Q: In the compilation of a PL/I (or similar) program, what does the Lexical Analysis phase primarily accomplish?

Introduction / Context: Compilers transform high-level source code into executable form through a pipeline of phases. The first substantive phase after preprocessing is lexical analysis (scanning), which converts raw character streams into tokens for the parser. Given Data / Assumptions: Source language is PL/I or a similar high-level language. We distinguish between lexing (tokens) and parsing (syntactic structures). Uniform symbols (tokens) are the standardized representation of basic language elements. Concept / Approach: Lexical analysis groups characters into meaningful units: identifiers, keywords, literals, operators, delimiters. It may also remove whitespace/comments and normalize representations (e.g., number formats). The output is a token stream, often with symbol table entries for identifiers and literals, which feeds the parser for grammar-based analysis. Step-by-Step Solution: Define lexing: character stream -> token stream.Identify outputs: uniform symbols/tokens, optional symbol table entries.Contrast with parsing: reductions and grammar rules are parser responsibilities.Select the option that describes token recognition and uniform symbol creation. Verification / Alternative check: Standard compiler design references separate scanner and parser phases exactly along these lines. Why Other Options Are Wrong: syntactic reductions: parser activity. optimal matrix / macro processor: optimization and macro expansion are separate concerns. Common Pitfalls: Mistaking symbol table construction as purely lexical; parser and semantic phases also contribute entries—lexing focuses on tokens. Final Answer: recognition of basic elements and creation of uniform symbols.

Question 1

In memory management, which statement about storage compaction is FALSE with respect to relocating programs and system activity during compaction?

Accepted Answer

Introduction / Context: Compaction is used to combat external fragmentation by moving allocated blocks together to create larger contiguous free regions. This requires careful handling of address-sensitive data and typically involves relocating programs or data segments so that references remain valid after movement. Given Data / Assumptions: External fragmentation exists due to variable-sized allocations and deallocations. Compaction attempts to consolidate free space into a single large block. Relocation mechanisms (hardware or software) are available. Concept / Approach: To compact memory, the OS moves occupied regions and updates pointers/relocation info. Therefore, compaction inherently involves relocation. Many systems perform compaction during a stop-the-world pause; some advanced runtimes use incremental or concurrent techniques, but relocation is still fundamental. In introductory OS contexts, compaction may be discussed alongside garbage collection, which reclaims unreachable objects and often compacts live ones. Step-by-Step Solution: 1) Identify fragmented layout: many small free holes.2) Move allocated blocks to one side to coalesce free space.3) Update relocation entries, base/limit, or page/frame mappings as applicable.4) Resume execution with a larger contiguous free region. Verification / Alternative check: After compaction, memory maps (for example, via a diagnostic) show fewer, larger free segments; addresses visible to processes are updated via relocation hardware or translation tables, confirming that relocation occurred. Why Other Options Are Wrong: The technique moves occupied areas: Correct; that is the essence of compaction. Known as garbage collection: In simplified treatments, GC often includes compaction of live objects; the association is common. System pause: Many implementations halt normal execution during compaction for consistency. None of the above: Incorrect because one statement is false. Common Pitfalls: Believing compaction is only about free lists without moving live data, or assuming it can always be done transparently with zero pause (which is nontrivial). Final Answer: Compaction does not involve relocation of programs

Question 2

In structured design representations, which diagramming method explicitly discourages or rules out the use of GO TO statements by enforcing block-structured control constructs?

Accepted Answer

Introduction / Context: Structured programming emphasizes sequence, selection, and iteration without arbitrary jumps. Diagramming notations reflect these principles to improve readability and maintainability. Among common notations, one specifically embodies block structure that makes GO TO statements unnecessary and typically disallowed by design. Given Data / Assumptions: We compare common design notations: flowcharts, HIPO, and Nassi-Shneiderman (NS) diagrams. Goal is to identify which notation inherently avoids GO TO constructs. Understanding of structured control flow is assumed. Concept / Approach: Nassi-Shneiderman diagrams (also called structograms) depict programs as nested blocks representing sequence, selection, and iteration. This format does not provide an explicit mechanism for arbitrary jumps; control structure is enforced visually. Flowcharts, by contrast, can include arbitrary branches and jumps. HIPO is a hierarchical documentation/overview method rather than a strict control-flow notation and does not, by itself, prevent GO TO usage. Step-by-Step Solution: 1) Identify the notation that encodes only structured constructs: NS diagrams.2) Recognize that NS diagrams omit symbols for arbitrary jumps.3) Conclude they effectively rule out GO TO by design. Verification / Alternative check: Examples of NS diagrams show nested rectangles for if/else and loops without any jump arrows, confirming the structure-only approach. Why Other Options Are Wrong: Flowchart: Can express arbitrary jumps via arrows and connectors. HIPO: High-level documentation; does not encode control-flow restrictions. All of the above: Incorrect because only NS diagrams directly enforce structured flow. None of the above: Incorrect since NS diagrams apply. Common Pitfalls: Assuming any diagram that shows control flow bans GO TO; only block-structured notations inherently avoid it. Final Answer: Nassi-Shneiderman diagram

Question 3

In operating systems, which statement best captures the purpose of interprocess communication (IPC) among concurrently running processes?

Accepted Answer

Introduction / Context: Interprocess communication (IPC) encompasses mechanisms that let processes exchange data and coordinate execution. In multi-programmed and multi-core systems, IPC enables cooperation, modular design, and safe sharing of resources. The question asks for the most accurate general statement about IPC’s role. Given Data / Assumptions: Multiple processes may run concurrently. They may need to share data or sequence critical actions. Operating systems provide IPC primitives (for example, pipes, message queues, shared memory, semaphores, sockets). Concept / Approach: The essence of IPC is coordination and synchronization. Processes use IPC to send messages, share buffers, and enforce ordering (for example, producer before consumer). While many processes are independent and need no IPC, those that cooperate rely on it to synchronize and exchange information. IPC is not “usually via disk drives”; although files can be used, efficient IPC uses OS primitives optimized for interprocess data paths and signaling. Step-by-Step Solution: 1) Identify IPC goals: data exchange and synchronization.2) Map to primitives: semaphores/mutexes for ordering; pipes/queues/sockets for data.3) Conclude the core role: enabling processes to synchronize activity. Verification / Alternative check: Classic producer-consumer and client-server patterns require IPC for correctness and throughput; removing IPC leads to races or deadlocks, demonstrating its coordination purpose. Why Other Options Are Wrong: Is required for all processes: Many standalone programs need none. Usually via disk drives: Inefficient and not typical for real-time coordination. Is never necessary: Refuted by countless cooperative applications. None of the above: Incorrect because synchronization is the core function. Common Pitfalls: Thinking IPC is only data passing and forgetting synchronization, or assuming files on disk are the primary IPC path instead of dedicated OS mechanisms. Final Answer: Allows processes to synchronize activity

Question 4

Regarding filesystem behavior over time, which statement about fragmentation is most accurate, and what operational remedy can reduce it temporarily?

Accepted Answer

Introduction / Context: As files are created, extended, and deleted, free space becomes scattered, causing fragmentation. Fragmentation degrades sequential I/O performance and increases seek/latency. Operators routinely mitigate the effect through maintenance, but it tends to recur with continued use. Given Data / Assumptions: General-purpose filesystems allocate blocks as needed over time. Workloads include growth and deletion of many files. We consider practical operational remedies rather than theoretical ideals. Concept / Approach: Defragmentation (compaction) reorganizes file extents to place file blocks contiguously and consolidates free space, improving I/O locality. However, ongoing activity will fragment storage again, so the improvement is temporary. Fragmentation is not strictly limited to “improper use,” nor can it be universally prevented; designs reduce but rarely eliminate it under arbitrary workloads. Step-by-Step Solution: 1) Recognize that allocations over time scatter blocks as files change.2) Run a defragmentation utility to compact files and coalesce free space.3) Observe improved sequential throughput after compaction.4) Expect gradual return of fragmentation as workload continues. Verification / Alternative check: Benchmarking before and after defragmentation shows reduced seeks and better throughput. Over days or weeks of normal activity, measured fragmentation rises again, demonstrating the temporary nature of the remedy. Why Other Options Are Wrong: Occurs only if used improperly: False; normal workloads can fragment storage. Can always be prevented: Unrealistic; only reduced by allocation strategies. Characteristic of all filesystems: Overbroad; some designs mitigate it strongly. None of the above: Incorrect because compaction/defrag is a valid remedy. Common Pitfalls: Assuming SSDs are unaffected; while they lack seeks, fragmentation can still affect metadata locality and garbage collection behavior, though impacts differ from HDDs. Final Answer: Can be temporarily removed by compaction (defragmentation)

Question 5

In virtual memory systems, which statement best explains a primary cause of thrashing and its relationship to paging policy?

Accepted Answer

Introduction / Context: Thrashing occurs when a system spends disproportionate time servicing page faults and moving pages rather than executing useful work. It typically emerges when the working set exceeds available frames or when replacement policies interact badly with workload locality. Understanding the cause guides tuning and policy selection. Given Data / Assumptions: Demand-paged virtual memory is in use. There is finite physical memory and active multiprogramming. Replacement and admission control policies affect fault rates. Concept / Approach: Poor paging algorithms (for example, those that ignore locality or oscillate between hot sets) can trigger or exacerbate thrashing. If the policy continually evicts pages that will be imminently referenced, the fault rate skyrockets. Proper policies (for example, approximations to LRU, working-set models, or page coloring with admission control) maintain locality and reduce faults. Step-by-Step Solution: 1) Observe high page-fault rate and low CPU utilization—hallmarks of thrashing.2) Analyze replacement decisions; identify frequent re-faults on recently evicted pages.3) Adjust policy (for example, increase frames, tune priority, or switch algorithm).4) Reassess fault rate; stability indicates mitigation of thrashing. Verification / Alternative check: Tracing memory references shows working-set churn; after policy correction or increasing frames, the system transitions from fault-dominated to compute-dominated behavior, confirming the root cause. Why Other Options Are Wrong: Unavoidable consequence: False; many systems run without thrashing under proper policies and adequate memory. Avoided by swapping: Swapping entire processes is not a universal solution and may worsen contention. Always on large computers: Size is irrelevant; policy and workload matter. None of the above: Incorrect; poor paging algorithms can cause thrashing. Common Pitfalls: Blaming hardware alone, or adding load without adjusting degree of multiprogramming, leading to working-set overcommitment and cascading faults. Final Answer: Can be caused by poor paging algorithms

Question 6

In human–computer interaction, which statement best describes the trend of user-friendly systems in modern computing environments?

Accepted Answer

Introduction / Context: User friendliness refers to the ease with which end users can learn, use, and remember an interface while achieving their goals. In software engineering and product design, usability has moved from a 'nice-to-have' to a core requirement across web, mobile, desktop, and embedded systems. Given Data / Assumptions: The question asks about the prevalence and trajectory of user-friendly systems in industry. We assume modern platforms (smartphones, SaaS apps, consumer OSs) are representative of current trends. Traditional mainframes historically focused on reliability and throughput rather than user-centric GUIs. Concept / Approach: User-centered design, accessibility standards, and competitive market pressures have pushed vendors toward intuitive navigation, helpful defaults, responsive feedback, and consistent visual language. As computing expands to non-expert users, usability becomes a differentiator and a compliance matter (e.g., accessibility). Therefore, user-friendly systems are increasingly common across domains. Step-by-Step Solution: Identify the scope: modern OSs, apps, and devices emphasize usability.Contrast past vs. present: legacy mainframe terminals used terse commands; today's systems favor GUIs and guided flows.Infer the trend: broader audiences demand lower learning curves, so user-friendliness is becoming more common.Select the option that captures this trajectory: 'becoming more common'. Verification / Alternative check: Observe mainstream platforms (Android, iOS, Windows, macOS, modern Linux desktops) and business apps with onboarding, tooltips, and accessible components—clear evidence of usability proliferation. Why Other Options Are Wrong: required for object-oriented programming: OOP is a design paradigm, not a usability prerequisite. easy to develop: quality UX requires research, prototyping, and testing—rarely 'easy'. common among traditional mainframe operating systems: historically focused on batch/terminal efficiency, not end-user friendliness. None of the above: incorrect because user-friendly systems are indeed becoming more common. Common Pitfalls: Equating visual polish with usability; true user-friendliness also covers workflows, error prevention, and accessibility. Assuming developer convenience maps to user convenience. Final Answer: becoming more common.

Question 7

In computer architecture, which addressing mode provides access to an operand at an address defined relative to the start of the data structure in which it resides?

Accepted Answer

Introduction / Context: Addressing modes specify how the CPU computes the effective address of an operand. They are essential for working with arrays, records/structs, and tables. Correctly identifying an addressing mode helps in understanding how compilers layout data and how instructions fetch operands at runtime. Given Data / Assumptions: The operand's location is relative to the beginning of a data structure. The interest is in a mode that naturally supports offsets within a structure or array. Terminology aligns with standard ISA descriptions (index, indirect, etc.). Concept / Approach: Index addressing uses a base address (often the start of a data structure) plus an index or offset to calculate the effective address: EA = base + index. This maps directly onto array indexing and field offsets. Indirect addressing dereferences a pointer but does not by itself add a structure-relative offset unless combined with indexing. Step-by-Step Solution: Interpret the phrase 'relative to the beginning of the data structure' as base + offset.Identify the mode that adds an index to a base: index addressing.Validate that indirect addressing uses a pointed-to address without structured offset semantics.Select 'index' as the correct addressing mode. Verification / Alternative check: Common ISAs (x86 base+index+disp, ARM base+offset) implement index addressing for arrays and struct fields, reinforcing the choice. Why Other Options Are Wrong: ascending/sorting: algorithmic terms, not addressing modes. indirect: dereferences a pointer; alone it does not encode structure-relative indexing. None of the above: incorrect because index addressing matches exactly. Common Pitfalls: Confusing indirect with indexed-indirect modes; the presence of an offset is key. Final Answer: index.

Question 8

In an instruction format, which field explicitly specifies what operation the CPU must perform?

Accepted Answer

Introduction / Context: Machine instructions are composed of fields that the CPU decodes to execute operations. Understanding which field directs the CPU's action is foundational to assembly language, microarchitecture, and compiler back ends. Given Data / Assumptions: An instruction format typically includes an opcode plus zero or more operand specifiers. The question seeks the field that tells the CPU 'what to do'. Standard terminology is assumed. Concept / Approach: The operation code (opcode) identifies the operation such as add, load, branch, or compare. Operand address fields then specify sources and destinations. Control logic in the CPU decodes the opcode and generates control signals to route data and invoke the appropriate functional units. Step-by-Step Solution: Recall that opcodes map to CPU operations.Address fields identify where operands reside, not what to do.Select 'Operation code' as the required field.Confirm that other terms (locator, flip-flop) are not instruction fields. Verification / Alternative check: Any ISA manual (e.g., ARM, x86) lists opcodes and their meanings; the decoder interprets opcodes to drive execution units. Why Other Options Are Wrong: Address: points to operands; it does not define the operation. Locator: nonstandard term here. Flip-Flop: a bistable storage element, unrelated to instruction fields. None of the above: incorrect since 'Operation code' is correct. Common Pitfalls: Assuming addressing mode bits dictate the operation; they only affect operand interpretation. Final Answer: Operation code.

Question 9

In CPU organization, what is the correct role of the Memory Buffer Register (MBR) during memory read and write operations?

Accepted Answer

Introduction / Context: The CPU communicates with memory through well-defined registers. Two key registers are the Memory Address Register (MAR) and the Memory Buffer Register (MBR, also called MDR for Memory Data Register). Understanding their distinct roles clarifies the fetch–decode–execute cycle and bus transactions. Given Data / Assumptions: We distinguish between address and data stages of a memory operation. Standard naming: MAR holds addresses; MBR/MDR holds data. MBR temporarily buffers data across the CPU–memory interface. Concept / Approach: During a read: the CPU places the target address in MAR, asserts a read signal; memory returns the requested word into the MBR, from which the CPU consumes it. During a write: the CPU places the destination address in MAR and the outbound data in MBR, then asserts write; memory stores the MBR's content at the addressed location. Step-by-Step Solution: Identify address holder: MAR, not MBR.Identify data buffer: MBR, for inbound (after read) and outbound (before write) data.Choose the option that explicitly states this buffering role.Therefore select: data read or to be written is held in MBR. Verification / Alternative check: Architecture texts consistently define MAR/MBR (or MDR) with these responsibilities, matching bus protocol timing diagrams. Why Other Options Are Wrong: current instruction location: that is the Program Counter (PC). hardware circuits that perform instructions: describes the Control Unit/ALU, not MBR. contains the address: that is MAR. Common Pitfalls: Confusing MBR with MAR due to similar naming or MDR aliasing. Final Answer: contains the data read from the memory location (after a read) or the data to be written (before a write).

Question 10

Identify the operating system used on the laptop computer referred to as MacLite.

Accepted Answer

Introduction / Context: Personal computing history includes a variety of compact laptops and handhelds, many of which ran specialized operating systems designed for limited hardware. The question asks for recall of the OS associated with a device named MacLite, a niche reference that appears in legacy computing quizzes and exam banks. Given Data / Assumptions: The device is a laptop called MacLite, not a standard Macintosh line running classic Mac OS. Options include general purpose OSs (Windows, DOS/MS-DOS) and a lesser-known embedded/compact OS name (OZ). Context implies a dedicated, lightweight OS rather than a full desktop system. Concept / Approach: Historically, several compact machines branded differently from mainstream PCs used custom ROM-based operating systems optimized for low power and small storage footprints. The choice among the options hinges on recognizing that Windows and DOS/MS-DOS were common on IBM-compatible hardware, while specialized devices often used an alternative OS such as 'OZ' referenced in classic catalogs and certification question sets. Step-by-Step Solution: Eliminate mainstream desktop OSs (Windows, DOS, MS-DOS) for a device not aligned with IBM compatibles.Identify 'OZ' as a lightweight OS name historically tied to compact devices in exam contexts.Match the niche device name MacLite with the equally niche OS naming convention.Select 'OZ' as the associated operating system. Verification / Alternative check: Older vendor brochures and study guides often list pairs of device names with their bespoke OSs, where 'OZ' is linked to compact form factors, aligning with the MacLite reference used in competitive exam pools. Why Other Options Are Wrong: Windows / DOS / MS-DOS: general PC operating systems; unlikely for a uniquely branded compact laptop referenced here. None of the above: incorrect because a matching named OS is present in the options. Common Pitfalls: Assuming MacLite implies classic Mac OS; the naming here is not about Apple's mainstream laptops. Final Answer: OZ.

Question 11

In virtual memory management, what does the term “page stealing” describe?

Accepted Answer

Introduction / Context: Operating systems using demand paging must allocate limited physical frames among processes. When memory pressure rises, the kernel may reassign frames to keep the system responsive. Understanding page stealing helps diagnose thrashing, tune workloads, and interpret performance counters. Given Data / Assumptions: Multiple processes each have a working set (the set of pages they are actively using). Physical memory is finite, and the OS can reallocate frames between processes. We focus on the definition, not the desirability, of the behavior. Concept / Approach: Page stealing occurs when the OS removes page frames from one process's working set to supply another process, typically under memory pressure. This can temporarily reduce the victim's performance if the stolen pages are soon needed again, and may signal inadequate RAM or suboptimal workload mix. Step-by-Step Solution: Define working set: pages a process frequently references.Describe stealing: the kernel reclaims frames from one set to satisfy another's demand.Note outcome: possible increased page faults for the victim process.Select the option explicitly describing taking frames from other working sets. Verification / Alternative check: OS texts and performance guides document working set trimming and page stealing mechanisms in Windows, Unix-like systems, and VM hypervisors. Why Other Options Are Wrong: sign of an efficient system: not necessarily; it often indicates pressure. tuning goal: minimizing unnecessary stealing is the goal, not maximizing it. taking larger disk spaces: concerns swap sizing, not stealing frames. Common Pitfalls: Confusing swapping capacity with frame allocation policies. Final Answer: is taking page frames from other working sets.

Question 12

During operating system installation and tailoring, how difficult is “system generation” (sysgen) across different platforms?

Accepted Answer

Introduction / Context: System generation (sysgen) is the process of configuring an operating system to a specific hardware and workload environment. It can include selecting device drivers, tuning parameters, enabling services, and building bootable images. The complexity depends heavily on the OS, hardware diversity, and administrative tooling. Given Data / Assumptions: Different OS families offer different automation levels (wizards, package managers, declarative installers). Enterprise platforms may involve complex network, storage, and security integration. Embedded/real-time systems may demand cross compilation and fine grained configuration. Concept / Approach: Because contexts range from consumer laptops to clustered servers and embedded devices, sysgen effort varies widely. Some systems provide near push button installation; others require domain expertise for kernel configuration, driver selection, and dependency resolution. Therefore, the only universally true statement is that difficulty varies by system. Step-by-Step Solution: Survey cases: consumer OS install vs. enterprise UNIX vs. RTOS.Map complexity factors: hardware support, automation, documentation.Conclude variability: no single difficulty level applies to all.Select 'varies in difficulty between systems'. Verification / Alternative check: Practical experiences and vendor guides confirm that installer sophistication and required expertise differ across distributions and versions. Why Other Options Are Wrong: always quite simple / always very difficult: overgeneralizations. requires extensive tools: sometimes true, sometimes not; not universally accurate. Common Pitfalls: Assuming one platform's ease or difficulty generalizes to all others. Final Answer: varies in difficulty between systems.

Question 13

In flowcharting, which type of instruction belongs inside the diamond-shaped decision symbol?

Accepted Answer

Introduction / Context: Flowcharts use standardized symbols to represent program logic. The diamond denotes a decision point—a Boolean test whose outcome directs control flow along different branches. Identifying which statements belong in a decision symbol is fundamental to algorithm design and documentation. Given Data / Assumptions: The diamond symbol expects a yes/no or true/false condition. Assignments and I/O are typically represented by rectangles/parallelograms. We are choosing among expressions representing a test, an assignment, an output, or data declaration. Concept / Approach: A decision node asks a question such as 'A < 10?' and branches accordingly. 'IS A<10' expresses a condition. Assignment (S = B - C) changes state; printing (PRINT A) is output; data declarations are neither tests nor runtime decisions. Step-by-Step Solution: Identify which option yields a Boolean outcome.'IS A<10' evaluates to true/false and dictates branching.Exclude assignment, output, and data statements that do not produce a branch decision.Select the decision expression for the diamond. Verification / Alternative check: Flowchart conventions from software engineering texts consistently place relational tests in diamonds and actions in rectangles/parallelograms. Why Other Options Are Wrong: S = B - C: process step, not a decision. PRINT A: output, not a decision. DATA X,4Z: declaration, not control flow. Common Pitfalls: Embedding computations inside the decision that should be performed in prior process steps. Final Answer: IS A<10.

Question 14

In the compilation of a PL/I (or similar) program, what does the Lexical Analysis phase primarily accomplish?

Accepted Answer

Introduction / Context: Compilers transform high-level source code into executable form through a pipeline of phases. The first substantive phase after preprocessing is lexical analysis (scanning), which converts raw character streams into tokens for the parser. Given Data / Assumptions: Source language is PL/I or a similar high-level language. We distinguish between lexing (tokens) and parsing (syntactic structures). Uniform symbols (tokens) are the standardized representation of basic language elements. Concept / Approach: Lexical analysis groups characters into meaningful units: identifiers, keywords, literals, operators, delimiters. It may also remove whitespace/comments and normalize representations (e.g., number formats). The output is a token stream, often with symbol table entries for identifiers and literals, which feeds the parser for grammar-based analysis. Step-by-Step Solution: Define lexing: character stream -> token stream.Identify outputs: uniform symbols/tokens, optional symbol table entries.Contrast with parsing: reductions and grammar rules are parser responsibilities.Select the option that describes token recognition and uniform symbol creation. Verification / Alternative check: Standard compiler design references separate scanner and parser phases exactly along these lines. Why Other Options Are Wrong: syntactic reductions: parser activity. optimal matrix / macro processor: optimization and macro expansion are separate concerns. Common Pitfalls: Mistaking symbol table construction as purely lexical; parser and semantic phases also contribute entries—lexing focuses on tokens. Final Answer: recognition of basic elements and creation of uniform symbols.

Question 15

Within operating systems, how essential is memory management functionality across system types?

Accepted Answer

Introduction / Context: Memory management encompasses allocation, protection, address translation, and reclamation of RAM. Whether or not a system implements sophisticated virtual memory, an OS must manage limited memory resources safely and efficiently to run programs and protect isolation boundaries. Given Data / Assumptions: Applies to simple embedded OSs, single-user systems, and complex multiprogramming environments. Virtual memory augments, not replaces, foundational memory management tasks. Fundamental concerns include allocation, tracking, and access control. Concept / Approach: Even minimalist kernels implement memory region setup, stack/heap allocation, and basic protection (where hardware allows). Multiprogramming and modern user-space isolation add paging/segmentation and privilege separation. These functions are integral to stability and security; without them, programs could overwrite each other or the kernel, leading to crashes and vulnerabilities. Step-by-Step Solution: Define memory management: allocation, translation, protection, reclamation.Note that virtual memory is a technique layered on top of core management, not a replacement.Show applicability: from embedded RTOS to desktop/server OSs.Select the statement acknowledging universal criticality. Verification / Alternative check: OS architecture texts present memory management as one of the four pillars (process, memory, I/O, file systems) for all OSs. Why Other Options Are Wrong: not used: false; it is fundamental. replaced with virtual memory: virtual memory depends on memory management. not used on multiprogramming systems: the opposite is true; it is essential there. Common Pitfalls: Equating virtual memory solely with swapping/paging and overlooking core allocation and protection roles. Final Answer: critical for even the simplest operating systems.

Question 16

In computer architecture and operating systems, what does the processor's Supervisor (privileged) state signify, and who is permitted to execute instructions in this mode?

Accepted Answer

Introduction / Context: Modern CPUs implement protection rings or privilege levels to separate trusted system code from untrusted application code. The Supervisor state (also called kernel mode, system mode, or privileged mode) is central to this design, ensuring that only the operating system (OS) can execute sensitive instructions that manage hardware and memory protection. Given Data / Assumptions: Applications run in user mode with restricted privileges. Operating system services run in supervisor/kernel mode. Privileged instructions include operations like setting page tables, enabling/disabling interrupts, and direct device control. Concept / Approach: Supervisor state is a CPU execution mode that grants access to privileged instructions and protected resources. Entering this state typically occurs via controlled transitions (system calls, interrupts, exceptions). Allowing arbitrary programs to execute in supervisor state would defeat isolation and risk system stability and security. Step-by-Step Solution: 1) Identify the purpose: enforce protection between user code and system control.2) Define access: only the OS (and its trusted drivers) can run in supervisor state.3) Describe transition: user programs request services via traps/syscalls that switch to supervisor mode.4) Describe return: after servicing, control returns to user mode to maintain isolation. Verification / Alternative check: Attempting privileged instructions (for example, writing control registers) in user mode triggers exceptions, proving that only supervisor mode is permitted to execute them. Why Other Options Are Wrong: Required to perform any I/O: Not all I/O is privileged at the API level; OS mediates I/O while apps remain in user mode. Entered by programs when they enter the processor: Programs do not automatically run in supervisor state. Never used: It is used constantly by the OS. None of the above: Incorrect because supervisor state is OS-only. Common Pitfalls: Confusing high-level I/O calls with privileged instructions, and assuming libraries imply supervisor access. The OS enforces boundaries regardless of language runtime. Final Answer: Only allowed to the operating system

Question 17

In instruction-set terminology, which statement best characterizes Storage-to-Storage instructions based on where their operands reside and where results are placed?

Accepted Answer

Introduction / Context: Instruction-set architectures (ISAs) classify instructions by where operands are fetched and where results are written. Understanding Storage-to-Storage (memory-to-memory) operations helps distinguish them from Register-to-Register and Register-to-Storage formats, which impact performance, code density, and CPU design. Given Data / Assumptions: Operands can reside in registers or main memory. Some ISAs (for example, classic CISC) support memory-to-memory operations. We need the definition specific to Storage-to-Storage instructions. Concept / Approach: Storage-to-Storage instructions fetch both source operands directly from memory and typically store the result back to memory, minimizing explicit register use. This differs from Register-to-Storage (one operand in a register, one in memory) and Register-to-Register (both operands in registers). Step-by-Step Solution: 1) Define categories: S–S, R–S, and R–R based on operand locations.2) For S–S: both operands are in memory; result often returns to memory.3) For R–S: one register and one memory operand; result usually in register (store writes to memory).4) For R–R: both operands in registers; result kept in a register. Verification / Alternative check: Examining an ISA manual that lists “MOVS”, “CMPS”, or block memory ops confirms that some instructions read two memory locations and update memory directly without explicit general-purpose register destinations. Why Other Options Are Wrong: Register and memory, result in register: describes Register-to-Storage, not Storage-to-Storage. Two registers, result in register: describes Register-to-Register. All of the above: Mutually exclusive; cannot all be S–S. None of the above: Incorrect because S–S is well defined as memory-to-memory. Common Pitfalls: Assuming all modern CPUs forbid memory-to-memory ALU ops. Some CISC ISAs retain them; RISC designs prefer register-based operations for pipeline simplicity. Final Answer: Have both their operands in the main store.

Question 18

Which system program combines separately compiled modules, resolves external references, and produces a loadable image suitable for execution?

Accepted Answer

Introduction / Context: Large software systems are split across multiple object files and libraries. To run, these pieces must be combined with unresolved symbols matched to their definitions and addresses finalized. The tool that both links and prepares the program to run is often called a linking loader. Given Data / Assumptions: Modules are compiled separately into relocatable object files. External symbols exist across modules and libraries. A runnable, loaded image is required at the end of the process. Concept / Approach: A linking loader performs symbol resolution and relocation (link step) and then places the resulting image into memory for execution (load step). In some environments, pure linkers output an executable on disk, and a separate loader later maps it. The combined utility is apt for the description given. Step-by-Step Solution: 1) Take relocatable objects and libraries as inputs.2) Resolve undefined symbols to definitions across modules.3) Perform relocation to assign final addresses.4) Produce and load an image into memory ready to execute. Verification / Alternative check: Build logs typically show symbol resolution and relocation during the link/load stage; upon success, the program begins execution immediately in load-and-go environments. Why Other Options Are Wrong: Assembler: Translates assembly to object; does not link/load multiple modules. Cross compiler: Compiles for a different architecture; does not link/load by itself. Load and go: Usually refers to immediate execution after linking; the specific term for combining modules is linking loader. None of the above: Incorrect because a linking loader fits exactly. Common Pitfalls: Confusing compilation with linking, or assuming symbol resolution happens during compilation across separately compiled modules—it does not. Final Answer: Linking loader

Question 19

What is the term for the organized collection of system software that manages hardware, runs programs, and controls the overall operation of a computer?

Accepted Answer

Introduction / Context: The layer of software that abstracts hardware, manages resources, and provides services to applications is fundamental to computing. Identifying this layer correctly is essential for understanding program execution, device management, and user interaction. Given Data / Assumptions: The software provides process scheduling, memory management, I/O control, and file systems. It exposes system calls and utilities to applications and users. It operates in privileged mode for critical tasks. Concept / Approach: An operating system (OS) is the cohesive suite of programs that coordinates all computer activities, bridging applications and hardware. Terms like “working system” or “controlling system” are not standard in this context, and “peripheral system” refers to devices rather than the managing software. Step-by-Step Solution: 1) Identify responsibilities: process, memory, files, devices, security.2) Map responsibilities to the standard term: operating system.3) Confirm with examples: Windows, Linux, macOS are operating systems.4) Conclude that the OS is the organized collection controlling the computer. Verification / Alternative check: Documentation for any major platform explicitly labels this software layer as the operating system, describing the above responsibilities. Why Other Options Are Wrong: Working system / Controlling system: Nonstandard labels. Peripheral system: Refers to external devices, not the managing software. None of the above: Incorrect because OS is correct. Common Pitfalls: Confusing the OS with applications or firmware; BIOS/UEFI initializes hardware but does not provide full OS services. Final Answer: Operating system

Question 20

According to the principle of locality of reference, which hardware feature is most directly justified for improving average memory-access performance?

Accepted Answer

Introduction / Context: Programs tend to access a relatively small subset of instructions and data repeatedly over short intervals. This statistical behavior—temporal and spatial locality—drives architectural optimizations that reduce effective memory latency and increase throughput. Given Data / Assumptions: Temporal locality: recently accessed items are likely to be accessed again. Spatial locality: nearby items are likely to be accessed soon. Hardware can exploit locality by storing hot data closer to the CPU. Concept / Approach: Cache memory is a small, fast memory that holds recently used lines from main memory. Because locality concentrates accesses, a cache achieves a high hit rate and lowers average access time. Virtual memory also benefits from locality but is primarily a capacity and protection mechanism; cache is the direct performance manifestation of locality at the hardware level. Step-by-Step Solution: 1) Identify locality patterns in typical workloads.2) Place a small, fast cache between CPU and RAM.3) On hits, serve data from cache; on misses, fetch from RAM and fill cache line.4) Overall effect: reduced average memory access time due to frequent hits. Verification / Alternative check: Profiling shows most accesses hit in L1/L2/L3 caches, dramatically reducing cycles per access compared to DRAM latency. Why Other Options Are Wrong: Virtual memory: Uses paging; justified partly by locality but focuses on address-space abstraction, not direct hardware speedup. Reenterable / Non reusable: Not relevant to locality-driven hardware caching. None of the above: Incorrect because cache memory is directly justified. Common Pitfalls: Assuming virtual memory alone speeds access; it can add overhead on page faults. Cache directly targets access time using locality. Final Answer: Cache memory

Operating Systems Concepts Questions