Question 1

Bus directionality fundamentals Which bus in a conventional microprocessor system is inherently bidirectional for transfers between the CPU and devices?

Accepted Answer

Introduction / Context: Understanding which buses are uni- versus bidirectional is foundational to tracing data flow on schematics and timing diagrams. This knowledge informs buffer selection and signal integrity considerations. Given Data / Assumptions: The system has separate address, data, and control buses. CPU reads and writes to memory and I/O devices. No specialized bus multiplexing or serial bus overlays are assumed. Concept / Approach: The address bus carries location information from CPU to devices and is therefore unidirectional. The data bus must carry information in both directions (CPU writes data out and reads data back), making it bidirectional. Control lines have defined directions; some originate at the CPU (read/write strobes), others originate at devices (interrupts), but each line itself is not bidirectional. Step-by-Step Solution: Identify bus roles.Address: CPU → devices only.Data: CPU ↔ devices → must be bidirectional.Control: mixed origin per signal; not a single bidirectional bus. Verification / Alternative check: Inspection of CPU datasheets shows separate drivers/receivers on data pins (often configured as tri-state) compared with output-only address pins. Why Other Options Are Wrong: Address bus: typically one-way from CPU. Control bus: per-signal direction set, not “bidirectional as a bus.” None: incorrect because the data bus is bidirectional. Common Pitfalls: Confusing “shared backplane” with “bidirectional per line.” Data lines are tri-stated and arbitrated; address lines are driven by one master in most basic systems. Final Answer: Data bus

Question 2

8086/8088 architectural advances over 8085 Which of the following was NOT a specific design improvement attributed to the 8086/8088 family when compared to the earlier 8085?

Accepted Answer

Introduction / Context: The 8086/8088 introduced a significant internal reorganization compared to the 8085, including pipelined fetching and wider word operations. Distinguishing new features from generic CPU blocks clarifies learning about x86's historical evolution. Given Data / Assumptions: 8086/8088 added a Bus Interface Unit (BIU) and an Execution Unit (EU) split to support instruction prefetch and simple pipelining. 8086 implemented 16-bit internal processing and (for 8086) a 16-bit external data bus; 8088 retained an 8-bit external data bus. An arithmetic logic unit (ALU) exists in virtually all CPUs, including 8085. Concept / Approach: We are to select the option that does not represent a distinctive improvement of the 8086/8088 over the 8085. While EU, BIU, and the 16-bit external bus (on 8086) were hallmark advances, the ALU is a basic CPU component present in both generations. Step-by-Step Solution: List innovations → EU, BIU, wider word/bus support.Recognize ALU as not unique to 8086/8088.Therefore, “Arithmetic logic unit (ALU)” is not the differentiator. Verification / Alternative check: Architectural block diagrams of 8085 vs. 8086 show the EU/BIU split and prefetch queue as 8086 family additions; both families have an ALU. Why Other Options Are Wrong: Execution unit: new partitioning element. 16-bit data bus: external 16-bit bus for 8086; broader 16-bit processing. Bus interface unit: dedicated fetch/bus module absent in 8085. Common Pitfalls: Assuming “ALU” is synonymous with advanced capability; it is common to all general CPUs. Final Answer: Arithmetic logic unit (ALU)

Question 3

Identify non-bus terminology Which of the following options is NOT a recognized system bus category in standard computer architecture?

Accepted Answer

Introduction / Context: System buses provide structured pathways for communication in computers and embedded systems. The canonical trio is address, data, and control. Recognizing valid terminology prevents confusion when reading block diagrams and datasheets. Given Data / Assumptions: Typical systems expose address, data, and control buses. Timers are peripherals that may connect to buses but are not buses themselves. Concept / Approach: We are to select the item that is not a bus category. “Timer bus” is not standard nomenclature; timers attach to buses or internal interconnects but do not define a separate bus class in the basic taxonomy. Step-by-Step Solution: List standard buses → address, data, control.Compare options → “Timer bus” stands out as nonstandard.Choose → Timer bus is not a bus category. Verification / Alternative check: Introductory architecture texts and microcontroller references consistently describe the three-bus model without mentioning a distinct “timer bus.” Why Other Options Are Wrong: Data, control, and address buses are fundamental and universally referenced. Common Pitfalls: Assuming that because a subsystem (timer) interacts with a bus, it defines a new bus category. Final Answer: Timer bus

Question 4

Bus access conflicts In a shared bus system, what condition arises when two or more sources attempt to drive the same bus lines at the same time?

Accepted Answer

Introduction / Context: Shared buses require arbitration to prevent multiple drivers from asserting conflicting logic levels simultaneously. When arbitration fails or is absent, electrical conflict occurs, risking data corruption and hardware damage. Given Data / Assumptions: Multiple potential bus masters or devices can drive the bus. Tri-state buffers or open-collector/open-drain schemes are used to allow sharing. Arbitration/enable control should ensure only one active driver at a time. Concept / Approach: “Bus contention” describes the event where more than one driver actively drives the bus. This can cause excessive currents (e.g., one device drives HIGH, another drives LOW), noise, and logic errors. Step-by-Step Solution: Identify conflict scenario → simultaneous drivers.Name the condition → bus contention.Relate mitigations → arbitration logic, proper enable timing, pull-ups for open-collector. Verification / Alternative check: Hardware debug often reveals contention by observing abnormal current draw and distorted waveforms; logic analyzers show overlapping drive windows. Why Other Options Are Wrong: Direct memory access: a controlled transfer method, not a fault. Bus interruption: vague; not the standard term. PPI: stands for programmable peripheral interface, unrelated to the fault. Common Pitfalls: Forgetting to tri-state outputs during reset or handover; incorrect chip-enable timing. Final Answer: Bus contention

Question 5

DMA suitability — choosing endpoints Direct Memory Access (DMA) is particularly well-suited for high-throughput transfers between which pair of system components?

Accepted Answer

Introduction / Context: DMA offloads block data transfers from the CPU by allowing a controller to move data directly between peripherals and memory. This boosts throughput and frees CPU cycles for computation rather than byte-by-byte copying. Given Data / Assumptions: Typical system includes mass storage (disk), RAM, and a DMA controller. Goal: rapid, large transfers with minimal CPU intervention. Concept / Approach: DMA is most beneficial when a peripheral must move large data blocks into or out of main memory. Storage devices (like disks) commonly use DMA to stream sectors to RAM buffers. The CPU sets up the transfer descriptors and is interrupted upon completion. Step-by-Step Solution: Identify high-volume path → disk ↔ RAM.DMA controller arbitrates bus, performs bursts.CPU overhead minimized → improved system performance. Verification / Alternative check: Operating systems and drivers routinely configure DMA for disk, network, and multimedia devices to move data to/from RAM without CPU copying. Why Other Options Are Wrong: Disk ↔ CPU: defeats DMA’s purpose; CPU would be in the data path. Disk ↔ ROM: ROM is not a standard destination for runtime data streams. Disk ↔ I/O: vague; ultimate destination for bulk data is usually RAM for processing. Common Pitfalls: Ignoring cache coherency or alignment in DMA buffers; mishandling memory protection when mapping DMA regions. Final Answer: disk drive and RAM

Question 6

8086/8088 segment registers — identify the invalid name Which of the following is NOT a valid segment register name in the 8086/8088 architecture?

Accepted Answer

Introduction / Context: The 8086/8088 memory model is built around segment:offset addressing with distinct segment registers. Recognizing correct register names helps in reading assembly and understanding how memory is partitioned. Given Data / Assumptions: 8086/8088 segment registers include CS, DS, SS, and ES (extra segment). No register named “AS” exists. Concept / Approach: By comparing the offered names with the canonical set, we can quickly identify the imposter. “Address segment (AS)” is not part of the x86 register file. Step-by-Step Solution: List actual segment registers → CS, DS, SS, ES.Scan options → CS, DS, SS are valid; “AS” is unknown.Select the invalid name → Address segment (AS). Verification / Alternative check: Any 8086/8088 programming reference confirms the four segment registers above; later x86 added FS and GS, still no “AS.” Why Other Options Are Wrong: CS, DS, SS are all standard and essential to 8086/8088 operation. Common Pitfalls: Confusing “address” as a generic term with a specific register name; “address” is a function, not a register label. Final Answer: Address segment (AS)

Question 7

First Intel microprocessor with on-chip cache Identify the first Intel x86 microprocessor that integrated cache memory directly on the CPU die.

Accepted Answer

Introduction / Context: On-chip cache dramatically reduced average memory access latency and enabled higher instruction throughput. Knowing when cache first appeared on x86 clarifies the performance leaps in successive generations. Given Data / Assumptions: 80386 introduced 32-bit architecture but did not integrate an on-die cache. 80486 integrated an on-chip unified cache and an on-chip FPU (in 486DX). Pentium and later generations expanded cache sizes and levels. Concept / Approach: Chronologically, the 80486 was the first x86 to include an on-chip cache (commonly 8 KB unified). This significantly improved performance even at similar clock speeds compared to the 80386. Step-by-Step Solution: Evaluate timeline → 80386 (no on-die cache).Next generation → 80486 (adds on-chip cache, pipe improvements).Therefore → 80486 is the correct answer. Verification / Alternative check: Historical processor datasheets and architecture summaries consistently attribute on-chip cache introduction to the 80486 family. Why Other Options Are Wrong: 80386: cacheless on die. Pentium/Pentium Pro: later families with larger, more complex cache hierarchies, but not the first. Common Pitfalls: Assuming Pentium first introduced all modern features; many started with 80486. Final Answer: 80486

Question 8

Microprocessor architecture — which item is NOT part of the Execution Unit (EU)? Consider the classic 8086/IA-32 block organization where the Execution Unit (EU) is distinct from the Bus Interface Unit (BIU). Identify the component that does not bel…

Accepted Answer

Introduction / Context: The internal organization of many x86-family processors (for example, 8086 and successors conceptually) distinguishes between the Execution Unit (EU) and the Bus Interface Unit (BIU). Knowing what lives inside the EU helps learners reason about instruction execution, flag updates, and where data is temporarily stored during arithmetic and logic operations. Given Data / Assumptions: The EU is responsible for arithmetic/logic operations and flag updates. The EU typically contains general purpose registers, ALU, instruction decoder, and the flags register. The system clock is a chip-level timing source, not logically part of the EU block. Concept / Approach: The EU performs computations using the ALU and reads/writes the general registers. Status information is recorded in the flags register after operations such as add, sub, inc, dec, cmp, and logical instructions. The clock is a global timing reference that drives the entire CPU and peripheral interfaces; it is not categorized as an EU sub-block. Step-by-Step Solution: List typical EU elements: ALU, general registers, flags, instruction decoder/control for micro-operations.Recognize that the clock signal distributes timing edges across units but is not an EU module.Eliminate EU members from the options and select the remaining non-EU item.Therefore, the correct choice is the clock. Verification / Alternative check: Block diagrams in standard texts show the EU and BIU as separate blocks. The EU contains ALU, registers, and flags; the BIU handles instruction queueing and bus cycles. The system clock lies outside these logical partitions. Why Other Options Are Wrong: Arithmetic logic unit (ALU) is core to the EU. General registers reside inside the EU for fast operand access. Flags are updated by EU operations and are part of the EU. Common Pitfalls: Assuming any resource on the chip is part of the EU. Architecture diagrams separate logical function blocks from global resources like the clock. Final Answer: Clock

Question 9

Microprocessor basics — which item is NOT a fundamental internal element? Select the option that does not describe a core building block commonly found inside a microprocessor.

Accepted Answer

Introduction / Context: A microprocessor is built from several fundamental blocks that cooperate to fetch, decode, and execute instructions. Understanding which blocks are intrinsic clarifies how instructions transform into actions and how data moves internally. Given Data / Assumptions: The typical internal blocks are the ALU, a set of registers (register file), and a control unit that sequences operations. A microcontroller is a system level device that integrates a CPU core plus memory and peripherals on a single chip. The question asks for the choice that is not a basic internal element of a microprocessor. Concept / Approach: The ALU performs math and logic, the register array stores operands and results, and the control unit orchestrates timing and control signals. A microcontroller encompasses an entire embedded system chip and is not a sub-block inside a microprocessor core. Therefore it does not fit as a basic element within a microprocessor. Step-by-Step Solution: Identify core blocks: ALU, registers, control unit.Compare with the term microcontroller, which denotes a complete chip integrating CPU, memory, and I/O.Conclude that microcontroller is not an internal block of a microprocessor. Verification / Alternative check: Consult block diagrams in textbooks: microprocessor cores consistently show ALU, control, and registers as internal; microcontroller appears as a different chip class (MCU) that embeds a microprocessor core. Why Other Options Are Wrong: ALU, register array, and control unit are standard internal elements and indispensable for instruction execution. Common Pitfalls: Confusing microprocessor (CPU core) with microcontroller (CPU plus memory and peripherals). The names are related but denote different integration levels. Final Answer: Microcontroller

Question 10

Instruction set categorization — which one is NOT an arithmetic instruction? Consider common assembly mnemonics used on microprocessors. Identify the instruction that is not arithmetic in nature.

Accepted Answer

Introduction / Context: Classifying instructions by function helps predict effects on flags, register contents, and performance. Arithmetic instructions change numeric values, while rotate/shift operations manipulate bit positions without performing addition or subtraction. Given Data / Assumptions: INC increments an operand by one. DEC decrements an operand by one. CMP performs a subtraction to set flags (no stored result), often considered arithmetic/compare. ROL rotates bits through the carry or within the word, depending on architecture. Concept / Approach: Arithmetic instructions like INC, DEC, ADD, SUB, and CMP act on numeric magnitude and modify arithmetic flags. ROL is a rotate operation (bit manipulation) and is categorized under shift/rotate, not arithmetic, even though it may affect flags such as carry or overflow depending on the CPU. Step-by-Step Solution: Recognize that INC and DEC directly change the operand value.CMP computes a subtraction internally to update flags.Identify ROL as a rotate-left bit manipulation instruction.Therefore, select ROL as not arithmetic. Verification / Alternative check: Review architecture manuals (x86, ARM, 8051): rotate and shift opcodes are grouped separately from arithmetic/logic classes. Why Other Options Are Wrong: INC, DEC, and CMP are treated as arithmetic or arithmetic-related flag-setting operations in most ISAs. Common Pitfalls: Assuming CMP is purely logical because it does not store a result. It still performs an arithmetic subtraction to set flags. Final Answer: ROL (rotate left)

Question 11

Operands in assembly programming — which item below is NOT an operand? Select the option that does not represent a valid operand source or destination in typical assembly language.

Accepted Answer

Introduction / Context: An operand is a value or storage location on which an instruction operates. Understanding what qualifies as an operand clarifies addressing modes and how the CPU fetches data for instruction execution. Given Data / Assumptions: Operands may be immediate values, registers, or memory locations (variables, labels, or addresses). The assembler is a software tool that translates assembly into machine code; it is not part of runtime operands. We consider general assembly conventions, not a specific architecture quirk. Concept / Approach: Registers and memory locations are concrete places where data resides at run time. Variables in assembly map to memory addresses or constants and serve as operands. The assembler operates at build time to convert mnemonics to opcodes; it does not serve as an operand in any instruction at run time. Step-by-Step Solution: List valid operand forms: immediate, register, memory.Recognize that a variable is a label abstraction for a memory location (thus a valid operand).Note that the assembler is a tool, not a run-time entity.Therefore select Assembler as not an operand. Verification / Alternative check: Assembler manuals and ISA references describe addressing modes in terms of registers, memory, and immediates. Tools like assemblers or linkers are not operands. Why Other Options Are Wrong: Variable, register, and memory location all refer to data sources or sinks for instructions. Common Pitfalls: Confusing compile-time entities (macros, directives) with run-time operands; they influence code generation but are not used by the CPU during execution. Final Answer: Assembler

Question 12

Data transfer methods — which one bypasses the CPU for certain transfers? Choose the technique that moves blocks of data directly between memory and I/O with minimal CPU involvement.

Accepted Answer

Introduction / Context: Modern systems use several strategies to move data between peripherals and memory. Performance and CPU overhead vary significantly among polled I/O, interrupt-driven I/O, and direct memory access (DMA). Selecting the right method is essential for high-throughput or low-latency designs. Given Data / Assumptions: We compare I/O methods: polling, interrupts, and DMA. Goal: identify which method transfers data with minimal CPU intervention during the bulk transfer. Assume a typical DMA controller that arbitrates for the bus. Concept / Approach: With DMA, the CPU sets up the source, destination, and length, then the DMA controller takes over memory bus cycles to move data directly. The CPU is free to execute other tasks until an optional completion interrupt. Polling and interrupts both involve CPU service of each datum or small chunk, increasing overhead. Step-by-Step Solution: Compare methods: polling requires constant CPU checks; interrupts reduce latency but still use CPU for each event.DMA after initialization performs the transfer autonomously.Therefore, DMA is the method that bypasses most CPU activity during the transfer. Verification / Alternative check: Benchmarking shows much higher throughput and lower CPU utilization for DMA-based disk, network, or audio buffers compared to programmed I/O approaches. Why Other Options Are Wrong: Software interrupts and interrupt-driven I/O require CPU service routines; polled I/O uses CPU cycles continuously to check device status. Common Pitfalls: Ignoring bus contention and setup overhead; DMA is best for bulk transfers, not necessarily for single-byte latency-critical events. Final Answer: Direct memory access (DMA)

Question 13

Memory read cycle — what does the CPU fetch? During a general read operation on the system bus, identify what the CPU obtains from the addressed location.

Accepted Answer

Introduction / Context: A CPU interacts with memory through standardized bus cycles. Understanding the semantics of a read cycle clarifies how instructions and data are retrieved, and how the memory system responds to control signals like RD and M/IO on classic buses. Given Data / Assumptions: A read cycle presents an address on the address bus and asserts a read control signal. The memory or I/O device places the contents of that address on the data bus. Instructions are stored as bytes or words in memory; they are fetched as data. Concept / Approach: At the bus level, everything fetched from memory is data. Whether the CPU interprets the fetched bytes as an instruction opcode or as operand data happens after the fetch. Therefore, the fundamental result of a read cycle is that the CPU obtains the data stored at the addressed location. Step-by-Step Solution: CPU outputs address and asserts RD.Memory drives the addressed contents onto the data bus.CPU samples the bus lines and latches the value into internal buffers.Interpretation (instruction vs operand) occurs inside the CPU after the read. Verification / Alternative check: Bus timing diagrams in architecture manuals show that the nature of the content (instruction or data) does not change the electrical read transaction. Why Other Options Are Wrong: “A program instruction” is a subtype of data, but the option “all of the above” incorrectly includes “another address” as a distinct bus-level object; reading an address merely means reading the data that happens to encode an address. Common Pitfalls: Confusing logical meaning with physical bus action. The bus always transports data values; semantics are applied later by the CPU. Final Answer: data itself

Question 14

Pentium hardware width — what is the data bus size? Identify the width of the external data bus used by the classic Intel Pentium (P5-generation).

Accepted Answer

Introduction / Context: The data bus width dictates how many bits can be transferred per bus cycle and strongly influences peak memory bandwidth. The classic Pentium (P5) widened the external data path beyond earlier 80386/80486 designs to improve performance. Given Data / Assumptions: Intel Pentium P5 architecture era. Focus on external data bus width, not internal datapath microarchitecture. Conventional desktop configurations of the time. Concept / Approach: Earlier x86 processors evolved from 16-bit (8086) to 32-bit (80386/80486) internal architectures; however, the external data bus on Pentium was 64 bits wide, enabling double-word fetches per cycle, improving cache line fills and instruction/data bandwidth. Step-by-Step Solution: Recall P5 improvements: superscalar pipeline and wider external data interface.Identify the external data bus width as 64 bits.Select the corresponding option. Verification / Alternative check: Chipset and memory documentation from the era cite 64-bit memory interfaces to the CPU for Pentium systems. Why Other Options Are Wrong: 16-bit and 32-bit reflect older bus widths; 128-bit is typical of later wide interfaces or multi-channel memory systems, not classic P5. Common Pitfalls: Confusing internal register size (32-bit general-purpose registers) with external bus width; they are related but not identical. Final Answer: 64 bits

Question 15

Pentium addressing capability — maximum directly addressable memory space Considering a 32-bit physical address bus, how much memory can a Pentium address?

Accepted Answer

Introduction / Context: The number of address lines determines the maximum directly addressable memory space. For a processor with a 32-bit physical address bus, the theoretical addressable range is a key design constraint for operating systems and hardware designers. Given Data / Assumptions: Pentium-era processors provide 32 physical address lines in mainstream configurations. No paging tricks or segmentation limits are being considered; we refer to raw physical address space. Each unique address selects one byte. Concept / Approach: The physical address space equals 2^(number of address lines). With 32 address lines, that becomes 2^32 byte addresses. Converting 2^32 bytes gives 4,294,967,296 bytes, which equals 4 GB. System implementations may reserve ranges for memory-mapped I/O, but the theoretical maximum remains 4 GB for a 32-bit physical address bus. Step-by-Step Solution: Compute 2^32 = 4,294,967,296.Convert to gigabytes: 4,294,967,296 bytes ≈ 4 GB.Therefore, select 4 GB. Verification / Alternative check: Motherboard documentation from the Pentium era commonly lists 4 GB as the maximum physical address range, with practical limits based on chipset and DIMM support. Why Other Options Are Wrong: 1 MB reflects early 20-bit address spaces (8086 real mode). 1 GB and 2 GB are subsets of the full 4 GB capability. Common Pitfalls: Confusing virtual address space limits with physical addressable memory; operating system choices do not change the bus width capability. Final Answer: 4 GB

Question 16

I/O port behavior — which statement is correct? In programmable I/O systems, what access directions can a port support depending on design and configuration?

Accepted Answer

Introduction / Context: Microcontrollers and peripheral interfaces expose ports that connect the digital world to sensors, actuators, and other chips. The direction of data flow at a port pin depends on the hardware design and configuration registers controlled by software. Given Data / Assumptions: Some ports are input-only (for example, ADC inputs or dedicated status lines). Some ports are output-only (for example, certain driver lines or write-only latches). Many general-purpose I/O ports are configurable as input or output, sometimes per pin. Concept / Approach: Because real systems include all three port types (input-only, output-only, and bidirectional), the most complete answer is that a port can be any of these depending on device and configuration. Configuration registers (for example, DDR/ TRIS/ DIR) often control direction on a per-bit basis in microcontrollers. Step-by-Step Solution: Recognize that direction is a hardware capability configured by software.Identify examples of each type (input-only, output-only, bidirectional).Therefore, choose the inclusive option reflecting all possibilities. Verification / Alternative check: Datasheets for GPIO modules document input, output, and bidirectional settings, including pull-ups, pull-downs, and open-drain or push-pull modes. Why Other Options Are Wrong: Each single-direction option is incomplete; real devices support multiple configurations across different ports or pins. Common Pitfalls: Assuming all ports are symmetrical; some pins have alternate functions or electrical limits that restrict direction or drive strength. Final Answer: all of the above

Question 17

Communication setup terminology — what is the process of jointly establishing communication called? In digital interfaces, identify the term used for the coordinated exchange of control signals to begin data transfer.

Accepted Answer

Introduction / Context: Before data can be exchanged reliably between two digital devices, both sides must agree on readiness and timing. The mechanism by which devices coordinate this readiness is a foundational concept in interface design and bus protocols. Given Data / Assumptions: We consider generic digital links such as CPU to peripheral, or peripheral to peripheral. Control lines like READY, ACK, VALID, or REQUEST are used to coordinate transfer. The question asks for the name of this coordinated process. Concept / Approach: Handshaking is the mutual signaling by which sender and receiver agree when to start, continue, or end a transfer. It can be synchronous (tied to a clock) or asynchronous (event-driven), and may be two-wire (request/acknowledge) or protocol-embedded (for example, in UART start/stop bits). Step-by-Step Solution: Sender asserts a signal indicating data availability or request.Receiver responds with an acknowledge or ready signal.Both sides complete timing constraints and proceed with the transfer.This exchange is called handshaking. Verification / Alternative check: Bus specifications (for example, Centronics, IEEE-488, certain memory bus ready signals) explicitly define handshake sequences to ensure reliable transfer. Why Other Options Are Wrong: DMA is a transfer method; multiplexing shares a medium among signals; bidirectional addressing is not a standard term for link setup. Common Pitfalls: Assuming handshaking requires a separate clock; even asynchronous links use handshake signals to ensure data validity windows. Final Answer: handshaking

Question 18

Interrupt-driven I/O — simultaneous requests In a priority-based interrupt system, if two or more devices assert interrupt requests at exactly the same time, which device will be serviced first?

Accepted Answer

Introduction / Context: Interrupt-driven input/output (I/O) lets peripherals request attention from the processor without constant polling. When several devices assert interrupts at the same instant, the system must decide which one the CPU will service first. Understanding priority resolution is crucial for designing reliable embedded and computer systems. Given Data / Assumptions: Multiple devices can request service concurrently. An interrupt controller or internal CPU logic arbitrates requests. Each interrupt source has an assigned priority level and possibly a vector. Concept / Approach: Most architectures use fixed or programmable priority schemes. A centralized interrupt controller (for example, a PIC) resolves simultaneous requests and forwards only the highest-priority request to the CPU. Lower-priority requests remain pending until the CPU completes the current service routine and re-enables interrupts or performs nested servicing according to policy. Step-by-Step Solution: Define priority: each source has a rank (higher number or lower vector index depending on design).Simultaneous assertion: the controller compares priorities.Result: the highest-priority device wins arbitration and is serviced first.Pending requests: others remain latched and are serviced subsequently when permitted. Verification / Alternative check: Datasheets for programmable interrupt controllers show priority rotation or fixed priority tables; simultaneous requests are deterministically resolved to one highest-priority source, confirming the behavior described. Why Other Options Are Wrong: Closest to CPU / fastest device: physical proximity or intrinsic speed does not determine service order. System crash: robust designs explicitly arbitrate to prevent contention. Lowest vector ignored: vectors map handlers; they are not “ignored” by design. Common Pitfalls: Forgetting that priority can be rotated or dynamically reprogrammed, which still deterministically selects one request first. Final Answer: the device assigned the highest priority is serviced first

Question 19

Historical microprocessors — data bus width of the first commercial CPU Identify the data bus width of the first commercial microprocessor introduced (e.g., Intel 4004).

Accepted Answer

Introduction / Context: The evolution of microprocessors began with very modest word sizes. Knowing the data bus width of the earliest commercial CPU helps place later 8-bit and 16-bit families in historical context and illustrates why early systems focused on simple calculators and control tasks. Given Data / Assumptions: “First microprocessor” refers to the early commercially available CPU-on-a-chip, exemplified by the Intel 4004. Data bus width is the number of bits transferred in parallel for data. Concept / Approach: The Intel 4004 used a 4-bit data path aligned with its original application in desktop calculators, where decimal digits could be conveniently represented as binary-coded decimal (BCD) nibbles. This constrained width simplified the architecture and transistor count of the first-generation microprocessor, paving the way for subsequent 8-bit (8080/8085) and 16-bit (8086) designs. Step-by-Step Solution: Identify the seminal device → Intel 4004 era.Check architecture → 4-bit data path (nibble-oriented).Conclude the answer → 4-bit data bus. Verification / Alternative check: Manufacturer literature and textbooks consistently classify the 4004 as a 4-bit microprocessor, while its successors (e.g., 8008/8080) expanded to 8 bits. Why Other Options Are Wrong: 1-bit/2-bit: too narrow and not representative of the 4004. 8-bit/16-bit: later generations, not the first commercial CPU-on-a-chip. Common Pitfalls: Confusing CPU “word size” with address bus width or instruction length; the earliest device was unequivocally 4-bit in data handling. Final Answer: 4-bit data bus

Question 20

Pentium vs. 8086/8088 — which feature is NOT a Pentium-only enhancement? Choose the option that does not represent a feature added beyond the 8086/8088 era but instead was already present in those earlier processors.

Accepted Answer

Introduction / Context: Comparing the classic 8086/8088 with later Pentium processors highlights how CPU architectures evolved. The Pentium family added performance features such as deeper pipelines, on-chip caches, and superscalar execution. However, some board-level interface traits already existed long before Pentium and therefore are not “enhancements.” Given Data / Assumptions: 8086/8088 external bus used multiplexed lines (AD0–AD15) to carry address and data at different times. Pentium introduced bigger on-chip caches and complex pipelines, and many versions included an on-chip floating-point unit. Concept / Approach: Identify which item in the list was not unique to Pentium as an improvement over 8086/8088. While pipelining and caches were greatly expanded and an internal FPU became standard, the multiplexing of address and data lines was already used by the 8086/8088 to save pins and reduce package size. Thus, that item cannot be a Pentium-era enhancement. Step-by-Step Solution: List Pentium enhancements → larger caches, deeper pipelines, superscalar execution, integrated FPU.Compare with 8086/8088 features → already had AD line multiplexing.Therefore, the non-enhancement is “Data/address line multiplexing.” Verification / Alternative check: 8086 hardware manuals detail ALE-driven demultiplexing of address/data lines. Pentium datasheets emphasize cache and pipeline advances rather than reintroducing multiplexing as a “new” feature. Why Other Options Are Wrong: Pipelined architecture, larger caches, integrated FPU, and superscalar units are hallmark Pentium improvements over early x86. Common Pitfalls: Equating “present in both” with “enhancement”; a feature can persist without being an improvement. Final Answer: Data/address line multiplexing

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