Computer Network Questions and Answers

Answer: C

Correct answer: 11010

Dividing repeatedly by two and reading the remainders upward gives the answer. 26 gives remainder 0, then 13 gives 1, then 6 gives 0, then 3 gives 1, then 1 gives 1 - reading upward, 11010. The check is quicker than the derivation: the place values from the left are 16, 8, 4, 2, 1, so 11010 is \[ 16 + 8 + 0 + 2 + 0 = 26. \] An alternative method subtracts the largest power of two that fits and repeats: 26 − 16 = 10, 10 − 8 = 2, 2 − 2 = 0, so the bits at 16, 8 and 2 are set. The distractors are all near misses of the kind produced by reversing the remainder order or dropping a bit, which is why reading the remainders in the right direction matters. In hexadecimal 26 is 1A, and grouping 11010 into fours from the right - 0001 1010 - gives 1 and A directly.

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: A

Correct answer: is faster than main memory and holds recently used data

Cache is a small, very fast memory placed between the processor and main memory, holding copies of data and instructions that have recently been used or are likely to be used next. It works because of the principle of locality. Temporal locality means a location just accessed is likely to be accessed again soon; spatial locality means nearby locations are likely to be accessed next, which is why data is fetched in whole cache lines rather than single bytes. A request found in cache is a hit and is served in a few processor cycles; a miss requires main memory and costs hundreds. Because hit rates in practice exceed 90 per cent, the average access time approaches that of the cache. It is built from SRAM, which uses a flip-flop per bit and needs no refreshing, unlike the DRAM of main memory - faster but far more expensive per bit, which is why cache is small. Modern processors use several levels, L1 through L3.

Answer: D

Correct answer: all four inputs

AND requires every input to be HIGH; a single LOW input forces the output LOW however many other inputs are HIGH.

Answer: C

Correct answer: Distributive law

This is the distributive law, which lets AND be distributed over OR just as multiplication distributes over addition in ordinary algebra. Boolean algebra also allows the reverse form, A + BC = (A + B)(A + C), which has no arithmetic counterpart.

Answer: B

Correct answer: (A · B)’ = A’ + B’

De Morgan’s second theorem states that the complement of a product equals the sum of the complements: (A · B)’ = A’ + B’. In gate terms, a NAND is the same as an OR gate fed by inverted inputs.

Answer: B

Correct answer: RAM

RAM is volatile: it loses its contents the moment power is removed. It is used as working memory precisely because it is fast and freely writable, and its impermanence is the price of that. The other three are non-volatile and retain data without power. ROM is written once at manufacture; EPROM can be erased by ultraviolet light and reprogrammed; flash memory is electrically erasable and is what solid-state drives and memory cards are built from. RAM itself divides in two. SRAM stores each bit in a flip-flop, needs no refreshing, and is fast but expensive, so it is used for cache. DRAM stores each bit as a charge on a tiny capacitor, which leaks and must be refreshed thousands of times a second, but it is far denser and cheaper, so it is used for main memory. The name random access distinguishes both from sequential media such as tape, where access time depends on position.

Answer: B

Correct answer: The output toggles

With J = K = 1 the JK flip-flop toggles, changing state on every clock edge. This is the case the SR flip-flop leaves undefined, and removing that forbidden state is the reason the JK design exists.

Answer: A

Correct answer: NAND

NAND is a universal gate, meaning that any logic function whatever can be built using NAND gates alone. NOR is the other universal gate. The proof is constructive. An inverter is a NAND with both inputs tied together. An AND is a NAND followed by that inverter. An OR is a NAND fed by two inverters, which is De Morgan’s theorem realised in hardware: \( \overline{\bar{A} \cdot \bar{B}} = A + B \). Since AND, OR and NOT together are sufficient for every Boolean function, and all three can be made from NAND, NAND alone is sufficient. The property matters commercially. A manufacturer can fabricate a whole logic family from one repeated cell, which simplifies design, testing and inventory, and the regularity suits automated layout. AND, OR and XOR are not universal, because none of them can produce an inversion: with only non-inverting gates, an input of all 1s can never yield a 0.

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.