Computer Network Questions and Answers

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.

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.

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.

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.

Answer: C

Correct answer: 255

With \( n \) bits there are \( 2^{n} \) distinct patterns, so eight bits give 256 of them - but they represent the values 0 to 255, since one pattern is used for zero. Hence the maximum is \[ 2^{8} - 1 = 255. \] The off-by-one is the whole point of the question, and 256 is the classic wrong answer: it is the count of values, not the largest of them. That is unsigned. If the eight bits hold a signed value in 2’s complement, the range becomes −128 to +127 - which is where the other two distractors come from. The asymmetry arises because 2’s complement has a single representation of zero, leaving one more pattern for the negatives than for the positives. The pattern 11111111 is therefore 255 when read as unsigned and −1 when read as signed. Nothing in the bits themselves says which is meant; it is the instruction operating on them that decides.

Answer: C

Correct answer: 3

An encoder performs the reverse of a decoder, turning one active input among \(2^n\) into an \(n\)-bit code. With 8 inputs, \(2^3 = 8\) gives three output lines.

Answer: C

Correct answer: stores one bit of information

A flip-flop is a bistable circuit: it has two stable states and remains in whichever it was last put into, so it stores exactly one bit. It is the basic element of all sequential logic and of static memory. The distinction from combinational logic is the essential one. A combinational circuit’s output depends only on its present inputs; a sequential circuit’s output depends on its inputs and on its stored state, which is what gives it memory. The common types are the SR flip-flop, which sets and resets but has a forbidden input combination; the D flip-flop, which simply captures the value on its data input at the clock edge; the JK, which resolves the SR ambiguity by toggling; and the T, which toggles on each clock pulse. Chained together, flip-flops make registers, shift registers and counters. A latch is the level-triggered relative of the edge-triggered flip-flop.

Answer: B

Correct answer: interface card

Every machine on a LAN needs a network interface card to put frames on the cable and take them off. A modem is for telephone lines, which is a wide-area connection.

Answer: C

Correct answer: both (a) and (b)

Slotted ALOHA divides time into slots equal to one frame time and allows transmission only at a slot boundary, which halves the vulnerable period and doubles the throughput. Both properties follow from the same requirement: every station must agree on where the slots begin, which needs global synchronisation.

Answer: D

Correct answer: All of these

A wide area network spans distances no single medium covers economically, so it uses whatever is available: leased telephone lines, terrestrial microwave links and satellite hops.