Computer Architecture Basics
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Questions and Answers

What role does instruction alignment play in a superscalar architecture?

  • It ensures instructions retrieve data from memory efficiently.
  • It allows multiple instructions to be fetched simultaneously. (correct)
  • It is critical for preventing memory leaks during instruction execution.
  • It prevents control hazards by avoiding branches.

Which component is essential for handling misaligned instructions in a two-way superscalar processor?

  • Instruction Register
  • Alignment Hardware (correct)
  • Branch Predictor
  • Memory Data Register

In the context of superscalar architectures, what challenge does branch instructions pose?

  • They slow down the data transfer between registers.
  • They increase the time needed for instruction execution.
  • They require more cache memory to store additional data.
  • They introduce control hazards that affect fetch logic. (correct)

What is the main function of the Instruction Fetch (IF) stage in a CPU pipeline?

<p>To retrieve instructions from memory for processing. (B)</p> Signup and view all the answers

Which of the following registers is specifically used for storing the address of the instruction to be fetched next?

<p>Program Counter (A)</p> Signup and view all the answers

Which type of hazard occurs due to dependencies between instructions in a pipeline?

<p>Data Hazards (B)</p> Signup and view all the answers

Which of the following is NOT a type of memory addressing mode?

<p>Floating (B)</p> Signup and view all the answers

What is one key advantage of using pipelining in CPU instruction execution?

<p>It allows multiple instructions to be processed simultaneously. (A)</p> Signup and view all the answers

Which component of the microarchitecture is primarily responsible for executing arithmetic and logic operations?

<p>ALU (D)</p> Signup and view all the answers

What effect does the number of registers have on the efficiency of an Instruction Set Architecture (ISA)?

<p>Limited registers can impede the efficiency of instruction execution. (B)</p> Signup and view all the answers

What is the purpose of microcode in microarchitecture?

<p>To translate complex instructions into simpler micro-operations. (D)</p> Signup and view all the answers

What is the primary function of Instruction Set Architecture (ISA)?

<p>To define the set of instructions a computer can execute (A)</p> Signup and view all the answers

Which of the following is an example of a pipeline stage?

<p>Decode (B)</p> Signup and view all the answers

Which model allows simultaneous access to instructions and data?

<p>Harvard Model (D)</p> Signup and view all the answers

What is a potential consequence of control hazards in a pipeline?

<p>The pipeline may fetch incorrect instructions due to branching. (D)</p> Signup and view all the answers

Which characteristic best describes RISC architecture?

<p>A focus on a small set of efficient operations (D)</p> Signup and view all the answers

What is a key disadvantage of the Von Neumann model?

<p>It is slower due to the single data path for instructions and data (D)</p> Signup and view all the answers

Which of the following describes a primary function of microcode?

<p>To translate complex machine instructions into simpler microinstructions (B)</p> Signup and view all the answers

What differentiates CISC from RISC architectures?

<p>CISC includes a larger set of complex instructions (A)</p> Signup and view all the answers

In the Modified Harvard Model, what feature is prominent?

<p>Combination of separate and shared memory elements (A)</p> Signup and view all the answers

What type of instruction would fall under data movement instructions?

<p>Transferring data between registers (D)</p> Signup and view all the answers

What is a cache hit?

<p>When requested data is found in the cache (D)</p> Signup and view all the answers

Which metric directly affects the performance of a cache?

<p>Block Size (D)</p> Signup and view all the answers

What constitutes a structural hazard in a pipeline?

<p>Multiple instructions requiring the same hardware resources simultaneously. (B)</p> Signup and view all the answers

Which type of data hazard involves an instruction that must wait for a previous instruction's result before proceeding?

<p>Read After Write (RAW) (A)</p> Signup and view all the answers

What is the average memory access time (AMAT) formula?

<p>AMAT = Hit Time + (Miss Rate × Miss Penalty) (C)</p> Signup and view all the answers

What solution involves sending the results of a previous instruction directly to the next instruction without waiting for completion?

<p>Data Forwarding/Bypassing (D)</p> Signup and view all the answers

Which factor generally reduces miss rates in a cache?

<p>Increasing Cache Size (D)</p> Signup and view all the answers

What does superscalar architecture allow in a processor?

<p>Multiple instruction processing per clock cycle (C)</p> Signup and view all the answers

What is a primary purpose of cache memory?

<p>To reduce the average access time to frequently used data. (B)</p> Signup and view all the answers

Which type of cache is located closest to the CPU and is extremely fast but small in size?

<p>L1 Cache (C)</p> Signup and view all the answers

What is a challenge associated with a two-way superscalar architecture?

<p>Frequent pipeline stalls from resource contention (C)</p> Signup and view all the answers

What is a characteristic of a fully associative cache?

<p>Any memory block can be stored in any cache location. (C)</p> Signup and view all the answers

Which of the following describes in-order execution?

<p>Instructions are issued and executed in the order they appear (B)</p> Signup and view all the answers

Which technique involves anticipating what data will be needed soon?

<p>Prefetching (D)</p> Signup and view all the answers

Which cache is designed to store both instructions and data?

<p>Unified Cache (A)</p> Signup and view all the answers

What technique automatically inserts stalls to prevent data hazards?

<p>Pipeline Interlocks (B)</p> Signup and view all the answers

What role does microcode play in a CPU's operation?

<p>It guides CPU components through instruction execution. (B)</p> Signup and view all the answers

What is a significant disadvantage of using microinstructions in CISC architectures?

<p>They can introduce additional latency. (B)</p> Signup and view all the answers

What does pipeline depth refer to in CPU architecture?

<p>The number of stages in the instruction pipeline. (C)</p> Signup and view all the answers

Which of the following best describes a benefit of pipelining in CPU architectures?

<p>Increases instruction throughput over time. (C)</p> Signup and view all the answers

What is a challenge associated with pipelining in CPU design?

<p>It can cause stalls if hazards occur. (B)</p> Signup and view all the answers

Which stage of the pipeline is primarily responsible for retrieving the next instruction?

<p>Instruction Fetch (IF) (A)</p> Signup and view all the answers

How does pipelining contribute to efficient resource usage in CPUs?

<p>By utilizing each pipeline stage simultaneously. (C)</p> Signup and view all the answers

What is one reason why RISC architectures may perform better compared to CISC architectures?

<p>They have fewer layers of execution. (B)</p> Signup and view all the answers

Flashcards

What is Instruction Set Architecture (ISA)?

A set of instructions that a computer can execute. It acts as the interface between the hardware (processor) and software (programs). It defines fundamental aspects like instruction formats, addressing modes, registers, and data types.

What is Microcode?

A lower-level set of instructions used by complex instruction set computing (CISC) CPUs to implement higher-level instructions. It translates complex machine instructions into simpler, sequenced microinstructions. Microcode is stored in special, faster storage within the CPU (like ROM or RAM).

What is the Von Neumann Model?

A traditional architecture where instructions and data share the same memory and data bus. Known for the Von Neumann Bottleneck, as the single data path for instructions and data can cause delays. It is simple and easy to use for general-purpose computing.

What is the Harvard Model?

A design with separate memory and buses for instructions and data. It allows simultaneous access to instructions and data, enhancing performance and reducing potential bottlenecks. Often used in digital signal processing and microcontrollers.

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What is the Modified Harvard Model?

Combines features of both Von Neumann and Harvard models. It allows for transfer between instruction and data memories providing flexibility.

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What is RISC (Reduced Instruction Set Computer)?

It focuses on a minimal set of simple, efficient instructions.

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What is CISC (Complex Instruction Set Computer)?

It uses a larger set of complex instructions, often implemented using microcode for complex tasks.

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What are the different Instruction Types?

They include arithmetic, logical, control, and data movement instructions.

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Instruction Set Architecture (ISA)

The set of instructions understood by a CPU, specifying how operations are performed.

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Registers

Special memory locations within the CPU used to store data and intermediate results during program execution.

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Memory Addressing Modes

Different ways to access data in memory, such as directly, indirectly, or using offsets.

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Pipelining

The method of dividing instruction execution into multiple stages, allowing overlapping and improving performance.

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Fetch

A stage in the pipeline where the instruction is retrieved from memory.

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Decode

A stage in the pipeline where the instruction is translated into control signals.

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Execute

A stage in the pipeline where the instruction is executed.

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Write-back

A stage in the pipeline where the result of the instruction is written back to a register.

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What are Microinstructions?

Microinstructions are small, low-level instructions that control each CPU function in sequence. They allow the CPU to execute complex instructions by breaking them down into simpler steps.

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What is the Microprogram Control Unit?

The Microprogram Control Unit (MCU) is a part of the CPU that stores and manages microinstructions. It uses microcode to guide the execution of instructions by generating signals for various CPU components.

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What is Pipelining?

Pipelining breaks down the CPU's instruction cycle into multiple stages, allowing multiple instructions to be processed simultaneously. It's like a production line for instructions, with each stage responsible for a specific task.

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What are the stages of a pipeline?

The most common pipeline stages include Fetch (IF), Decode (ID), Execute (EX), Memory Access (MEM), and Write-back (WB). Each stage performs a specific task in the instruction cycle.

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What is Pipeline Depth?

Pipeline Depth refers to the number of stages in the pipeline. A deeper pipeline can improve instruction throughput, but can also introduce latency, as instructions can be delayed if there are hazards or waiting for resources.

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What are the benefits of Pipelining?

Pipelining can lead to increased instruction throughput, efficient use of CPU resources, and reduced latency per instruction. It allows the CPU to process multiple instructions concurrently.

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What are the challenges of Pipelining?

Pipelining can be complex to manage and is susceptible to hazards, which can cause the pipeline to stall and reduce efficiency. Hazards occur when instructions depend on each other and cannot be processed in the expected order.

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Instruction Alignment

A technique in superscalar architectures that places instructions in the correct memory locations for efficient retrieval. It involves aligning instructions to the correct execution units, ensuring the processor can fetch and execute them simultaneously.

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RISC (Reduced Instruction Set Computer)

A CPU design that prioritizes a minimal set of simple, efficient instructions.

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Instruction Fetching

The process of retrieving instructions from memory and preparing them for execution.

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CISC (Complex Instruction Set Computer)

A type of computer design that uses a larger set of complex instructions, often implemented using microcode.

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Branch Prediction

A method that predicts the outcome of branch instructions, allowing the CPU to fetch instructions ahead of time and maintain pipeline efficiency.

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Data Hazard

A type of pipeline hazard that occurs when an instruction needs the result of a previous instruction that has not yet completed. This creates a dependency between instructions.

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Data Forwarding

A technique used for handling data hazards where the result of an instruction is forwarded directly to the next instruction without waiting for it to complete execution.

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Stalling

An approach to managing data hazards where the execution pipeline is paused until the required data becomes available. This prevents incorrect results by waiting for necessary information.

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What is a cache?

A type of memory designed to store frequently used data and instructions close to the CPU, reducing the time spent accessing main memory.

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What is an Instruction Cache (I-Cache)?

A cache specifically designed to store instructions that are frequently used by the processor. It speeds up the instruction fetch process.

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What is a Data Cache (D-Cache)?

A cache dedicated to storing data that the CPU frequently needs to access. It accelerates data retrieval.

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Direct-Mapped Cache

A caching technique where each memory block can only be stored in one specific location within the cache. This makes it simple but can lead to collisions.

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Fully Associative Cache

A caching technique where any memory block can be stored in any available location within the cache. This provides flexibility but requires more complex management.

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Set-Associative Cache

A type of cache that divides memory blocks into sets, allowing data to be placed in any location within its designated set. This helps reduce conflict misses compared to direct-mapped caches.

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Superscalar Architecture

A processor design that can execute multiple instructions simultaneously during each clock cycle.

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Cache Hit Rate

The percentage of memory requests that are successfully found in the cache.

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Cache Miss Rate

The percentage of memory requests that are not found in the cache, requiring data retrieval from main memory.

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Miss Penalty

The additional time needed to fetch data from main memory when a cache miss occurs.

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In-Order Execution

Instructions are processed in the exact order they appear in the program.

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Two-Way Superscalar

A type of superscalar architecture that can execute two instructions simultaneously per clock cycle.

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Fetch Logic

The component responsible for retrieving instructions from memory and delivering them to the processor's pipeline.

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Study Notes

Instruction Set Architecture (ISA)

  • Defines the set of instructions a computer can execute.
  • Acts as an interface between hardware and software.
  • Determines instruction formats, addressing modes, registers, and data types.

Microcode

  • A lower-level set of instructions used by complex CPUs to implement higher-level instructions.
  • Translates complex machine instructions into simpler, sequenced microinstructions.
  • Stored in special, faster storage within the CPU (e.g., ROM or RAM).

Machine Models

  • Von Neumann Model
    • Instructions and data share the same memory and data bus.
    • Known for the Von Neumann Bottleneck (delays).
    • Simple and easy for general purpose computing.
  • Harvard Model
    • Separate memory and buses for instructions and data.
    • Allows simultaneous access, increasing performance and reducing bottlenecks.
    • Often used in digital signal processing and microcontrollers.
  • Modified Harvard Model
    • Combines features of Von Neumann and Harvard.
    • Allows transfer between instruction and data memories.
    • Adds flexibility and is common in modern CPUs.

ISA Characteristics

  • Complexity:

    • RISC (Reduced Instruction Set Computer): Simple and minimal instructions.
    • CISC (Complex Instruction Set Computer): Larger set of complex instructions.

  • Instruction Types and Formats:

    • Include arithmetic, logical, control, and data movement instructions.
    • Varying sizes and formats based on operation types.

  • Registers:

    • Defines types and numbers of registers (general-purpose, floating-point).
    • Limited numbers, affecting ISA efficiency.

  • Memory Addressing Modes:

    • Various methods, including immediate, direct, indirect, indexed, and base-plus-offset.
    • Affects program's ability to access data.

  • Data Types: Defines supported data types (integers, floating-point, characters, etc.).

Pipeline

  • Basic Concept:

    • Divides instruction execution into stages (fetch, decode, execute, memory access, write-back).
    • Allows simultaneous processing, improving throughput.

  • Pipeline Stages:

    • Fetch: Retrieves the instruction.
    • Decode: Decodes the instruction.
    • Execute: Performs the operation.
    • Memory Access: Accesses memory.
    • Write-back: Stores the result.

  • Pipeline Hazards:

    • Data Hazards: Instructions depend on previous results.
    • Control Hazards: Pipeline encounters branch instructions.
    • Structural Hazards: Insufficient resources for parallel execution.

  • Advantages of Pipelining:

    • Higher throughput (more instructions in shorter time)
    • Efficient CPU resource utilization (reduces idle time)
    • Improved performance (Higher IPC)

Microcoded Microarchitecture

  • Refers to the internal CPU architecture implementing ISA instructions.

  • Consists of functional blocks like ALU, control unit, registers, and cache.

  • Microcode translates complex instructions into simpler micro-operations.

    • Controls each CPU function in sequence.
    • Enables complex instruction execution, especially in CISC architectures.

  • Microprogram Control Unit: Stores and manages microinstructions in high-speed memory.

Cache

  • Purpose: Small, high-speed memory near the CPU, storing frequently accessed data and instructions.

  • Reduces average access time from main memory.

  • Types:

    • Instruction Cache (I-Cache): Stores instructions.
    • Data Cache (D-Cache): Stores data.
    • Unified Cache: Stores both.

  • Levels:

    • L1 Cache: Closest to CPU, fast but small.
    • L2 Cache: Larger, slightly slower.
    • L3 Cache: Larger, shared among cores, slower.

  • Mapping Techniques:

    • Direct-Mapped: Each memory block maps to exactly one cache location.
    • Fully Associative: Any memory block can be stored in any cache location.
    • Set-Associative: Compromise between the two.

  • Performance Metrics:

    • Hit Rate: Percentage of accesses where data is in the cache.
    • Miss Rate: Percentage of accesses where data is not in the cache.
    • Miss Penalty: Extra time to retrieve data from main memory.
    • AMAT (Average Memory Access Time): Hit Time + (Miss Rate x Miss Penalty).

Control Hazards

  • Occur when pipeline encounters instructions altering program counter (PC) like jumps/branches.

  • Can cause pipeline stalls, reducing efficiency.

  • Types of Control Hazards:

    • Jump Instructions (unconditional, PC set to a new address).
    • Branch Instructions (conditional, altering PC based on conditions)
    • Potential Pipeline Impacts: If branch is taken, instructions after branch must be discarded.

  • Solutions:

    • Branch Prediction for quicker branch decisions (static/dynamic).

Superscalar Architecture

  • A processor design that issues and executes multiple instructions per clock cycle.

  • Increase instruction-level parallelism.

  • Requires multiple execution units for simultaneous instruction processing.

  • In-Order Execution: Issues and executes instructions in program order, can have pipeline stalls if dependent instructions need same resources.

  • Challenges : Requires careful handling of instruction dependencies , can cause pipelines stalls.

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Unit IV: Instruction Set Architecture PDF

Description

This quiz covers fundamental concepts of computer architecture, including Instruction Set Architecture (ISA), microcode, and different machine models such as Von Neumann and Harvard. Test your understanding of these key principles that bridge hardware and software in computing systems.

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