Question 1

Language levels: The statement “LDA B” is written in which category of computer language?

Accepted Answer

Introduction / Context: Computer languages exist at multiple abstraction layers. Recognizing which layer a specific statement belongs to helps you choose the right tools (assembler, compiler) and understand how code maps onto hardware. Given Data / Assumptions: Statement: “LDA B”. LDA is a classic mnemonic meaning “Load Accumulator,” and “B” is a symbolic operand/register. Concept / Approach: Assembly language uses human-readable mnemonics (like LDA, MOV, ADD) and symbolic operands that translate 1:1 or nearly so into machine instructions. Machine language is numeric opcodes and operands. High-level languages use English-like syntax and abstractions (if, while, functions, types) with no direct 1:1 mapping to opcodes. Step-by-Step Solution: Identify mnemonic pattern: LDA is not a binary opcode; it is a mnemonic.Operand “B” resembles a register symbol, consistent with assembly usage.Therefore the statement is assembly language. Verification / Alternative check: Assembling “LDA B” would produce a specific numeric opcode sequence; compilers for high-level languages would never accept raw mnemonics as valid source. Why Other Options Are Wrong: (a) Machine language is purely numeric (binary/hex). (c) High-level languages do not use processor mnemonics. (d) “All of the above” cannot be true as categories are mutually exclusive. Common Pitfalls: Equating assembly with machine language due to their close relationship; they are distinct representations. Final Answer: Assembly language.

Question 2

Compiler front-end — syntax analysis (parsing): Which function correctly describes the syntax phase of a compiler?

Accepted Answer

Introduction / Context: After lexical analysis produces tokens, the syntax analysis (parser) checks whether token sequences follow the grammar and typically builds an intermediate representation (IR) such as parse trees, abstract syntax trees, or quadruples/matrices. Given Data / Assumptions: A standard compiler with distinct lexical and syntax phases. Intermediate representation is built for later semantic analysis and code generation. Concept / Approach: Parsing uses context-free grammars and parsing algorithms (LL, LR, etc.) to recognize productions. On recognizing a construct, the parser calls semantic actions to construct an IR node or emit intermediate code. Step-by-Step Solution: Start from tokens supplied by the scanner.Apply grammar to validate structure and detect syntax errors.On successful matches, build IR (trees, DAGs, three-address code). Verification / Alternative check: Compiler texts consistently separate tokenization (lexical) from grammar recognition (syntax) and postpone machine code emission to later phases. Why Other Options Are Wrong: (b), (c) belong primarily to lexical/early symbol management. (d) “Parse into basic tokens” is lexical work, not syntax. (e) Final machine code is a back-end responsibility. Common Pitfalls: Mixing scanning and parsing tasks; assuming direct code generation during parsing. Final Answer: Recognize major language constructs and invoke actions to build an intermediate representation.

Question 3

Machine code to assembly (assumed mapping): Decode the single-byte opcode 0x48 into its assembly instruction (assume it was not produced by a pseudo-op).

Accepted Answer

Introduction / Context: Reverse-assembling a machine opcode requires knowledge of the ISA’s opcode map. Single-byte opcodes typically encode accumulator/register operations or short addressing forms, whereas instructions with immediate or direct addresses need extra operand bytes. Given Data / Assumptions: Opcode: 0x48. No additional operand bytes were provided, implying a single-byte instruction. We assume a conventional accumulator architecture where shifts/rotates and register ops can be single-byte. Concept / Approach: If the instruction consumed only one byte, it cannot encode the multi-byte immediates or addresses visible in options (b), (c), (d). Therefore, a unary accumulator operation such as ASRA (arithmetic shift right accumulator) is the consistent choice. Step-by-Step Solution: Check each option’s operand length.Options with h#.... operands require additional bytes and contradict the single 0x48 byte.Select the operand-less accumulator operation as the plausible decoding. Verification / Alternative check: Consulting the ISA manual would definitively map 0x48 to its mnemonic. In many classic ISAs, 0x48 corresponds to single-byte register/shift ops, aligning with ASRA over memory-addressing forms. Why Other Options Are Wrong: (b), (c), (d) each imply at least two additional operand bytes; they cannot be encoded by a lone 0x48. (e) likewise suggests addressing. Common Pitfalls: Ignoring instruction length; assuming any mnemonic can match without checking required operands. Final Answer: ASRA.

Question 4

Systems software — loader types: Loaders that allow a program to be relocated at load time are called what?

Accepted Answer

Introduction / Context: Loaders place compiled code into memory for execution. When the final memory address is unknown until load time, relocation support is required so that address-sensitive instructions are adjusted appropriately. Given Data / Assumptions: Programs may be loaded at varying base addresses. Relocation records or relocation bits accompany object code. Concept / Approach: Terminology varies across literature. A loader that processes relocation information to adjust addresses at load time is called a “relocating loader” and also commonly a “relative loader,” emphasizing addresses relative to a load base. Step-by-Step Solution: Identify key capability: adjust address-dependent code and data.Match terms used for such loaders: relocating/relative.Conclude both names describe the same capability. Verification / Alternative check: OS and linker/loader texts describe relocation entries processed by relocating loaders. Absolute loaders lack this step. Why Other Options Are Wrong: (d) Absolute loaders place code at a fixed, predetermined address and do not relocate. (e) Static binders are linkers that resolve symbols but may still rely on relocation at load time. Common Pitfalls: Confusing linking with loading; assuming “absolute” can relocate. Final Answer: both (a) and (b).

Question 5

Module properties — safe multi-instance execution: In which type of module can multiple executions overlap in time and still produce the same correct result?

Accepted Answer

Introduction / Context: Systems programming often requires routines that can be invoked concurrently (e.g., by interrupts or multiple tasks). Such routines must be designed to be safely reentered without corrupting state. Given Data / Assumptions: “Multiple instances of execution” may interleave or overlap. Correctness must be preserved regardless of overlapping calls. Concept / Approach: A reenterable (reentrant) module contains no hidden writable shared state, or protects it appropriately. Its code is pure (read-only), and any writable data is on per-invocation stacks or passed explicitly, allowing simultaneous execution by different callers without interference. Step-by-Step Solution: Identify need: safe overlapping calls.Match term: “reenterable module” is specifically defined for this property.Eliminate alternatives: “serially reusable” requires one-at-a-time execution. Verification / Alternative check: Operating systems specify reentrancy for interrupt service routines and library functions, ensuring safety under concurrency. Why Other Options Are Wrong: (a) Non-reusable cannot be safely reused. (b) Serially reusable forbids overlap. (d) Recursive is about self-calls depth, not safe concurrency. (e) Interrupt-driven describes invocation mechanism, not concurrency safety. Common Pitfalls: Confusing recursion with reentrancy; they are independent concepts. Final Answer: reenterable module.

Question 6

Loader functions in absolute loading schemes: In an absolute loader, which function is actually performed by the loader?

Accepted Answer

Introduction / Context: Different loader designs provide different services. An absolute loader is the simplest: it takes object code with fixed, absolute addresses and transfers it into memory for execution without performing relocation or linking. Given Data / Assumptions: Input object code already contains absolute addresses. All external references have been resolved previously (e.g., by the assembler or a separate linker). Concept / Approach: Because addresses are absolute, the loader does not adjust them. It merely reads, verifies, and writes code and data to the specified locations and then starts execution at the given entry point. Step-by-Step Solution: Examine capabilities: no relocation records are processed.No symbol resolution across modules occurs at load time.The loader’s task is to load bytes into memory at the addresses already specified. Verification / Alternative check: OS and systems programming texts separate absolute loaders from relocating loaders and linkers. Only loading is performed in the absolute scheme. Why Other Options Are Wrong: (a) Reallocation/relocation is not done by an absolute loader. (b) Allocation in the sense of dynamic placement is outside its scope. (c) Linking belongs to linkers. (e) Dynamic relocation/binding is a feature of more advanced loaders. Common Pitfalls: Assuming every loader links and relocates; absolute loaders are intentionally minimal. Final Answer: Loading (placing object code into specified memory addresses).

Question 7

In systems software, what is a loader? Choose the most accurate definition that explains its role in placing a program into memory and preparing it for execution.

Accepted Answer

Introduction / Context: A loader is a foundational systems software component that makes an executable program ready to run. After code has been translated by assemblers or compilers and linked by a linker, the loader takes over to map program segments into memory, resolve any remaining addresses, and transfer control to the program’s entry point. Given Data / Assumptions: The program has already been assembled/compiled and linked into an executable format. The operating system provides memory management services (relocation, protection). The loader is responsible for preparing runtime images and initiating execution. Concept / Approach: Distinguish among build-time tools (compiler, assembler, linker) and run-time preparation tools (loader). The loader performs relocation (adjusting addresses), symbol resolution where required (dynamic linking), allocation of memory for code, data, and stack/heap, and finally jumps to the start routine (entry point). Step-by-Step Solution: 1) Input: an executable image produced by a linker (static or with dynamic dependencies).2) Allocate memory regions for text (code), data, BSS, heap, and stack.3) Perform relocation: adjust absolute and relative addresses based on load address.4) Resolve dynamic libraries if needed and patch procedure linkage tables.5) Initialize the program environment and transfer control to the program entry point. Verification / Alternative check: Observe program launch on any modern OS: the executable is mapped into memory (often via demand paging), relocations are applied, and control passes to the runtime startup code, confirming the loader’s responsibilities. Why Other Options Are Wrong: Assemblers (option b) translate assembly to machine code. Interpreters (option c) execute source or bytecode directly without producing a native executable. Compilers (option d) translate high-level language into object code; they do not place programs into memory for execution. Editing comments (option e) is unrelated to loading. Common Pitfalls: Confusing the linker with the loader; the linker prepares the image, while the loader maps and starts it. Also, assuming the loader only copies bytes—modern loaders also handle dynamic linking and relocations. Final Answer: a program that places programs into memory and prepares them for execution

Question 8

In compiler construction, which table made during lexical analysis lists every literal used in the source program?

Accepted Answer

Introduction / Context: Lexical analysis (the scanner phase) reads raw source text and converts it into a stream of tokens. During this process, the compiler builds auxiliary tables to manage tokens efficiently. Understanding which table stores which kind of lexical item is essential for both compiler design and language tooling. Given Data / Assumptions: Literals are constant values written directly in code (e.g., numbers, character constants, string constants). Identifiers name variables, functions, classes, etc. The lexer populates symbol-like tables to enable fast lookup and to avoid duplication. Concept / Approach: The literal table records each literal encountered (with attributes such as type, length, and value). The identifier table (or symbol table) holds names and their scope/linkage attributes. Parser structures like productions and reductions belong to syntax analysis, not lexical analysis. Step-by-Step Solution: 1) Classify tokens: identifiers vs. literals vs. keywords/operators.2) Associate storage: literals are stored in a literal table; identifiers go to a symbol/identifier table.3) Exclude parsing artifacts: reductions/productions are grammar-level, not lexical tables.4) Select the correct table for literals: the literal table. Verification / Alternative check: Many compiler textbooks and tools (e.g., classic one-pass or two-pass compilers) separate pools for literals (string pool) and symbols, confirming the role of the literal table. Why Other Options Are Wrong: Terminal table (option a) is a grammar concept listing terminal symbols. Identifier table (option c) stores names, not constants. Reductions (option d) occur in parsing actions, not lexical storage. Production table (option e) describes grammar rules. Common Pitfalls: Confusing string literals with identifiers because both are alphanumeric; literals are values, identifiers are names. Final Answer: Literal table

Question 9

Assembly language pseudo-op conversion: interpret “.BYTE h#F8” and give the resulting machine byte in hexadecimal.

Accepted Answer

Introduction / Context: Assemblers support pseudo-operations (pseudo-ops) that direct data placement without generating CPU opcodes. The “.BYTE” directive reserves one byte and initializes it with a specified value. Understanding numeric bases in assembler syntax is crucial for correct binary images. Given Data / Assumptions: “.BYTE” places a single 8-bit value into the object. “h#F8” denotes a hexadecimal constant F8. No endianness issue arises for a single byte. Concept / Approach: Translate the constant exactly as written. Hexadecimal F8 corresponds to decimal 248 and binary 11111000. The assembler emits this one byte into the output at the current location counter. Step-by-Step Solution: 1) Recognize directive: “.BYTE” → allocate 1 byte.2) Read constant: “h#F8” → hexadecimal F8.3) Emit value: the generated machine data is 0xF8.4) Present in hex form as required: “F8”. Verification / Alternative check: Convert F8 hex to decimal: 15*16 + 8 = 248. In binary: 11111000 (8 bits), matching a single byte size. Why Other Options Are Wrong: “0111EF” and “F8 16” are malformed or multi-byte sequences. “03 16” represents two bytes. “42 65 61 72” are ASCII for “Bear,” unrelated to the directive. Common Pitfalls: Confusing directives that emit multiple bytes (e.g., .WORD) with .BYTE, or misreading the base prefix leading to an incorrect numeric value. Final Answer: F8

Question 10

Interpreters: identify the statement that is NOT true about how an interpreter operates compared with a compiler.

Accepted Answer

Introduction / Context: Programming language implementation involves compilers and interpreters. While both are translators at some level, they differ in when and how they produce executable artifacts. Recognizing these differences helps developers understand performance, deployment, and tooling choices. Given Data / Assumptions: Compilers translate source into object/executable files before execution. Interpreters analyze and execute source (or bytecode) directly at run time. Some systems use hybrids (JIT compilation), but the classic distinction still applies. Concept / Approach: The key discriminator: compilers emit object code; interpreters typically do not generate a permanent object module. Instead, interpreters repeatedly parse or execute intermediate forms for each run, often line by line or statement by statement, possibly with caching. Step-by-Step Solution: 1) Identify what is being asked: pick the statement that is NOT true of interpreters.2) Option a claims interpreters generate object programs—this describes compilers, not interpreters.3) Option b is correct: an interpreter is a translator (source → actions/bytecode execution).4) Option c is correct in spirit: interpreters analyze statements at execution time.5) Option e is also correct: interpreters execute without standalone binaries. Verification / Alternative check: Common interpreted environments (Python, Ruby, many shells) execute code directly or via bytecode VMs, without producing separate object files for the user. Why Other Options Are Wrong: Options b, c, and e accurately capture interpreter behavior. Option d (“All of the above”) is incorrect because option a is false. Common Pitfalls: Overgeneralizing JIT compilers as interpreters or vice versa; hybrids still retain the fundamental idea that classic interpreters do not emit object modules like compilers. Final Answer: Interpreter generates an object program from the source program

Question 11

Software quality terminology: in programming practice, what does the term “bug” mean?

Accepted Answer

Introduction / Context: The word “bug” is widely used in software engineering to mean a flaw that causes incorrect behavior. Understanding the difference between types of errors (syntax, semantic, logical, runtime) helps teams triage issues and improve software reliability. Given Data / Assumptions: “Bug” is general slang for a defect; contextually, most usage points to logic or behavioral errors. Syntax errors are typically caught by compilers or linters before execution. Documentation activities are not bugs. Concept / Approach: A logical error causes a program to run but produce wrong results because the algorithm or control flow is flawed. This differentiates it from syntax errors (violations of language grammar) and from intentional actions like documentation or optimization. Step-by-Step Solution: 1) Evaluate each option against standard definitions.2) Option a matches the common meaning: a programming defect that breaks logic or expected behavior.3) Option b is too narrow; syntax errors are compiler-detected and not typically called “bugs.”4) Option c is unrelated to defects.5) Option d cannot be correct because c is not a bug. Verification / Alternative check: Issue trackers categorize bugs as defects, separate from tasks like “documentation” or “enhancement,” and from “build errors” caused by syntax issues. Why Other Options Are Wrong: Syntax errors stop compilation (option b) and are usually not labeled runtime “bugs.” Documentation (option c) is a process, not a defect. “All of the above” (option d) fails because c is invalid. Common Pitfalls: Equating any compiler diagnostic with a bug, or calling request-for-change items “bugs.” Bugs refer to defects in functionality or reliability. Final Answer: A logical error in a program

Question 12

What is a base register table in systems programming? Select the description that best matches its purpose during assembly and linking.

Accepted Answer

Introduction / Context: On architectures that support base-displacement addressing, a base register table helps assemblers, linkers, and loaders track which registers hold base addresses and what those addresses are. This facilitates correct code generation and relocation. Given Data / Assumptions: Target architecture supports using general-purpose registers as base registers. Assembler or relocation process must know current base assignments. Programs may switch base registers for different segments or modules. Concept / Approach: A base register table maintains mappings from register identifiers to base addresses. During code generation and relocation, effective addresses are formed as base + displacement. The table ensures correctness when registers are repurposed or when code is moved (relocated) to a different memory region. Step-by-Step Solution: 1) Identify need: efficient addressing through base + displacement.2) Track which registers currently serve as base registers.3) Record the base address for each such register.4) Use this table during assembly/relocation to compute correct effective addresses. Verification / Alternative check: Examine assembler listings: base register usage and associated displacement calculations typically reference an internal structure equivalent to a base register table, confirming the role described. Why Other Options Are Wrong: Option a is too generic. Option c describes multiprogramming, not the table’s function. Option d is about source notation, not the internal table. Option e concerns memory management algorithms, unrelated to base registers. Common Pitfalls: Confusing base register tables with page tables or segment descriptors; the former is an assembler/relocation aid, not an OS-level memory mapping structure. Final Answer: a structure used to remember which general-purpose registers are available as base registers and what base addresses they contain

Question 13

What is a compiler? Choose the definition that correctly describes its input and output in the software toolchain.

Accepted Answer

Introduction / Context: In the build pipeline, the compiler translates human-readable high-level language (HLL) into lower-level representations, typically object code, that can be linked and then executed. Understanding this role clarifies how compilers differ from assemblers, interpreters, linkers, and loaders. Given Data / Assumptions: Source language: high-level (e.g., C, C++, Java to bytecode, etc.). Output: object files or intermediate representations suitable for linking. Separate tools may handle linking and loading. Concept / Approach: A compiler performs lexical, syntax, and semantic analysis, then optimization and code generation. The result is an object module or executable form (possibly with relocations) that a linker and loader will further process. Step-by-Step Solution: 1) Parse HLL source into an abstract syntax tree.2) Perform semantic checks and intermediate code generation.3) Optimize and generate target object code.4) Emit object program for the linker. Verification / Alternative check: Build systems show .c → .o via compiler invocations, then linking to form executables or libraries, validating the definition. Why Other Options Are Wrong: Option a is the loader. Option b is the assembler. Option d describes an interpreter. Option e is not part of the compilation process. Common Pitfalls: Assuming the compiler also links and loads; while integrated toolchains exist, conceptually these are distinct stages. Final Answer: program that accepts a program written in a high-level language and produces an object program

Question 14

Macro processors for assembly language: which implementation approaches are possible?

Accepted Answer

Introduction / Context: Macro facilities expand programmer productivity by allowing parameterized text substitution and code generation. Macro processors can be implemented in several ways, and understanding these approaches helps in appreciating assembler design and build performance. Given Data / Assumptions: Macros are expanded before or during assembly to produce final source for the assembler proper. Assemblers may be one-pass or two-pass. Macro expansion can be a separate preprocessing step or integrated. Concept / Approach: An independent macro processor (one-pass or two-pass) runs before the assembler, outputting expanded code. Alternatively, macro processing can be integrated inside one of the assembler passes, reducing I/O and preserving symbol information more tightly. Step-by-Step Solution: 1) Identify macro roles: parameter substitution, conditional expansion, repetition.2) Consider pipeline placement: pre-assembler (independent) vs. within assembler.3) Recognize that both one-pass and two-pass macro processors exist.4) Conclude that all listed implementation approaches are valid. Verification / Alternative check: Historical assemblers and modern toolchains document macro preprocessors as separate tools or as integrated phases, confirming the multiple viable strategies. Why Other Options Are Wrong: Options a, b, and c are each correct on their own, so “None of these approaches” is false. Therefore “All of the above” is the correct comprehensive choice. Common Pitfalls: Assuming macros must always be a separate preprocessor; many assemblers integrate macro expansion to support symbol scoping and listing alignment. Final Answer: All of the above

Question 15

Algorithm concept: choose the best description of an algorithm in computing and problem solving.

Accepted Answer

Introduction / Context: An algorithm is the backbone of computing—an explicit, finite sequence of steps that transforms input into output. Recognizing what an algorithm is (and is not) helps distinguish coding syntax from problem-solving methodology. Given Data / Assumptions: An algorithm describes logic, not programming language syntax. It must be precise, finite, and effective. It is independent of any particular hardware or language. Concept / Approach: The defining attributes of an algorithm include definiteness (each step is unambiguous), finiteness (terminates), and effectiveness (each step is basic enough to be executed). These criteria separate algorithms from vague heuristics and from descriptive prose. Step-by-Step Solution: 1) Evaluate option texts against algorithm attributes.2) Option b matches: a finite, ordered sequence of steps to solve a problem.3) Options a and c misclassify the concept as a language or a math branch.4) Therefore, choose option b as the most accurate description. Verification / Alternative check: Classic examples—Euclid’s algorithm for GCD, sorting algorithms—exemplify stepwise procedures independent of any programming language. Why Other Options Are Wrong: Option a: a language is a notation for expressing algorithms, not the algorithm itself. Option c: algorithms are used in mathematics but are not a branch of it. Option d cannot be true because a and c are incorrect. Option e contradicts the definitive nature of algorithms. Common Pitfalls: Equating pseudocode or code with the algorithm; the algorithm is the logic, while code is one expression of it. Final Answer: A step by step procedure for solving a problem

Question 16

Front-end phases: the action of organizing source tokens into syntactic structures (statements, expressions) is called what?

Accepted Answer

Introduction / Context: Compilers and interpreters transform source code through a pipeline of phases. After lexical analysis converts characters into tokens, parsing (syntax analysis) builds structured representations such as parse trees or abstract syntax trees that reflect the grammar of the language. Given Data / Assumptions: Source code is available as a sequence of tokens from the lexer. A formal grammar (often context-free) defines valid sentence structures. The parser checks conformance and reports syntax errors. Concept / Approach: Syntax analysis applies parsing algorithms (LL, LR, LALR, recursive descent, etc.) to group tokens into syntactic classes—expressions, statements, declarations—according to grammar rules. This yields a tree structure used by later semantic analysis and code generation. Step-by-Step Solution: 1) Lexer produces tokens: identifiers, literals, operators, keywords.2) Parser consumes tokens and applies production rules.3) If tokens match grammar patterns, build parse/AST nodes.4) On mismatch, report syntax errors with locations and expectations. Verification / Alternative check: In typical compiler outputs (e.g., debug flags), you can visualize parse trees or see parser states and reductions, confirming the role of syntax analysis. Why Other Options Are Wrong: Lexical analysis (option b) is tokenization, not parsing. “Interpretation analysis” (option c) is not a standard phase name. “General syntax analysis” (option d) is vague. “Token coloring” (option e) refers to editor highlighting, not compilation. Common Pitfalls: Confusing semantic analysis (types, scope) with syntax analysis; semantics happens after parsing on the structured representation. Final Answer: syntax analysis

Language Processors Questions