Question 1

Backup Strategy Basics  What is the most appropriate general strategy for scheduling backups in a typical installation to balance data safety and storage/time costs?

Accepted Answer

Introduction / Context: A sound backup plan seeks to minimize data loss (recovery point objective) while keeping restore times acceptable (recovery time objective). Pure daily full backups are safe but expensive; pure incremental backups save space but can slow restores. A balanced, widely used approach is to run several incrementals between periodic full (image) backups. Given Data / Assumptions: Typical mixed-use environment (files, documents, small databases). Desire to reduce backup windows and storage consumption. Need for quick restoration of current state within practical time. Concept / Approach: Combine full backups with a chain of incremental backups. The full backup captures the entire data set (a clean base). Incrementals capture only changes since the previous backup, reducing duration and storage. Periodically refreshing with another full backup shortens the chain used during restores, making recovery faster and more reliable. Step-by-Step Solution: Select a cadence: for example, weekly full + daily incremental.Full (image) backup establishes a baseline snapshot.Run incrementals on intervening days to capture changes.Repeat the cycle so that restores require at most one full plus a limited set of incrementals. Verification / Alternative check: Test restores periodically. Verify you can restore from the latest full plus subsequent incrementals to a known-good state. Measure restore time and ensure it meets business needs. Why Other Options Are Wrong: Daily full only (Option A) is safe but often impractical due to time/storage.Weekly only (Option B) risks too much data loss between backups.Fulls followed by a single incremental (Option C) inverts the efficient norm; you typically want several incrementals between fulls, not the reverse.“None of the above” is incorrect because Option D reflects the practical hybrid. Common Pitfalls: Not rotating fulls, causing long incremental chains and slow restores. Failing to verify backups through test restores. Storing backups only onsite, risking correlated loss. Final Answer: As several incrementals, followed by an image (full) copy.

Question 2

Operating Systems: Process States  In a multitasking operating system, a task (process/thread) that is in the blocked state is best described as:

Accepted Answer

Introduction / Context: Modern operating systems model program execution using process states such as new, ready, running, blocked (or waiting), and terminated. Understanding these states is crucial for debugging, performance tuning, and scheduling analysis. Given Data / Assumptions: Single or multi-CPU system with a scheduler and run queues. Blocked tasks are not consuming CPU but are part of the system state machine. Resources include I/O completion, locks, semaphores, timers, and interprocess messages. Concept / Approach: A blocked process cannot make progress until an external event occurs. Unlike a ready process, it should not be in the run queue. When the awaited event happens, the process transitions to ready and later to running when scheduled. Step-by-Step Solution: Identify resource dependency (e.g., disk I/O, network I/O, mutex).Process calls a blocking API or is descheduled upon contention.OS marks it blocked/waiting; it leaves the run queue.Upon event completion, OS transitions it to ready; the scheduler may then dispatch it. Verification / Alternative check: Use system tools (e.g., ps/top with state flags, Windows Resource Monitor) to observe threads waiting on I/O or synchronization primitives and note that they do not consume CPU in the interim. Why Other Options Are Wrong: Executable/ready (Option A) and running (Option B) contradict the waiting nature.Option C is incorrect; blocked processes are not in the run queue until the wait ends.“None of the above” is incorrect because Option D exactly defines blocked. Common Pitfalls: Confusing ready with blocked; only ready competes for CPU. Misdiagnosing CPU bottlenecks when the system is actually I/O-bound with many blocked tasks. Final Answer: Waiting for some temporarily unavailable resource.

Question 3

System Capability  Which capability is required for a system to execute more than one program at a time?

Accepted Answer

Introduction / Context: Running multiple programs concurrently requires operating system support and appropriate hardware scheduling. The umbrella term for this system ability is multitasking, which coordinates CPU time among processes/threads. Given Data / Assumptions: Time-sliced CPU with a scheduler. Processes or threads managed by the kernel. Possibly a single CPU (preemptive multitasking) or multiple CPUs (true parallelism). Concept / Approach: Distinguish features (applications) from system capabilities. Word processing and compiling are workloads, not enablers. Virtual memory is helpful but not strictly required to run more than one task; it provides address space isolation and over-commit handling. The defining capability is multitasking. Step-by-Step Solution: Identify OS services: process creation, scheduling, context switching.Assess whether multiple tasks can be runnable/ready simultaneously.Conclude that multitasking is the prerequisite capability. Verification / Alternative check: Observe a system monitor while multiple applications run; CPU time is shared among them via context switches—clear evidence of multitasking. Why Other Options Are Wrong: Word processing and compiling (Options A/B) are application types, not OS capabilities.Virtual memory (Option C) enhances protection/isolation but is not the sole requirement for simultaneity. Common Pitfalls: Assuming virtual memory equals multitasking; they address different concerns. Confusing multithreading (within one process) with multitasking (multiple processes). Final Answer: Multitasking.

Question 4

Mainframe Job Control  If special paper forms or printer handling are required for a batch job's output on classic systems, through what does the programmer specify these requirements?

Accepted Answer

Introduction / Context: On mainframe-class systems (e.g., IBM z/OS), batch jobs are orchestrated by Job Control Language (JCL), which describes resources, datasets, and device handling. Printing requirements such as forms control, destination, and class are traditionally specified in JCL statements. Given Data / Assumptions: Batch processing environment with spooling and print classes. Programmer controls device usage and output handling via control statements. Concept / Approach: JCL provides metadata about how to run a program, not the program logic itself. That includes printer queues, forms, and output classes. The job entry subsystem interprets these instructions, not the load module or generic utilities. Step-by-Step Solution: Define JOB and EXEC to specify unit of work and program to run.Use DD statements to describe datasets and output destinations.Include printer/form directives (class, forms number, destination) as part of JCL parameters. Verification / Alternative check: Referencing JES2/JES3 parameters shows how forms and routing are controlled in JCL and reflected in the spool before the print subsystem picks them up. Why Other Options Are Wrong: JPL (Option B) is not the standard control language in this context.Utility programs (Option C) perform tasks but do not replace JCL directives for device handling.Load modules (Option D) are executable artifacts, not job-control specifications. Common Pitfalls: Confusing application parameters with job control parameters. Forgetting to set correct form parameters causing print rejections or misprints. Final Answer: JCL (Job Control Language).

Question 5

Algorithm Design Basics  Which statement best describes pseudocode?

Accepted Answer

Introduction / Context: Pseudocode is a way to express algorithms in structured, human-readable steps without strict syntax. It bridges problem-solving and implementation, focusing on logic rather than machine or compiler rules. Given Data / Assumptions: Pseudocode is language-agnostic and not executable. Used for design, teaching, and communicating algorithmic intent. Not bound to CPU instruction sets or specific compilers. Concept / Approach: Differentiate pseudocode from real programming languages. Machine and assembly languages map directly to CPU instructions. High-level languages compile/interpret to machine code. Pseudocode remains descriptive and informal by design. Step-by-Step Solution: Assess Option A: Machine language is binary opcodes; pseudocode is not.Assess Option B: Assembly uses mnemonics and strict syntax; pseudocode does not.Assess Option C: High-level languages have defined grammar and compilers; pseudocode is free-form.Therefore, none of the above categorizations is accurate. Verification / Alternative check: Try to compile pseudocode in any compiler: it will fail unless translated into a specific language. This confirms pseudocode is a planning tool, not an implementation language. Why Other Options Are Wrong: A/B/C each asserts pseudocode is a formal language class; all are incorrect.D (All of the above) is impossible because A–C are mutually exclusive categories. Common Pitfalls: Writing pseudocode that is so language-specific it loses clarity. Implementing directly from unclear pseudocode and introducing logic errors. Final Answer: None of the above.

Question 6

Linking and Loading  In a relocating/absolute loading context, which tool generates the relocation (relocation/reallocation) bits used later by the loader?

Accepted Answer

Introduction / Context: During program preparation, tools produce metadata that enables code to be placed at varying memory locations. Relocation information (often called relocation bits/records) identifies addresses that must be adjusted when the program is loaded at a different base address. Given Data / Assumptions: Assembler and compilers translate source into object modules with relocation records. Loaders and linkers consume these records to adjust addresses. In absolute schemes, the assembler may produce absolute addresses; in relocating schemes, it emits relocation info. Concept / Approach: Separate producers of relocation info from consumers. Assemblers/translators know which references are relocatable and mark them. Linkers/loaders read these marks to fix up addresses at link or load time. Step-by-Step Solution: Source → assemble/compile → object file with relocation entries.Linker optionally resolves external symbols and performs partial relocation.Loader applies remaining relocation at load address. Verification / Alternative check: Inspect an object file (e.g., with objdump) to view relocation sections created at assembly/compile time; observe how the loader/linker uses them later. Why Other Options Are Wrong: Relocating loader (Option A) consumes relocation bits; it does not generate them.Linker (Option B) may create new relocation records when combining modules, but the original markings originate in the assembler/translator.Macro processor (Option D) simply expands macros before translation; it does not create relocation info. Common Pitfalls: Confusing who generates versus who applies relocation. Assuming absolute loaders never need relocation metadata—hybrid scenarios exist. Final Answer: Assembler or translator.

Question 7

Scheduling Objectives  Which scheduling objective best fits this policy: “Admit jobs to create a mix that will keep most devices (CPU, disks, printers, network) busy”?

Accepted Answer

Introduction / Context: Schedulers aim to meet various objectives: fairness, priority adherence, predictability, throughput, and resource balance. Some workloads saturate one device while leaving others idle; a balanced job mix increases overall system efficiency. Given Data / Assumptions: Heterogeneous jobs with different resource profiles (CPU-bound, I/O-bound). Goal is to keep most subsystems productively engaged. Concept / Approach: Resource balancing admits and sequences jobs so that bottlenecks are minimized and idle times on other resources are reduced. It often increases throughput and improves average response time. Step-by-Step Solution: Classify incoming jobs by dominant resource usage.Adjust admission and dispatching to interleave CPU-bound with I/O-bound jobs.Monitor utilization; revise mix to avoid single-resource saturation. Verification / Alternative check: Utilization metrics (CPU, disk, network) trending closer to target ranges after policy changes confirm improved balance. Queue lengths and response times should reflect reduced contention. Why Other Options Are Wrong: Fairness (Option A) focuses on equitable time, not explicit subsystem balancing.Priority (Option C) enforces importance order, not necessarily balance.Predictability (Option D) emphasizes consistent behavior, not utilization mix. Common Pitfalls: Over-prioritizing one metric (e.g., fairness) at the expense of system throughput. Ignoring changing workload patterns; balancing should be dynamic. Final Answer: To balance resource utilization.

Question 8

Database Fundamentals  Which term refers to the degree to which data in a database are accurate, correct, and consistent over their life cycle?

Accepted Answer

Introduction / Context: Data quality underpins trustworthy analytics and operations. A core concept is data integrity, which encompasses accuracy, consistency, and completeness from creation through storage, transmission, and retrieval. Given Data / Assumptions: Relational databases with constraints, transactions, and auditing. Need to prevent corruption, inconsistency, and unauthorized changes. Concept / Approach: Distinguish integrity from related terms. Security protects against unauthorized access; validity often refers to rule-based correctness at entry; independence separates data from application logic or storage structures. Integrity is the umbrella for accurate, reliable data over time. Step-by-Step Solution: Use constraints (primary/foreign keys, unique, check) to enforce structure.Apply ACID transactions to maintain consistent state despite failures.Audit and backup to detect and recover from anomalies. Verification / Alternative check: Consistency checks, referential integrity validations, and reconciliation reports demonstrate integrity adherence. Violations indicate integrity issues even if access control is strong. Why Other Options Are Wrong: Security (Option A) controls access, not accuracy per se.Validity (Option B) is typically a subset (e.g., format/range checks) at entry time.Independence (Option C) is architectural separation, not data correctness. Common Pitfalls: Assuming security guarantees integrity—insider errors can still corrupt data. Relying solely on application checks without database constraints. Final Answer: Data integrity.

Question 9

Memory Allocation Strategies  In which storage placement strategy is a program placed into the smallest available free hole (partition) in main memory?

Accepted Answer

Introduction / Context: Dynamic memory allocation in operating systems or allocators often uses placement strategies to choose where to place a new block. Best fit, first fit, and worst fit are classic policies with different fragmentation characteristics. Given Data / Assumptions: Variable-sized free memory holes available for allocation. Goal is to select a hole for an incoming request of size S. Concept / Approach: Best fit finds the smallest hole that is still large enough for S, aiming to leave minimal leftover space. First fit uses the first adequate hole encountered. Worst fit chooses the largest hole to reduce the number of small fragments (with mixed results). Buddy systems split memory in powers of two. Step-by-Step Solution: Scan free list for holes >= S.Select the smallest qualifying hole (best fit).Allocate S; if leftover remains, it becomes a smaller free hole. Verification / Alternative check: Simulate allocations and measure external fragmentation. Best fit tends to create many tiny holes, while first fit is faster and may fragment differently. Observations confirm best fit chooses the smallest adequate hole. Why Other Options Are Wrong: First fit (Option B) chooses the first adequate hole, not necessarily the smallest.Worst fit (Option C) deliberately chooses the largest hole.Buddy (Option D) uses power-of-two blocks, not arbitrary smallest holes. Common Pitfalls: Assuming best fit always minimizes fragmentation; it may produce unusable slivers. Ignoring allocation speed differences among strategies. Final Answer: Best fit.

Question 10

Loader Responsibilities  In an absolute loading scheme, which loader-related function is instead accomplished earlier by the assembler (rather than at load time)?

Accepted Answer

Introduction / Context: Loaders vary from absolute loaders (minimal intelligence) to relocating or linking loaders. In an absolute scheme, the assembler resolves addresses to absolute values during assembly, so the loader simply copies code to a predefined location without further fix-ups. Given Data / Assumptions: Single-module, fixed load address scenario typical of absolute loaders. Assembler emits absolute addresses with no relocation entries to process at load time. Concept / Approach: Determine which tasks are handled pre-load. Absolute loaders do not adjust addresses; relocation (reallocation) is already baked into the object by the assembler. Allocation policies and multi-module linking fall outside the absolute loader’s scope in this basic scenario. Step-by-Step Solution: Assemble source with a predetermined origin address.Assembler computes absolute addresses (effectively performing relocation during assembly).Absolute loader transfers bytes to memory at the designated address and begins execution. Verification / Alternative check: Inspect the object listing: lack of relocation records confirms the loader need not adjust addresses. Any change in load location would require re-assembly in a pure absolute scheme. Why Other Options Are Wrong: Allocation (Option B) is an OS memory manager concern, not the assembler’s job.Linking (Option C) is performed by a linkage editor or linking loader, not by the assembler in the absolute loader model.Loading (Option D) is the loader’s essential task, not the assembler’s. Common Pitfalls: Confusing absolute loaders with relocating loaders. Assuming external symbol resolution happens during assembly for multi-module programs—it typically does not in the absolute model. Final Answer: Reallocation (relocation of addresses).

Question 11

Assembler language basics for systems programming: Which statement best describes assembler (assembly) language in relation to the underlying machine language and typical user interfaces?

Accepted Answer

Introduction / Context: Assembly (assembler) language sits just one step above raw machine code. It replaces numeric opcodes and addresses with human-readable mnemonics and labels, enabling low-level control while remaining closer to the hardware than high-level languages. This question checks recognition of assembly’s defining characteristic and contrasts it with unrelated ideas such as user interfaces or formatting rules. Given Data / Assumptions: We compare assembly language to machine language and other concepts. Assembly employs mnemonics (e.g., MOV, ADD, JMP) and symbolic labels. Typical “user interfaces” are shells, GUIs, or CLIs, not assembly. Concept / Approach: Machine language is a stream of binary opcodes and operands. Assembly language is a symbolic representation of that same instruction set, mapping each mnemonic to a specific opcode and allowing labels/macros for readability. An assembler translates the mnemonics and symbols into executable machine code for a particular CPU architecture. Step-by-Step Solution: Identify the essential property: assembly is a symbolic (mnemonic) form of machine instructions.Eliminate distractors: “primary user interface” describes shells/GUI, not assembly.Note formatting: many assemblers are not strictly fixed-format; syntax varies by assembler (AT&T vs Intel, etc.).Therefore, the statement that best defines assembly is “mnemonic form of machine language.” Verification / Alternative check: Any CPU reference (e.g., x86, ARM) shows a one-to-one or close mapping between assembly mnemonics and opcodes, confirming the mnemonic relationship. Why Other Options Are Wrong: Primary user interface: assembly is a programming language, not an interface layer. Requires fixed-format: not universally true; formats differ by toolchain. Quite different from SCL interpreter: vague and not a defining property. None: incorrect because one correct statement exists. Common Pitfalls: Confusing assembly with high-level scripting shells; assuming rigid formatting rules across all assemblers. Final Answer: is a mnemonic form of machine language

Question 12

Operating systems concept: Procedures that can be safely shared by multiple tasks concurrently without modification are called what?

Accepted Answer

Introduction / Context: In multitasking systems, several threads or processes may call the same routine at the same time. Some procedures are designed to be safely invoked concurrently without corrupting state. Knowing the correct term is fundamental for systems, embedded, and real-time programming. Given Data / Assumptions: Multiple callers may enter the same routine simultaneously. No global writable state is assumed inside the routine, or such state is properly protected. Code must not self-modify. Concept / Approach: A reentrant procedure can be paused and safely re-entered by another thread/task because it uses no shared, modifiable global data without protection, does not rely on static non-const state, and keeps all temporary data on the stack or in caller-provided storage. Reentrancy is stricter than mere “thread-safety.” Step-by-Step Solution: Identify the property: safe concurrent use of the same code body.Relate to implementation: no self-modifying code; local automatic storage; immutable code segment.Name the concept: “reentrant procedures.”Reject imprecise alternatives that do not address concurrency correctness. Verification / Alternative check: Classic OS texts define reentrancy for library routines used by interrupts or multiple tasks (e.g., ISR-safe functions must be reentrant). Why Other Options Are Wrong: Serially usable: implies one-at-a-time, not concurrent. Concurrent procedures: vague; does not guarantee safety. Topdown procedures: relates to design style, not concurrency. None: incorrect since “reentrant” is the established term. Common Pitfalls: Equating “thread-safe” with “reentrant” in all cases; relying on hidden globals (e.g., errno-like variables) without protection. Final Answer: reentrant procedures

Question 13

Link-editing workflow in build systems: What is the primary output created by a linker when combining one or more object files and libraries?

Accepted Answer

Introduction / Context: After compilation/assembly, object files contain code and data plus unresolved references. The linker’s job is to resolve references, perform relocation, and emit an image suitable for loading and execution. Understanding this step is essential to diagnosing build and runtime issues. Given Data / Assumptions: Multiple object modules and libraries may be present. Some symbols are defined across different modules. A loader will later place the finished image into memory. Concept / Approach: The linker combines inputs to produce a load module (executable or shared library) with all external references resolved and sections relocated. The loader then maps this module into memory at run time. Compilers alone do not typically emit final, fully linked executables without invoking a linker stage (often invoked under the hood). Step-by-Step Solution: Take object files and libraries as input.Resolve undefined symbols to their definitions.Relocate code/data to final addresses.Emit a load module suitable for the loader. Verification / Alternative check: Toolchains (e.g., ld, LINK) output .exe, .out, .elf, .dll, or .so—canonical load modules. Why Other Options Are Wrong: Not necessary with variable partitions: memory partitioning is unrelated to linking necessity. Must be run after the loader: inverted; the loader runs after linking. Not needed with a good compiler: compilers still rely on linking to combine modules. Common Pitfalls: Confusing compile and link steps; assuming a single-file program skips linking (the toolchain still links standard libraries). Final Answer: creates a load module

Question 14

Core role of an operating system: Among the choices below, what is the primary job of the OS within a computer system?

Accepted Answer

Introduction / Context: The operating system (OS) coordinates hardware and software to enable reliable, efficient program execution. It abstracts complexity and arbitrates limited resources among competing processes. This question focuses on the OS’s central mission. Given Data / Assumptions: Computers have finite CPU, memory, I/O, and storage. Multiple applications may run concurrently. Users and programs require stable interfaces. Concept / Approach: The OS manages resources via scheduling, memory management, device drivers, file systems, and security. While utilities or user-friendliness matter, they are secondary to resource management, which guarantees fairness, isolation, and performance under load. Step-by-Step Solution: Identify OS responsibilities: CPU scheduling, memory allocation, I/O, storage, IPC.Assess options: “manage resources” captures all these domains.Conclude that resource management is the primary job.Select the corresponding answer. Verification / Alternative check: Standard OS definitions emphasize resource management as the core function; UI and utilities are layered atop these mechanisms. Why Other Options Are Wrong: Command resources: vague phrasing, not a standard term. Provide utilities: utilities are tools provided by the OS but are not its fundamental purpose. Be user friendly: desirable but not the OS’s primary technical role. Common Pitfalls: Equating OS with its GUI; ignoring headless servers and embedded OSes where management is primary. Final Answer: manage resources

Question 15

Software engineering practice: Which option best captures the main advantages of modular programming in large software projects?

Accepted Answer

Introduction / Context: Modular programming structures software as a set of cohesive, loosely coupled modules with well-defined interfaces. This approach is foundational for scalability, team collaboration, and long-term maintainability in modern development practices. Given Data / Assumptions: Large codebases benefit from separation of concerns. Teams often work in parallel on different components. Modules expose interfaces and hide implementation details. Concept / Approach: Benefits of modularity include maintainability (localized changes), reusability (modules used across projects), testability (unit tests per module), and parallel development (clear boundaries). It also can improve build times via separate compilation and can yield performance or size gains when modules enable targeted optimizations—though these are not guaranteed in every case. Step-by-Step Solution: Identify core modular benefits: reuse, maintainability, debuggability.Recognize team advantages: parallel work streams and clearer ownership.Note potential secondary gains: faster builds, targeted optimization, improved code quality.Choose the most comprehensive option that lists these advantages together. Verification / Alternative check: Software engineering literature consistently cites modularity as a key to managing complexity (e.g., information hiding, modular design patterns). Why Other Options Are Wrong: Only faster execution / only smaller code: too narrow and not universally true. Reusability and easier maintenance only: partially correct but not as comprehensive as the best choice. None: incorrect because substantial advantages exist. Common Pitfalls: Assuming modularity always improves runtime speed; confusing module boundaries with microservices or over-fragmenting the codebase. Final Answer: All of the above (reusability, easier maintenance, easier debugging, parallel development)

Question 16

Dynamic linking concept: The transfer-vector (jump table) approach primarily enables access to which kind of external element across separately compiled modules?

Accepted Answer

Introduction / Context: Some linkers and operating environments use transfer vectors (jump tables) to insulate call sites from the absolute addresses of external routines. Understanding what is accessed through these vectors clarifies binary compatibility and late binding strategies. Given Data / Assumptions: Modules are compiled separately. Calls to external code may change address across versions. A level of indirection (transfer vector) is used for calls. Concept / Approach: A transfer vector is a table of branch/jump instructions or pointers that redirect calls to the current address of an external subroutine. Callers invoke the stub in the vector rather than a fixed absolute address. This enables updating libraries without recompiling dependents, provided the vector layout remains stable. Access to external data typically uses relocation or import address tables specific to data, not the same jump indirection intended for code calls. Step-by-Step Solution: Identify the purpose: indirecting calls to functions across modules.Map mechanism: call site → transfer vector entry → actual routine.Conclude: primary use is for external subroutines, not general data segments.Select the corresponding option. Verification / Alternative check: Historical systems (e.g., classic UNIX shared libraries, some embedded linkers) and modern import tables use similar indirection for functions. Why Other Options Are Wrong: External data segments / data in other procedures: typically accessed via relocated data pointers or GOT/IAT entries distinct from function jump vectors. All of the above: over-generalizes the transfer vector’s primary purpose. Common Pitfalls: Assuming a single mechanism handles both code and data uniformly; conflating PLT/GOT roles in modern ELF/PE formats. Final Answer: External subroutines

Question 17

IT operations best practice: Is system maintenance necessary once software has been deployed and is running correctly?

Accepted Answer

Introduction / Context: Even high-quality systems require ongoing maintenance to address evolving requirements, security updates, hardware changes, and defect fixes. This question targets the principle that maintenance is integral to the software lifecycle, not an optional afterthought. Given Data / Assumptions: Production systems operate in changing environments. Threat landscapes and dependencies evolve. User needs and regulatory requirements change over time. Concept / Approach: Maintenance includes corrective (bug fixes), adaptive (environment changes), perfective (performance/usability), and preventive (refactoring, security hardening) actions. Regardless of initial quality, systems accumulate technical debt and face external changes that mandate maintenance. Step-by-Step Solution: Assess the realities of operations: patches, OS updates, library upgrades.Acknowledge continuous monitoring and incident response.Conclude that maintenance is universally necessary.Select the option reflecting this necessity. Verification / Alternative check: Industry standards (e.g., ITIL, ISO/IEC 14764) define maintenance as a core phase of the software life cycle. Why Other Options Are Wrong: Not necessary / not required if well written: ignores environmental change and security. Always requires several programs: tool count varies; not a defining truth. Common Pitfalls: Assuming “works now” means “will work forever”; neglecting patch management and monitoring. Final Answer: is necessary on all systems, regardless of how good

Question 18

Virtual memory and paging: Which functions are typically performed by paging software in a virtual-memory operating system?

Accepted Answer

Introduction / Context: Paging underpins virtual memory by mapping virtual addresses used by processes to physical frames in RAM. Understanding paging software clarifies how modern OSes isolate processes, enable memory sharing, and provide each program with a consistent address space view. Given Data / Assumptions: Processes use virtual addresses; the OS and MMU translate to physical addresses. The OS manages page tables, faults, and replacement policies. Security and isolation depend on correct mapping and permissions. Concept / Approach: Paging software is responsible for the access environment (each process’s virtual address space), physical memory management (frame allocation, replacement), and enforcing sharing/protection (read/write/execute permissions, copy-on-write). These functions together enable efficient and safe multitasking. Step-by-Step Solution: Confirm that paging sets up per-process address spaces (access environment).Note that it allocates and tracks physical frames (physical address space management).Recognize page-level permissions enabling sharing and protection.Therefore, all listed functions are performed. Verification / Alternative check: OS textbooks (virtual memory chapters) detail these responsibilities, including page faults, TLB management, and protection bits. Why Other Options Are Wrong: Picking any single function understates paging’s comprehensive role. “None” is clearly incorrect. Common Pitfalls: Confusing paging with segmentation; assuming paging is only swapping to disk (it is broader—address translation and protection as well). Final Answer: All of the above

Question 19

Compiler phases terminology: In the compilation of a PL/I program, which phrase best matches the term “Syntax analysis”?

Accepted Answer

Introduction / Context: Compilers proceed through distinct phases: lexical analysis, syntax analysis, semantic analysis, optimization, and code generation. The question focuses on what happens during syntax analysis (parsing) for a PL/I program, but the principle applies broadly to many languages. Given Data / Assumptions: Input tokens have already been produced by the lexer. We are identifying grammar-conformant structures (expressions, statements). Parsing techniques may use reductions in bottom-up parsing. Concept / Approach: Syntax analysis verifies that the token sequence adheres to the language grammar and builds a parse tree or abstract syntax tree. In bottom-up parsers (e.g., LR), reductions repeatedly replace sequences of tokens/nonterminals with a higher-level nonterminal until the start symbol is reached, recognizing syntactic constructs. Step-by-Step Solution: Assume tokens are ready from lexical analysis.Apply grammar rules to group tokens into constructs (e.g., expressions, statements).Use reductions (bottom-up) or recursive descent (top-down) to build structure.Conclude that syntax analysis corresponds to recognition via reductions. Verification / Alternative check: Compiler texts define parsing as grammar-constrained recognition; reductions are a hallmark of shift-reduce parsers. Why Other Options Are Wrong: Basic elements and uniform symbols: lexical analysis, not syntax. Optional/optimal matrix: unclear and not standard terminology. Macro processor/optimal assembly: relates to macro expansion or later stages. Common Pitfalls: Mixing up lexing and parsing; interpreting “reductions” as optimization (it is a parsing action). Final Answer: recognition of basic syntactic constructs through reductions.

Question 20

Compiler optimizations: Within the compilation of a PL/I program, what does “machine-independent optimization” refer to?

Accepted Answer

Introduction / Context: Optimization in compilers occurs both before and after target-specific decisions are made. Machine-independent (target-agnostic) optimizations operate on the intermediate representation (IR) without relying on particular instruction sets, focusing on program semantics to improve efficiency. Given Data / Assumptions: The compiler has produced an IR after parsing and semantic analysis. We have not yet committed to a specific target CPU's instruction set. Transformations must preserve program meaning. Concept / Approach: Machine-independent optimizations include constant folding, dead-code elimination, common subexpression elimination, copy propagation, strength reduction (algebraic), loop-invariant code motion, and simple loop unrolling. These improve the IR regardless of the final machine. Later, machine-dependent optimizations tune register allocation, instruction scheduling, and addressing modes for a specific architecture. Step-by-Step Solution: Identify the stage: work on IR prior to target selection.List canonical target-agnostic transformations (e.g., CSE, DCE).Recognize that the objective is a more optimal IR, not assembly per se.Select the answer describing optimization independent of the target machine. Verification / Alternative check: Modern compilers (e.g., LLVM, GCC) maintain extensive mid-level, machine-independent optimization passes that apply across architectures. Why Other Options Are Wrong: Reductions / syntactic constructs: parsing, not optimization. Uniform symbols: lexical analysis. Macro processor to produce better assembly: macro expansion is orthogonal and often target-specific. Common Pitfalls: Confusing mid-level IR optimizations with backend (machine-dependent) register allocation and scheduling. Final Answer: creation of more optimal intermediate representation independent of target machine.

Operating Systems Concepts Questions