Question 1

Computer architecture basics — which item is NOT a core functional block? Select the option that does not belong to the standard functional blocks of a general-purpose computer system.

Accepted Answer

Introduction / Context: Most introductory computer architecture models describe a few core functional blocks present in virtually all systems. Recognizing which components are fundamental and which are optional peripherals helps students understand minimal system requirements vs. application-specific extensions. Given Data / Assumptions: Core blocks typically include CPU, memory, and I/O interfaces. Peripherals such as converters, sensors, and actuators are application-dependent. Concept / Approach: A general-purpose computer requires a processing unit to execute instructions, memory to store code/data, and I/O ports to communicate with the outside world. An analog-to-digital converter (ADC) is crucial in embedded and instrumentation systems but is not universally required in computers (e.g., servers and laptops often lack dedicated ADC hardware). Therefore, it is not part of the minimal canonical block diagram. Step-by-Step Solution: List canonical blocks → CPU, memory, I/O.Identify optional peripherals → ADCs, DACs, sensors.Select the non-core item → Analog-to-digital converter. Verification / Alternative check: Standard textbooks depict the von Neumann or Harvard model showing CPU, memory, and I/O as the primary blocks; ADCs appear only in embedded system examples when analog signals are present. Why Other Options Are Wrong: CPU, memory, and I/O ports are essential to execute programs and communicate with devices. System interconnect (bus/NoC) is part of how these blocks communicate; while architectural, it is inherent to the system. Common Pitfalls: Assuming all modern systems need ADCs; many purely digital systems do not interface with analog signals at all. Final Answer: Analog-to-digital converter

Question 2

Address space calculation — locations addressed by a 20-bit bus Given an address bus width of 20 bits in a microprocessor system, how many unique memory locations can be addressed?

Accepted Answer

Introduction / Context: Address bus width directly determines the size of the addressable memory space in byte-addressable architectures. Computing the total number of locations is a foundational skill in digital systems and computer architecture courses. Given Data / Assumptions: Address bus has 20 lines (bits). Each unique combination selects one memory location (typically one byte). We assume simple linear addressing without bank switching. Concept / Approach: With N address lines, the number of distinct addresses equals 2^N. For N = 20, the total is 2^20. This is a power-of-two calculation commonly encountered when sizing ROM/RAM devices and when interpreting legacy architectures such as the 8086 with a 20-bit physical address bus (1 MB space). Step-by-Step Solution: Compute total addresses: 2^N with N = 20.2^10 = 1,024; therefore 2^20 = (2^10)^2 = 1,024 * 1,024.1,024 * 1,024 = 1,048,576.Hence, 1,048,576 unique locations are addressable. Verification / Alternative check: Cross-check by noting that 2^20 bytes equals 1 MB (using the binary definition: 1 MB = 1,048,576 bytes), which aligns with many classic systems. Why Other Options Are Wrong: 2,097,152 (2^21), 4,194,304 (2^22), 8,388,608 (2^23) are for larger buses. 524,288 corresponds to 2^19, which is too small. Common Pitfalls: Confusing decimal megabytes (1,000,000) with binary megabytes (1,048,576). Final Answer: 1,048,576 locations

Question 3

Polled I/O — when is it the preferred strategy? Select the condition under which a polling-based input/output scheme is generally most appropriate compared to interrupts or DMA.

Accepted Answer

Introduction / Context: Polled I/O is a simple technique where the CPU periodically checks device status flags and services devices when they are ready. While easy to implement, it can be inefficient or unfair if multiple devices require urgent attention. Understanding when polling is acceptable helps balance simplicity and responsiveness. Given Data / Assumptions: System has one or more peripherals with status registers. No strict real-time deadlines that demand immediate CPU attention. CPU time is available for routine checks without starving tasks. Concept / Approach: Polling works best when devices have similar service needs and there is no strict priority ordering. If priority matters (e.g., emergency sensors), interrupt-driven or DMA-based solutions are better because they allow devices to signal the CPU asynchronously and with a defined priority, minimizing latency for critical events. Step-by-Step Solution: List system constraints → low urgency, predictable workloads.Select I/O method → polling is sufficient when no device must preempt others.Confirm → absence of priority considerations favors polling. Verification / Alternative check: Design guidelines in embedded systems texts recommend polling for simple, slow, or evenly weighted tasks, switching to interrupts for sporadic or high-priority events. Why Other Options Are Wrong: Frequent priority needs or random preemption require interrupts, not polling. Options about “polling rate above/below 1000 s” are arbitrary thresholds and not a general rule. Common Pitfalls: Trying to scale polling to many time-critical devices; latency and jitter quickly become unacceptable. Final Answer: there are no priority considerations

Question 4

Which x86 microprocessor family used multiplexed address/data lines on its external bus? Choose the processor that famously time-shared AD lines (address during T1, data during later bus states) to reduce pin count.

Accepted Answer

Introduction / Context: To minimize package pins, early microprocessors often multiplexed address and data on the same physical lines and used a signal such as ALE to latch the address externally. Recognizing which generation used this technique helps when reading legacy schematics and timing diagrams. Given Data / Assumptions: Multiplexed lines labeled AD0–AD15 on 8086/8088. ALE (Address Latch Enable) demultiplexes the address into external latches. Concept / Approach: The 8086/8088 bus cycles place address on the AD lines during the first state (T1) and data on those same lines during subsequent states (T2–T4). Later processors increased pin counts and bus widths, reducing the need for such multiplexing at the package level in typical implementations. Step-by-Step Solution: Identify the architecture with ADx lines → 8086/8088.Recall use of ALE and external latches (e.g., 74HC373) to capture addresses.Conclude → 8086/8088 is the correct choice. Verification / Alternative check: Original Intel hardware manuals show bus timing with multiplexed address/data phases and ALE strobes. Why Other Options Are Wrong: 80286/80386/Pentium/Core: later designs typically expose separate address and data buses or very different bus protocols. Common Pitfalls: Assuming all x86 generations share identical external bus wiring; many details changed substantially across generations. Final Answer: 8086/8088

Question 5

Definition of mnemonic in assembly programming: A mnemonic is an English-like assembly instruction that an assembler converts into the corresponding machine code for the processor.

Accepted Answer

Introduction / Context: Programmers rarely write raw opcodes. Instead, they use mnemonics—short words that represent instructions—to make low-level coding practical. Understanding the role of mnemonics clarifies the distinction between assembly, machine code, and higher-level languages. Given Data / Assumptions: An assembler is available to translate mnemonics into binary opcodes. Target CPU executes the binary according to its instruction set. A mnemonic is part of the executable statement, not merely a comment. Concept / Approach: Each mnemonic corresponds to a specific instruction encoding. Assemblers also support labels, constants, and directives to control layout, but the core function is mapping mnemonic + operands into machine language. This lets developers reason about program behavior while leaving bit-level encoding to the toolchain. Step-by-Step Solution: Write mnemonic-level source (e.g., MOV, ADD, JMP).Assembler parses and encodes to machine instructions.Link/locate and load the resulting binary to run on hardware. Verification / Alternative check: Disassemblers reverse the process, showing mnemonics from binary images. Comparing assembler listing files verifies one-to-one mapping for each instruction line. Why Other Options Are Wrong: Incorrect: Opposite of assembly’s purpose. “Only comments”: Mnemonics are executable instructions; comments are ignored by the assembler. “Compiled to C first”: Assemblers emit machine code directly. “BIOS function name”: Those are software interfaces, not instruction mnemonics. Common Pitfalls: Confusing directives (e.g., .org) with instructions; assuming identical mnemonics across architectures; forgetting that addressing modes affect encoding length even for the same mnemonic family. Final Answer: Correct

Question 6

Machine language and processor dependence: Is machine language independent of the type of microprocessor used in a computer system?

Accepted Answer

Introduction / Context: Machine language is the lowest-level software representation of instructions a specific CPU can execute. Different microprocessors implement different instruction sets, encodings, and execution semantics. This question probes whether you correctly identify machine code as CPU-specific rather than universal. Given Data / Assumptions: Each CPU family (e.g., 8085, 8051, AVR, ARM) defines its own instruction set and opcode encodings. Binary images are interpreted according to the target CPU’s ISA. No compatibility layer (such as a software emulator) is assumed. Concept / Approach: Because opcodes are simply patterns of bits, they only gain meaning relative to a CPU’s decoder. An opcode that means “ADD” on one architecture could be invalid or mean something else on another. Therefore, machine language is inherently processor dependent. Portability requires recompilation/assembly for the target ISA or an emulator that translates foreign opcodes. Step-by-Step Solution: Identify the target architecture (ISA) for the binary.Assemble/compile code specifically for that ISA.Run the resulting machine code on compatible hardware only. Verification / Alternative check: Try to execute an 8085 binary on an 8051: the CPU will not interpret the opcodes correctly. Cross-assemblers generate different binaries for different targets from the same source, confirming dependence on ISA. Why Other Options Are Wrong: “Independent” claims contradict the definition of ISA. “Independent only for arithmetic” is incorrect; all encodings are ISA-specific. “Independent if you use an emulator” shifts execution to the emulator; the underlying dependency remains. “Independent for 8-bit only” is false; bit width does not change ISA dependence. Common Pitfalls: Assuming source code portability implies binary portability; ignoring endianness, calling conventions, and instruction encodings when moving binaries between architectures. Final Answer: Dependent: machine code is specific to the microprocessor ISA

Question 7

Processor design goals: Are chip designers always focused primarily on increasing clock frequency, regardless of other considerations such as power, parallelism, or IPC?

Accepted Answer

Introduction / Context: Clock speed (MHz/GHz) is only one factor in processor performance. Architects balance frequency with instructions per cycle (IPC), core count, cache hierarchy, memory bandwidth, specialized accelerators, and power/thermal constraints. This question tests conceptual understanding that “more GHz” is not the sole or always the primary design goal. Given Data / Assumptions: Modern chips face power density and thermal limits. Workloads benefit from wider superscalar pipelines, out-of-order execution, vector units, and multiple cores. Energy efficiency (performance per watt) is often a dominant metric. Concept / Approach: After the breakdown of Dennard scaling, raising frequency dramatically increases power (roughly proportional to V^2 * f). Designers therefore pursue IPC improvements, parallelism (multi-core, GPU, DSP, NPU), and domain-specific accelerators. For many applications, total throughput and energy efficiency outweigh raw clock speed. Step-by-Step Solution: Recognize that frequency increases power and heat, limiting gains.Improve IPC via microarchitectural enhancements (branch prediction, caching, wider issue).Scale performance with multicore and heterogeneous compute units. Verification / Alternative check: Compare processors across generations: some newer chips run at similar frequencies but deliver higher performance through IPC, more cores, and larger caches, demonstrating that GHz alone is not the strategy. Why Other Options Are Wrong: “Higher GHz is always the sole objective” ignores practical power/thermal constraints. Mobile/server-only statements are incorrect; the trade-offs apply across domains. Historical claims (e.g., “only before 2000”) are oversimplified. Common Pitfalls: Equating clock speed with user-experienced performance; overlooking workload characteristics and bottlenecks like memory latency; ignoring the efficiency benefits of accelerators and vectorization. Final Answer: Incorrect: performance also comes from IPC, parallelism, and efficiency

Question 8

Definition of polling in I/O handling: Polling means the CPU repeatedly checks device status within the normal instruction flow, not that it pauses execution to run a separate I/O routine automatically.

Accepted Answer

Introduction / Context: Polling and interrupts are two fundamental I/O servicing methods. Polling is software-driven status checking performed by the CPU at regular intervals or in loops. Interrupts are hardware-driven events that suspend the current instruction stream to service an interrupt handler. This question distinguishes these mechanisms. Given Data / Assumptions: Polling involves reading device status registers to decide when to transfer data. Interrupts cause an automatic context switch to a service routine. DMA is independent of polling vs. interrupts. Concept / Approach: In polling, the CPU executes normal code that includes checks like “is transmit buffer empty?” or “has data arrived?” If the condition is met, it performs I/O; otherwise, it continues or waits in a controlled loop. There is no automatic diversion by hardware. In interrupts, hardware signals the CPU to pause the current flow and jump to an ISR, then return after servicing. Step-by-Step Solution: Implement a loop that reads a status bit.If set, read/write the data register; if not, continue or check again later.Contrast with interrupts, where the CPU branches to an ISR without explicit polling code at that moment. Verification / Alternative check: Trace program counters: in polling, execution follows the main path; in interrupts, the PC saves the current location and jumps to the ISR upon an interrupt request. Why Other Options Are Wrong: “Pauses to execute an interrupt routine” describes interrupts, not polling. “Correct only with DMA/RTOS/serial” imposes irrelevant constraints; polling is general. Common Pitfalls: Confusing busy-wait polling with blocking delays; assuming polling cannot meet real-time needs (it can, if loop timing is bounded); overlooking CPU usage overhead of continuous polling vs. interrupt efficiency. Final Answer: Correct: polling is active status checking in the main program flow

Question 9

x86 family compatibility claim: For the 80x86 (x86) family, are instructions downward/backward compatible such that code written for earlier processors runs on later processors?

Accepted Answer

Introduction / Context: The x86 family is renowned for backward compatibility. Over decades, new processors have added instructions and modes while retaining the ability to execute legacy binaries targeting earlier members. This question checks recognition of that design philosophy. Given Data / Assumptions: Later x86 processors include earlier instruction sets plus extensions. Operating modes (real, protected, long) exist, but CPUs can enter modes that support legacy execution. Some features require OS support, yet basic compatibility for older binaries is preserved. Concept / Approach: Backward (often colloquially called downward) compatibility means that code produced for an older CPU runs unmodified on newer hardware. The ISA grows by extension rather than replacement. Therefore, an 8086 or 80286 binary can run on a modern x86 processor when the environment permits appropriate mode/emulation (e.g., real/protected mode or virtualization). Step-by-Step Solution: Identify that new x86 generations are supersets of the earlier ISA.Establish that newer chips can execute the older instruction encodings.Conclude that the family is backward compatible for legacy binaries. Verification / Alternative check: Historical software and OS bootloaders from early PCs can run on later machines under proper mode settings or emulation, demonstrating the preserved binary semantics. Why Other Options Are Wrong: “Breaks binary compatibility” contradicts x86’s continuity. “Only real-mode” or “only arithmetic” artificially restricts compatibility. “Requires source recompilation” is unnecessary for true backward compatibility. Common Pitfalls: Confusing OS/environment limitations with CPU ISA compatibility; assuming that 64-bit-only environments without 32-bit support reflect CPU limits rather than OS configuration. Final Answer: Yes: later x86 CPUs run code for earlier family members

Question 10

What is a coprocessor? A coprocessor is a specialized microprocessor with a limited, domain-focused instruction set optimized to perform arithmetic or numeric operations at very high speed alongside the main CPU.

Accepted Answer

Introduction / Context: Coprocessors augment a general-purpose CPU by accelerating specific classes of operations. Classic examples include floating-point units (FPUs) like the Intel 8087, graphics processors (GPUs), and digital signal processors (DSPs) used as auxiliaries. They offload computationally intensive tasks, increasing system throughput and freeing the CPU for control logic and general tasks. Given Data / Assumptions: A coprocessor focuses on a subset of operations (e.g., floating point, vector math, signal processing). Instruction set is specialized/limited relative to a full CPU. Works in tandem with the main processor via instruction prefixes, command queues, or shared memory/microcode interfaces. Concept / Approach: Specialization enables tailored hardware pipelines, wider datapaths, and optimized execution units for a particular numeric domain. This yields higher performance and efficiency than implementing the same operations solely in a general-purpose scalar pipeline. The main CPU orchestrates tasks and delegates heavy computation to the coprocessor when appropriate. Step-by-Step Solution: Identify numeric workload hotspots (e.g., matrix math, FFT).Map them to coprocessor instructions or kernels (FPU ops, SIMD vectors, DSP MACs).Integrate results back into the CPU-controlled program flow. Verification / Alternative check: Benchmarks show dramatic speedups for floating-point and vector workloads when using FPUs/SIMD versus software emulation on integer-only cores, validating the definition and purpose of a coprocessor. Why Other Options Are Wrong: Incorrect: Denies the widely accepted definition. “Only a DMA controller” or “cache controller” describe other subsystems, not coprocessors. “Replaces the CPU entirely” is incorrect; a coprocessor complements, not replaces, the CPU. Common Pitfalls: Assuming coprocessors are limited to legacy FPUs; overlooking modern forms like GPUs and AI accelerators; confusing bus-mastering peripherals (e.g., DMA) with instruction-executing coprocessors. Final Answer: Correct

Question 11

Computer architecture history and caches: Was the original Intel Pentium (P5) the first central processing unit to introduce separate instruction and data L1 caches (split I-cache and D-cache)? Choose the most accurate evaluation.

Accepted Answer

Introduction / Context: Cache organization is a foundational topic in computer architecture. Many learners associate the Intel Pentium with modern features such as superscalar pipelines and split L1 caches. This question asks whether the original Pentium was the first CPU to provide separate instruction and data caches, and it requires historical context across multiple architectures, not just Intel x86. Given Data / Assumptions: “Original Pentium” refers to Intel’s P5 microarchitecture introduced in the early 1990s. “Separate caches” means distinct L1 instruction (I-cache) and data (D-cache) storage (a Harvard-like split at L1). We compare across CPUs generally, not only within the x86 family. Concept / Approach: We evaluate whether the Pentium was the first to introduce split L1 caches in the industry. The method is to recall earlier processors and check if any implemented separate I/D caches before Pentium’s launch. If earlier examples exist, the statement is incorrect. Step-by-Step Solution: Identify Pentium’s L1 configuration: 8 KB I-cache and 8 KB D-cache, both on-die and separate.Survey earlier non-x86 CPUs: several RISC CPUs (for example, MIPS and SPARC designs) and Motorola 68040 used split L1 caches prior to the Pentium timeframe.Conclude that while Pentium popularized split caches in mainstream x86 PCs, it was not the first CPU overall to feature this organization.Therefore, the most accurate evaluation of the statement is “Incorrect.” Verification / Alternative check: Architecture references for Motorola 68040 and various early RISC processors document separate instruction and data caches predating the Pentium. Intel’s own 80486 used a unified L1 cache, highlighting Pentium’s shift, but the broader industry had split caches earlier. Why Other Options Are Wrong: Correct: Wrong because earlier processors already had split caches.Depends on chipset version only: Cache organization is part of the CPU core design, not merely the chipset.Cannot be determined from the given data: Historical evidence is well known; it can be determined. Common Pitfalls: Assuming Intel x86 history equals overall CPU history; conflating being “first in x86” with “first in the industry.” Final Answer: Incorrect

Question 12

Pentium superscalar capability: Evaluate the statement: “The Intel Pentium processor can dispatch and execute two instructions simultaneously under suitable conditions.”

Accepted Answer

Introduction / Context: The early to mid-1990s introduced superscalar execution to mainstream desktop CPUs. The Pentium (P5) microarchitecture is notable for its dual integer pipelines (U and V), enabling limited dual-issue under certain pairing rules. This question tests understanding of that capability. Given Data / Assumptions: Pentium has two integer pipelines named U and V. Dual-issue occurs only when instructions are pairable and data/structural hazards are absent. Floating-point and certain complex instructions may serialize or restrict pairing. Concept / Approach: To validate the claim, recall that superscalar designs can fetch, decode, and (sometimes) execute more than one instruction per cycle. The Pentium is a dual-pipeline design that can, in favorable cases, retire two integer instructions per cycle. Step-by-Step Solution: Identify the architectural feature: dual pipelines (U/V).Apply pairing rules: simple integer ops can pair; dependencies or specific instruction types may prevent pairing.Conclude: The architecture can execute two instructions at once when constraints are met.Therefore, the statement is “Correct.” Verification / Alternative check: Vendor documentation and optimization manuals describe pairing rules, scheduling, and pipeline hazards, all consistent with dual-issue capability. Why Other Options Are Wrong: Incorrect: Contradicts well-documented dual-pipeline design.Only in protected mode: Execution width is architectural, not strictly a CPU mode property.Cannot be determined without cache details: Caches affect performance, not the fundamental dual-issue capability. Common Pitfalls: Assuming two-at-once always happens; ignoring dependencies and pairing restrictions; confusing decode bandwidth with execution. Final Answer: Correct

Question 13

PowerPC execution width claim: Assess the statement: “A PowerPC processor can effectively execute up to ten instructions per clock cycle.” Choose the best evaluation.

Accepted Answer

Introduction / Context: Superscalar width indicates how many instructions a processor can issue/execute per cycle under ideal conditions. Typical desktop-class PowerPC microarchitectures (e.g., 603/604/G3/G4/G5 families) provided decode/issue widths far below ten. This question checks realism regarding execution width claims. Given Data / Assumptions: Common PowerPC cores are 2- to 4-wide issue in many generations. Back-end execution units (integer, floating, load/store, branch) allow parallelism but not “ten per cycle.” Marketing peak counts sometimes blend micro-ops or vector lanes, but not as ten separate scalar instructions each cycle. Concept / Approach: We compare the ten-per-cycle claim to documented decoder/issue widths and practical sustained IPC. Even with aggressive out-of-order execution and multiple units, reaching ten scalar instructions per cycle is not credible for these designs. Step-by-Step Solution: Review typical PowerPC decode/issue widths: commonly 2–4.Consider peak IPC metrics: actual sustained IPC much lower due to dependencies and cache effects.Conclude the ten-per-cycle claim is unrealistic for these cores.Thus the best evaluation is “Incorrect.” Verification / Alternative check: Microarchitecture references and benchmarking show IPC values well below ten; instruction issue width specifications corroborate this. Why Other Options Are Wrong: Correct: Not supported by core specs.Only true with simultaneous multithreading: Even SMT does not yield ten scalar instructions per cycle on these designs.Indeterminate without compiler details: Compilers affect IPC, but hardware width imposes hard ceilings. Common Pitfalls: Confusing vector element throughput with instruction count; conflating theoretical back-end ports with front-end decode width. Final Answer: Incorrect

Question 14

System buses classification: Evaluate the statement: “The PCI bus is an external bus for personal computers.” Decide whether this characterization is accurate.

Accepted Answer

Introduction / Context: Computer buses are often categorized as internal (on the motherboard/backplane) versus external (user-accessible peripheral interconnects like USB or Thunderbolt). The Peripheral Component Interconnect (PCI) standard revolutionized internal expansion during the 1990s. This question asks whether PCI is an “external” bus. Given Data / Assumptions: PCI is a motherboard expansion bus for add-in cards. External buses typically refer to self-powered ports or cables exposed outside the chassis. PCI slots are inside the PC case, not externally accessible during normal use. Concept / Approach: Classify PCI according to location and usage. Internal buses connect components on the board or backplane; external buses connect devices via cables outside the chassis. PCI is therefore internal, even though it connects to peripherals via add-in cards. Step-by-Step Solution: Identify PCI as a local expansion interconnect on the motherboard.Contrast with external buses (e.g., USB, IEEE-1394) that route outside the chassis.Conclude the statement claiming PCI is external is inaccurate.Select “Incorrect.” Verification / Alternative check: Motherboard manuals and standards documents place PCI firmly as an internal bus; external connectivity may be provided by cards that use PCI internally. Why Other Options Are Wrong: Correct: Misclassifies PCI.Only correct for laptops / True for PCI Express only: Both PCI and PCIe are internal interconnects; Mini-PCIe slots in laptops are still internal. Common Pitfalls: Equating “external devices” with “external bus”; confusing expansion capability with physical externality. Final Answer: Incorrect

Question 15

Assembly and high-level programming terminology: Contiguous sequences of bytes or words processed as a unit (with instructions like MOVS, CMPS, SCAS on x86) are commonly called ________.

Accepted Answer

Introduction / Context: Processors and programming languages provide mechanisms to operate on contiguous blocks of memory. In x86 assembly, a dedicated set of instructions handles such operations efficiently. This question targets the common term used to describe those contiguous sequences. Given Data / Assumptions: Operations may include moving, comparing, scanning, or storing bytes/words/dwords sequentially. x86 provides instructions such as MOVS, CMPS, SCAS, STOS, and LODS. High-level code often maps to library “string/memory” functions. Concept / Approach: The umbrella term for contiguous sequences of characters or arbitrary bytes in many contexts is “strings.” While “string” often implies character data, at the instruction-set level it broadly denotes contiguous memory elements processed repetitively. Step-by-Step Solution: Identify that the target is a contiguous sequence in memory.Recall x86 “string instructions” that operate with REP prefixes for repeated processing.Match the term used historically in documentation: “strings.”Select “strings.” Verification / Alternative check: Intel and AMD manuals call these “string operations,” covering byte/word/dword sequences independent of textual meaning. Why Other Options Are Wrong: data transfer: A general instruction class; not specifically contiguous sequences.arithmetic: Numeric operations, not sequence handling.loops and jumps: Control-flow constructs, not data sequences. Common Pitfalls: Assuming “strings” only mean ASCII text; overlooking that string ops also manipulate arbitrary memory blocks. Final Answer: strings

Question 16

Microcomputer buses and directionality: Identify which bus in a typical microcomputer system is inherently unidirectional.

Accepted Answer

Introduction / Context: Digital systems use several buses to interconnect the CPU, memory, and peripherals. Understanding directionality helps with timing analysis, tri-state design, and bus arbitration. This item focuses on which bus is unidirectional by design. Given Data / Assumptions: Address bus carries memory or I/O addresses from master (often the CPU) to slaves. Data bus transfers read or write data, typically bidirectional. Control bus carries various signals (read/write, clock, interrupt lines), some driven by CPU, others by peripherals. Concept / Approach: The address bus identifies the target location and flows outward from the address source to all addressed devices. Data movement, however, goes in either direction depending on read or write cycles, and control lines vary by role. Step-by-Step Solution: Consider address phase: CPU (or bus master) asserts an address; devices listen.Recognize data phase: during reads, data flows from memory/peripheral to CPU; during writes, from CPU to device (bidirectional overall).Control bus lines are mixed, not purely unidirectional overall.Thus, the unidirectional bus is the address bus. Verification / Alternative check: Textbook bus diagrams consistently show address lines as outputs from the processor toward the system; data lines are shown with bidirectional arrows. Why Other Options Are Wrong: data bus: Clearly bidirectional in read/write cycles.control bus: A collection of signals with mixed directions; not a single unidirectional path.all of the above: Incorrect because only the address bus is unidirectional. Common Pitfalls: Assuming tri-state implies bidirectionality for all buses; conflating bus masters with signal direction. Final Answer: address bus

Question 17

Instruction classification: MOV, PUSH, and POP belong to which instruction category in a typical CPU instruction set?

Accepted Answer

Introduction / Context: Instruction sets are grouped into categories such as data transfer, arithmetic/logic, control flow, and bit manipulation. Recognizing categories improves readability and helps optimize compilers and hand-written assembly. Given Data / Assumptions: MOV copies data between registers/memory. PUSH places data on the stack; POP retrieves it. None of these perform arithmetic; they move or stage data. Concept / Approach: All three instructions move data from one place to another or change storage location (registers/stack), fitting the “data transfer” category. Step-by-Step Solution: Identify effects: MOV copies; PUSH/POP interact with the stack pointer and memory.Exclude arithmetic: No addition, subtraction, or multiplication occurs.Exclude control flow: No jumps, calls, or branches.Conclude category: Data transfer. Verification / Alternative check: Instruction set references classify these as move/stack operations under data transfer. Why Other Options Are Wrong: Arithmetic: Not performing math.Bit manipulation: Not directly setting/clearing bits.Loops and jumps: Not altering instruction flow. Common Pitfalls: Thinking PUSH/POP are control flow because of their association with CALL/RET; they themselves only move data. Final Answer: Data transfer

Question 18

Instruction classification: AND, OR, and TEST are members of which instruction category in typical processor ISAs?

Accepted Answer

Introduction / Context: Logical operations form a separate class from arithmetic in many instruction sets. They are essential for masking, flag testing, and condition formation. This question asks which category includes AND, OR, and TEST. Given Data / Assumptions: AND and OR perform bitwise logic between operands. TEST performs a bitwise AND without storing the result, updating flags for conditional decisions. No addition or subtraction is implied. Concept / Approach: Because these operations change or evaluate bits directly, they are categorized under logical/bit manipulation instructions rather than arithmetic or control flow. Step-by-Step Solution: Recognize bitwise nature of AND/OR.Recall that TEST updates flags based on an AND operation.Match to the “bit manipulation / logical” class.Select “Bit manipulation.” Verification / Alternative check: Architecture manuals list AND/OR/TEST among logical/bit operations (often with XOR, NOT, shifts, and rotates). Why Other Options Are Wrong: Data transfer: These do not move data between locations.Arithmetic: No numeric addition/subtraction/multiplication.Loops and jumps: Not altering control flow. Common Pitfalls: Assuming TEST is arithmetic because it affects flags; it is still a bitwise logic evaluation. Final Answer: Bit manipulation

Question 19

Instruction classification: ADD, CMP, and MUL belong to which category of instructions in common CPU instruction sets?

Accepted Answer

Introduction / Context: Arithmetic instructions manipulate numeric values, influencing flags that guide conditional execution. This question asks you to place three well-known instructions into their correct category. Given Data / Assumptions: ADD performs integer addition and sets flags like carry and zero as appropriate. CMP subtracts operands to set flags but discards the result, enabling comparisons. MUL multiplies operands and sets flags/expands results according to the ISA. Concept / Approach: All three affect numeric state or flags in a way tied to arithmetic semantics, so they are grouped under arithmetic rather than data movement or control flow. Step-by-Step Solution: Identify ADD and MUL as straightforward arithmetic.Recognize CMP as arithmetic comparison via subtraction without storing.Map to the “Arithmetic” instruction class.Choose “Arithmetic.” Verification / Alternative check: Instruction set documents categorize ADD/MUL/CMP with arithmetic/logic, distinct from data transfer and control operations. Why Other Options Are Wrong: Data transfer: No movement between locations is primary.Bit manipulation: Not purely logical masking or shifting.Loops and jumps: No branch or jump semantics. Common Pitfalls: Misclassifying CMP because it stores no result; its sole purpose is arithmetic comparison via flags. Final Answer: Arithmetic

Question 20

Software structuring in assembly and high-level languages: A small program unit written once and invoked multiple times from different places in a larger program is commonly called a(n) ________.

Accepted Answer

Introduction / Context: Code reuse and modularity are central to software engineering. In assembly and higher-level languages alike, programmers encapsulate a repeated operation in a callable unit so that it is written once and used many times, reducing duplication and improving maintainability. Given Data / Assumptions: The construct can be invoked from multiple points in the program. Control returns to the caller after execution (unless specified otherwise). It may use parameters and return values or registers according to calling conventions. Concept / Approach: The standard term for such a reusable program unit is “subroutine.” In various languages, equivalent terms include function, procedure, method, or routine. In assembly, CALL transfers control to the subroutine; RET returns to the caller, often using the stack for return addresses and parameters. Step-by-Step Solution: Identify the requirement: write once, call many times.Map to terminology: subroutine/function/procedure.Note call/return mechanism via stack or linkage register.Select “subroutine.” Verification / Alternative check: Programming texts and ABIs define subroutines with calling conventions (parameter passing, register saving, return values). Why Other Options Are Wrong: string: A data structure, not executable code.interrupt: An asynchronous event/handler mechanism triggered by hardware or software, not a normal reusable routine.processor control: A vague phrase; not the standard term here. Common Pitfalls: Confusing interrupts with normal calls; mixing “macro” (textual expansion) with subroutines (single copy executed via call). Final Answer: subroutine

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