101₂ Correct answer.
  4. 0.011₂

Explanation

Multiply the fraction by 2 repeatedly: 0.625×2=1.25, record 1; 0.25×2=0.5, record 0; 0.5×2=1.0, record 1. Reading the integer parts gives 0.101₂.

Question 25Computer Fundamentals, Number Systems and Boolean Logic

Perform the binary subtraction: 1001₂ − 0110₂. The result is:

  1. 0111₂
  2. 0011₂ Correct answer.
  3. 0010₂
  4. 0101₂

Explanation

1001₂ equals 9 and 0110₂ equals 6, so the difference is 3, written as 0011₂ in four bits. Direct bit subtraction with borrow gives the same result.

Question 26Computer Fundamentals, Number Systems and Boolean Logic

In Boolean algebra, the expression A(A + B) simplifies to:

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

Explanation

Expand by distributivity: A(A+B)=A·A+A·B=A+AB. Then apply absorption, A+AB=A, so the expression reduces to A for all values of B.

Question 27Computer Fundamentals, Number Systems and Boolean Logic

A 3-input AND gate gives a HIGH output only when:

  1. exactly two inputs are HIGH
  2. all inputs are LOW
  3. at least one input is HIGH
  4. all inputs are HIGH Correct answer.

Explanation

An AND gate outputs HIGH only when every input is HIGH; if any input is LOW, the output is LOW. For three inputs, the only HIGH-output condition is A=B=C=1.

Question 28Computer Fundamentals, Number Systems and Boolean Logic

The binary number 1110 1010₂ is equal to which hexadecimal value?

  1. E9₁₆
  2. EA₁₆ Correct answer.
  3. AE₁₆
  4. FA₁₆

Explanation

Split the 8-bit binary number into two 4-bit groups: 1110₂ = E₁₆ and 1010₂ = A₁₆. Concatenating the two hex digits gives EA₁₆.

Question 29Computer Fundamentals, Number Systems and Boolean Logic

Which expression is the Boolean XOR of A and B using only AND, OR and NOT?

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

Explanation

XOR is HIGH when exactly one input is HIGH, which is captured by A′B + AB′. The other listed forms represent XNOR, OR, or the condition where both inputs are 0.

Question 30Computer Fundamentals, Number Systems and Boolean Logic

An unsigned 4-bit register stores its maximum value. What is that value, and what results if 1 is added to it?

  1. 16 and then 17, since no overflow
  2. 15 and then 0, because of overflow Correct answer.
  3. 15 and then 16, since range extends
  4. 14 and then 15, because 4 bits end at 14

Explanation

Four unsigned bits can represent 0000₂ through 1111₂, so the maximum is 15. Adding 1 produces 10000₂, which needs five bits; the 4-bit register keeps 0000₂ and sets an overflow indication.

Question 31Computer Organisation: Hardware, Software and Memory

A student switches off a computer and later finds that the program she typed before shutting down is gone, although the BIOS setup instructions are still available at start-up. Which statement explains this observation?

  1. RAM is volatile and loses its contents when power is removed, whereas ROM retains its contents. Correct answer.
  2. Both RAM and ROM lose their contents, but ROM is reloaded from the hard disk at start-up.
  3. RAM retains its contents permanently, whereas ROM is erased whenever the machine is switched off.
  4. Both RAM and ROM retain their contents, but the typed program was stored in ROM by mistake.

Explanation

RAM is a volatile semiconductor memory: it needs a continuous power supply, so whatever the user was working on disappears when the machine is switched off. ROM is non-volatile and is programmed during manufacture or by a special process, so the firmware needed at start-up is still present. This is why the typed program is lost while the BIOS instructions survive.

Question 32Computer Organisation: Hardware, Software and Memory

While a program is running, the CPU must know the address of the next instruction to be fetched from main memory. Which register holds this address?

  1. Instruction register
  2. Program counter Correct answer.
  3. Stack pointer
  4. Accumulator

Explanation

The program counter (PC) stores the address of the next instruction to be fetched, and it is automatically incremented after each fetch so that execution proceeds in sequence. The accumulator holds data being processed, the instruction register holds the instruction currently being decoded, and the stack pointer marks the top of the stack.

Question 33Computer Organisation: Hardware, Software and Memory

Software is commonly divided into system software and application software. Which of the following belongs to the category of system software?

  1. An image editor used to retouch photographs
  2. A spreadsheet package used for accounts
  3. An operating system that manages hardware and programs Correct answer.
  4. A word processor used to type a project report

Explanation

System software runs the machine itself and provides the platform on which user tasks are performed; the operating system, language translators and utility programs all belong to this class. Word processors, spreadsheets and image editors are application software because they perform particular tasks for the end user.

Question 34Computer Organisation: Hardware, Software and Memory

A program contains a small loop of instructions that is executed again and again. Which memory unit is provided in a computer specifically to exploit this repeated access and reduce the average time the CPU waits for instructions?

  1. Magnetic disk storage
  2. Flash memory
  3. Virtual memory
  4. Cache memory Correct answer.

Explanation

Cache is a small, very fast memory placed close to the CPU that holds recently or frequently used instructions and data. Because the loop is executed repeatedly, its instructions are likely to be found in cache on later passes, which greatly reduces the average access time. This behaviour is an example of the principle of locality of reference.

Question 35Computer Organisation: Hardware, Software and Memory

A chip whose contents can be erased by exposing a quartz window on the package to ultraviolet light and then reprogrammed with a device programmer is known as which type of memory?

  1. PROM
  2. Mask ROM
  3. EPROM Correct answer.
  4. EEPROM

Explanation

Erasable Programmable Read-Only Memory (EPROM) is programmed electrically but erased by ultraviolet light shining through a small quartz window, after which it can be programmed again. EEPROM is erased electrically, PROM can be written only once by the user, and mask ROM is programmed during manufacture and cannot be altered afterwards.

Question 36Computer Organisation: Hardware, Software and Memory

Which sequence arranges the following memory units in order from fastest access to slowest access?

  1. Magnetic disk, main memory, cache
  2. Cache, magnetic disk, main memory
  3. Main memory, cache, magnetic disk
  4. Cache, main memory, magnetic disk Correct answer.

Explanation

The memory hierarchy places the fastest and most expensive devices nearest the CPU. Cache is built from very fast static circuits, main memory is slower dynamic RAM, and magnetic disk involves mechanical movement of heads and rotation of platters, making it the slowest of the three.

Question 37Computer Organisation: Hardware, Software and Memory

Within the CPU, which unit fetches each instruction, decodes it and issues the timing and control signals that make the other units carry it out?

  1. Arithmetic logic unit
  2. Secondary storage unit
  3. Control unit Correct answer.
  4. Main memory unit

Explanation

The control unit directs the operation of the whole processor: it fetches instructions, decodes them and generates the control signals that coordinate the ALU, registers and memory during the fetch-decode-execute cycle. The arithmetic logic unit performs the actual calculations, while memory units only store data and instructions.

Question 38Computer Organisation: Hardware, Software and Memory

In an instruction such as ADD 25, the value 25 is held inside the instruction itself rather than being the address of an operand. Which addressing mode is being used?

  1. Direct addressing
  2. Register addressing
  3. Indirect addressing
  4. Immediate addressing Correct answer.

Explanation

Immediate addressing places the operand value directly in the instruction, so no extra memory reference is needed to obtain it. In direct addressing the instruction gives the address of the operand, in indirect addressing it gives the address of an address, and in register addressing the operand sits in a named register.

Question 39Computer Organisation: Hardware, Software and Memory

A running program tries to read a page that is part of its logical address space but is not presently loaded in main memory. What does the operating system normally do in this situation?

  1. It terminates the program immediately and reports a permanent hardware failure.
  2. It expands the physical capacity of the main memory chips to fit the page.
  3. It copies the entire program into the cache so that all future references hit there.
  4. It brings the required page in from secondary storage into a free main memory frame. Correct answer.

Explanation

This event is a page fault. The operating system takes control, finds the required page in the swap area on secondary storage, loads it into a free frame of main memory and then restarts the interrupted instruction so that the reference can succeed. If no frame is free, a page replacement policy chooses a victim page to write back first.

Question 40Computer Organisation: Hardware, Software and Memory

A hard disk must transfer a large block of data to main memory, and the designers wish to avoid the CPU being occupied for every byte moved. Which facility is intended for this purpose?

  1. Direct Memory Access Correct answer.
  2. Polling of the device status register
  3. Spooling of output jobs
  4. Interrupt vectoring

Explanation

Direct Memory Access uses a dedicated controller that takes over the system bus and moves blocks of data between the device and main memory without the CPU handling each byte. The CPU merely sets up the transfer and is informed by an interrupt when the whole block is complete, so it remains free for other work.

Question 41Computer Organisation: Hardware, Software and Memory

Which CPU component carries out arithmetic operations such as addition and logical operations such as AND?

  1. The program counter
  2. The arithmetic logic unit Correct answer.
  3. The memory address register
  4. The control unit

Explanation

The arithmetic logic unit, or ALU, is the combinational circuit inside the CPU that performs arithmetic and logical operations on operands supplied from registers. The control unit directs the operation, but it does not itself perform the addition or AND operation.

Question 42Computer Organisation: Hardware, Software and Memory

What is the main purpose of an operating system in a computer system?

  1. It permanently stores files when the power is switched off
  2. It converts a high-level source program into machine code
  3. It manages hardware resources and provides services to programs Correct answer.
  4. It performs arithmetic and logic operations inside the CPU

Explanation

An operating system is system software that controls hardware resources such as memory, CPU time and input/output devices, and it provides common services on which application programs rely. It schedules processes and manages files, but it is not the component that performs arithmetic inside the CPU.

Question 43Computer Organisation: Hardware, Software and Memory

Which system bus carries memory addresses from the CPU to main memory during a read or write operation?

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

Explanation

The address bus is a one-way bus that carries the address selected by the CPU to memory or an input/output device. The data bus carries the actual contents, while the control bus carries signals such as read and write.

Question 44Computer Organisation: Hardware, Software and Memory

A byte-addressable memory is connected to a CPU with 16 address lines. What is the maximum memory capacity that the CPU can directly address?

  1. 48 KB
  2. 32 KB
  3. 64 KB Correct answer.
  4. 16 KB

Explanation

With 16 address lines, the CPU can form 2^16 different addresses. In a byte-addressable memory this gives 65,536 bytes, which equals 64 KB.

Question 45Computer Organisation: Hardware, Software and Memory

Why does adding cache memory usually improve CPU performance?

  1. It increases the storage capacity of the hard disk
  2. It replaces the need for secondary storage completely
  3. It makes main memory non-volatile and permanent
  4. It keeps frequently used data close to the CPU Correct answer.

Explanation

Cache is a small, fast memory placed between the CPU and main memory. It exploits locality of reference by holding recently or frequently used instructions and data, so the CPU spends less time waiting for slower main memory.

Question 46Computer Organisation: Hardware, Software and Memory

Which statement correctly distinguishes SRAM from DRAM?

  1. SRAM uses capacitors and must be refreshed constantly
  2. SRAM uses flip-flops and is commonly used for cache memory Correct answer.
  3. DRAM uses flip-flops and is faster than SRAM
  4. DRAM is non-volatile while SRAM loses data when power is off

Explanation

Static RAM stores each bit in a flip-flop, so it holds its data as long as power is supplied and does not need periodic refreshing. Its speed and cost make it suitable for cache, while dynamic RAM uses capacitors and needs refresh cycles.

Question 47Computer Organisation: Hardware, Software and Memory

A student writes a program in C and needs the source code translated into machine-level object code. Which software tool performs this translation?

  1. Linker
  2. Debugger
  3. Compiler Correct answer.
  4. Assembler

Explanation

A compiler translates a program written in a high-level language such as C into machine-level object code. The linker then combines object files and library routines into a final executable.

Question 48Computer Organisation: Hardware, Software and Memory

After an instruction has been fetched from main memory, in which CPU register is it held while it is decoded?

  1. Memory address register (MAR)
  2. Accumulator (ACC)
  3. Program counter (PC)
  4. Instruction register (IR) Correct answer.

Explanation

The instruction register receives the fetched instruction and holds it while the control unit decodes it. The program counter, by contrast, holds the address of the next instruction to be fetched.

Question 49Computer Organisation: Hardware, Software and Memory

A processor uses 32-bit logical addresses and a page size of 4 KB. How many entries are required in a single-level page table for one process?

  1. 2^12 entries
  2. 2^20 entries Correct answer.
  3. 2^10 entries
  4. 2^32 entries

Explanation

A 4 KB page size equals 2^12 bytes, so the page offset uses 12 bits. The remaining 20 bits of the 32-bit logical address form the page number, giving 2^20 page-table entries.

Question 50Computer Organisation: Hardware, Software and Memory

A direct-mapped cache has 8 cache lines, numbered 0 to 7. If main-memory block 13 is loaded into the cache, which cache line will it occupy?

  1. Line 13
  2. Line 3
  3. Line 8
  4. Line 5 Correct answer.

Explanation

In a direct-mapped cache, the target line is found by taking the block number modulo the number of cache lines. Here 13 mod 8 equals 5, so block 13 maps to line 5.