Computer Network Questions and Answers

Q: A JK flip-flop toggles its output when both J and K inputs are HIGH.

Correct answer: TrueThe statement is true, and it is the feature that makes the JK flip-flop the most versatile of the four types. Its behaviour on a clock edge is: J = 0, K = 0 holds the previous state; J = 0, K = 1 resets to 0; J = 1, K = 0 sets to 1; and J = 1, K = 1 toggles, so the output becomes the complement of what it was. The toggle case is precisely what the SR flip-flop cannot do. In an SR flip-flop, setting both inputs high is a forbidden condition, because it drives both outputs to the same level and leaves the next state indeterminate when the inputs are released. The JK resolves that by feeding the outputs back into the input gating, turning the invalid case into a useful one. Tying J and K together to a permanent 1 gives a T flip-flop, which toggles on every clock pulse - and that is the building block of binary counters, since each stage divides the frequency by two.

Q: Minimum number of bits required to represent B is

Correct answer: 3Three bits distinguish eight values, which is the smallest power of two large enough for the symbol set in question: \( 2^{2}=4 \) is too few and \( 2^{3}=8 \) suffices.

Q: A latch is level-triggered while a flip-flop is edge-triggered.

Correct answer: TrueA latch responds to its inputs for as long as the enable line is active, whereas a flip-flop samples only at the rising or falling edge of the clock. Edge triggering is what keeps a synchronous circuit’s stages from racing ahead of each other.

Q: What can happen at a Token Ring station

Correct answer: All of theseEvery station on a Token Ring acts as a repeater: it examines the destination address to see whether the frame is for it, regenerates the signal, and passes the frame on round the ring.

Q: Which number system is used internally by digital computers?

Correct answer: BinaryDigital computers work internally in binary, base 2, using only the digits 0 and 1. The reason is physical rather than mathematical. A circuit can distinguish two voltage levels reliably and cheaply - on or off, high or low - and that reliability degrades quickly if more levels must be told apart. Two states also map directly onto the switching behaviour of a transistor and onto the true and false of Boolean algebra, which is what makes logic gates possible. Octal and hexadecimal are used by people rather than by machines, as compact ways of writing binary: each octal digit stands for exactly three bits and each hexadecimal digit for exactly four, so conversion is done by grouping rather than by division. A byte such as 11010110 becomes D6 in hexadecimal at a glance. Decimal is what humans use, and converting between it and binary requires actual arithmetic, which is why it is not used internally.

Q: The number of distinct states in a 3-bit binary counter is

Correct answer: 8A counter with \( n \) bits passes through \( 2^{n} \) distinct states, so with three bits \[ 2^{3} = 8, \] running from 000 to 111 - decimal 0 to 7 - before returning to 000. That return is why such a device is called a modulus-8 counter, and why its highest output is the clock frequency divided by eight. Counters are therefore used as frequency dividers as often as they are used to count. The same relation works in reverse: a counter of modulus \( N \) needs the smallest \( n \) for which \( 2^{n} \ge N \). A decade counter of modulus 10 needs four flip-flops, and the six surplus states are removed by feedback that clears the counter when it reaches ten. It is the identical arithmetic that fixes the number of select lines on a multiplexer, the outputs of a decoder and the address lines of a memory - one relation worth being fluent in.

Q: In an AND gate, the output is HIGH only when all inputs are HIGH.

Correct answer: TrueThe statement is true. An AND gate outputs 1 only when every one of its inputs is 1; if any input is 0 the output is 0. Its Boolean expression is \( Y = A \cdot B \). Its truth table for two inputs runs: 0,0 gives 0; 0,1 gives 0; 1,0 gives 0; 1,1 gives 1. Only the last row gives 1. A useful way to remember it is that AND behaves exactly like ordinary multiplication on the digits 0 and 1, which is why the operation is written with a dot and often called the logical product. OR is correspondingly called the logical sum, though \( 1 + 1 = 1 \) breaks the analogy there. The AND gate is also used as an enable: holding one input at 1 lets the other pass through unchanged, and holding it at 0 blocks the signal. That is how a clock is gated on and off in practice.

Q: Non-polling system is

Correct answer: TDMAIn TDMA each station has its own time slot and transmits in it without being asked, so no station has to be polled. Stop-and-wait and continuous ARQ are error-control schemes rather than access methods.

Q: Which of these is an example of non-volatile storage?

Correct answer: Hard diskA hard disk retains its contents without power, storing data as magnetic patterns on rotating platters, so it is non-volatile. Solid-state drives, flash memory, optical discs and ROM are non-volatile for the same reason. The other three are all volatile and lose their contents the moment power is removed. Registers sit inside the processor and are the fastest storage of all, holding the operands of the current instruction. SRAM cache comes next, built from flip-flops and needing no refresh. DRAM main memory stores each bit as charge on a capacitor that leaks, so it must be refreshed thousands of times a second - which is exactly why it is volatile. These form the memory hierarchy: as one moves outward from registers to cache to main memory to disk, capacity rises and cost per bit falls, while speed falls by orders of magnitude at each step. Volatility changes at the last step.

51.

A JK flip-flop toggles its output when both J and K inputs are HIGH.

A.True
B.False

Answer: B

Correct answer: True

The statement is true, and it is the feature that makes the JK flip-flop the most versatile of the four types. Its behaviour on a clock edge is: J = 0, K = 0 holds the previous state; J = 0, K = 1 resets to 0; J = 1, K = 0 sets to 1; and J = 1, K = 1 toggles, so the output becomes the complement of what it was. The toggle case is precisely what the SR flip-flop cannot do. In an SR flip-flop, setting both inputs high is a forbidden condition, because it drives both outputs to the same level and leaves the next state indeterminate when the inputs are released. The JK resolves that by feeding the outputs back into the input gating, turning the invalid case into a useful one. Tying J and K together to a permanent 1 gives a T flip-flop, which toggles on every clock pulse - and that is the building block of binary counters, since each stage divides the frequency by two.

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52.

Minimum number of bits required to represent B is

Answer: C

Correct answer: 3

Three bits distinguish eight values, which is the smallest power of two large enough for the symbol set in question: \( 2^{2}=4 \) is too few and \( 2^{3}=8 \) suffices.

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53.

A latch is level-triggered while a flip-flop is edge-triggered.

A.True
B.False

Answer: A

Correct answer: True

A latch responds to its inputs for as long as the enable line is active, whereas a flip-flop samples only at the rising or falling edge of the clock. Edge triggering is what keeps a synchronous circuit’s stages from racing ahead of each other.

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54.

What can happen at a Token Ring station

A.Examination of the destination address
B.Regeneration of the frame
C.Passing of the frame to the next station
D.All of these

Answer: D

Correct answer: All of these

Every station on a Token Ring acts as a repeater: it examines the destination address to see whether the frame is for it, regenerates the signal, and passes the frame on round the ring.

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55.

Which number system is used internally by digital computers?

A.Binary
B.Decimal
C.Octal
D.Hexadecimal

Answer: D

Correct answer: Binary

Digital computers work internally in binary, base 2, using only the digits 0 and 1. The reason is physical rather than mathematical. A circuit can distinguish two voltage levels reliably and cheaply - on or off, high or low - and that reliability degrades quickly if more levels must be told apart. Two states also map directly onto the switching behaviour of a transistor and onto the true and false of Boolean algebra, which is what makes logic gates possible. Octal and hexadecimal are used by people rather than by machines, as compact ways of writing binary: each octal digit stands for exactly three bits and each hexadecimal digit for exactly four, so conversion is done by grouping rather than by division. A byte such as 11010110 becomes D6 in hexadecimal at a glance. Decimal is what humans use, and converting between it and binary requires actual arithmetic, which is why it is not used internally.

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56.

The number of distinct states in a 3-bit binary counter is

Answer: C

Correct answer: 8

A counter with \( n \) bits passes through \( 2^{n} \) distinct states, so with three bits \[ 2^{3} = 8, \] running from 000 to 111 - decimal 0 to 7 - before returning to 000. That return is why such a device is called a modulus-8 counter, and why its highest output is the clock frequency divided by eight. Counters are therefore used as frequency dividers as often as they are used to count. The same relation works in reverse: a counter of modulus \( N \) needs the smallest \( n \) for which \( 2^{n} \ge N \). A decade counter of modulus 10 needs four flip-flops, and the six surplus states are removed by feedback that clears the counter when it reaches ten. It is the identical arithmetic that fixes the number of select lines on a multiplexer, the outputs of a decoder and the address lines of a memory - one relation worth being fluent in.

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57.

In an AND gate, the output is HIGH only when all inputs are HIGH.

A.True
B.False

Answer: A

Correct answer: True

The statement is true. An AND gate outputs 1 only when every one of its inputs is 1; if any input is 0 the output is 0. Its Boolean expression is \( Y = A \cdot B \). Its truth table for two inputs runs: 0,0 gives 0; 0,1 gives 0; 1,0 gives 0; 1,1 gives 1. Only the last row gives 1. A useful way to remember it is that AND behaves exactly like ordinary multiplication on the digits 0 and 1, which is why the operation is written with a dot and often called the logical product. OR is correspondingly called the logical sum, though \( 1 + 1 = 1 \) breaks the analogy there. The AND gate is also used as an enable: holding one input at 1 lets the other pass through unchanged, and holding it at 0 blocks the signal. That is how a clock is gated on and off in practice.

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58.

Non-polling system is

A.TDMA
B.stop and wait
C.continuous ARQ
D.none of these

Answer: A

Correct answer: TDMA

In TDMA each station has its own time slot and transmits in it without being asked, so no station has to be polled. Stop-and-wait and continuous ARQ are error-control schemes rather than access methods.

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59.

What is the main function of a shift register ?

A.To add binary numbers
B.To move stored bits one position per clock pulse
C.To decode binary inputs
D.To generate clock pulses

Answer: B

Correct answer: To move stored bits one position per clock pulse

A shift register is a chain of flip-flops in which each clock pulse passes the stored bit along to the next stage. This makes it the standard means of converting between serial and parallel data.

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60.

Which of these is an example of non-volatile storage?

A.Hard disk
B.SRAM cache
C.DRAM main memory
D.CPU register

Answer: C

Correct answer: Hard disk

A hard disk retains its contents without power, storing data as magnetic patterns on rotating platters, so it is non-volatile. Solid-state drives, flash memory, optical discs and ROM are non-volatile for the same reason. The other three are all volatile and lose their contents the moment power is removed. Registers sit inside the processor and are the fastest storage of all, holding the operands of the current instruction. SRAM cache comes next, built from flip-flops and needing no refresh. DRAM main memory stores each bit as charge on a capacitor that leaks, so it must be refreshed thousands of times a second - which is exactly why it is volatile. These form the memory hierarchy: as one moves outward from registers to cache to main memory to disk, capacity rises and cost per bit falls, while speed falls by orders of magnitude at each step. Volatility changes at the last step.

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