Technology Sharing

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Table of Contents

1. Computer Architecture

2. Harvard Architecture

3. Improved Harvard Architecture

4. Von Neumann Architecture

5. Structural comparison

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1. Computer Architecture

Computer architecture refers to the way a computer system is organized and implemented, including its hardware components and the relationships between them. The design of the architecture directly affects the performance, efficiency, and flexibility of the computer.

Computer architecture covers multiple levels, from the lowest-level hardware implementation (such as processor, memory, input and output devices, etc.) to the upper-level system software (such as operating system, compiler, etc.). Each level needs to be carefully designed to meet specific performance and functional requirements.

In computer architecture, there are two main models: Von Neumann Architecture and Harvard Architecture. Von Neumann Architecture is a traditional computer design model that uses a unified memory space to store program instructions and data. Harvard Architecture uses separate memory spaces to store program instructions and data separately to improve system performance. Both architectures have their own advantages and disadvantages and are widely used in different application scenarios.

2. Harvard Architecture

Harvard architecture refers to the storage of instructions and data in different memories, and the CPU accesses instructions and data separately through independent buses. This architecture was first used in Harvard University's Mark I computer, hence the name.

Features：

• Separate storage: The instruction memory and data memory are separate.
• Independent bus: The CPU accesses the instruction memory and data memory separately through independent buses, which means that the CPU can read instructions and data at the same time.
• Parallel Processing: Due to the independent access of instructions and data, the CPU can process instruction fetch and data operations in parallel, improving processing efficiency.

advantage：

• high performance: Ability to access instructions and data simultaneously, reducing waiting time and increasing execution speed.
• Reduce Conflict：The separate storage of instructions and data avoids bus conflicts and improves system throughput.

shortcoming：

• Complex design: Two independent memories and bus systems are required, which increases the complexity of design and implementation.
• Less flexibility：The program and data storage space is fixed and not as flexible as the von Neumann architecture.

application： The Harvard architecture is widely used in digital signal processors (DSPs), microcontrollers and some embedded systems, such as the ARM Cortex-M series chips.

3. Improved Harvard Architecture

• ARM7 and earlier chips: Adopts von Neumann architecture, with instructions and data sharing memory and bus, suitable for early simple computing and control tasks.
• Chips after ARM7: It adopts an improved Harvard architecture and provides higher processing efficiency and performance by separating instruction and data memory. It is widely used in modern embedded systems and microcontrollers.

In the improved Harvard architecture, the system combines the advantages of the Harvard architecture and the von Neumann architecture and adopts a hybrid storage method. This architecture introduces instruction cache and data cache in the design, thereby improving the performance and efficiency of the processor.

• CPUConnected via separate busInstruction CacheandData Cache。
• External Memory：Instructions and data are mixed and stored in the external memory and loaded into the internal cache through the cache mechanism.
• Parallel access: The CPU can read instructions from the instruction cache and read and write data from the data cache at the same time, improving execution efficiency.

Features

1. Instruction Cache and Data Cache：

   • Independent Cache: Instructions and data are stored in separate caches. When the CPU executes instructions, it fetches instructions from the instruction cache and reads and writes data from the data cache.
   • Parallel access: Because the instruction and data caches are independent, the CPU can access instructions and data in parallel, thereby improving execution efficiency.

2. Hybrid storage of external memory：

   • Unified Memory: In the external memory, instructions and data are stored mixedly, similar to the von Neumann architecture.
   • Cache mechanism: The cache mechanism allows the CPU to load instructions and data from a unified external memory into independent instruction cache and data cache.

advantage

1. high performance：

   • Reduce waiting time: Through independent instruction cache and data cache, the CPU can obtain instructions and data at the same time, reducing waiting time and improving instruction execution speed.
   • High cache hit rate: Due to the introduction of cache, frequently accessed data and instructions can be quickly read in the cache, improving the system's response speed.

2. Flexibility and efficiency：

   • Unified storage flexibility: The hybrid storage method of external memory maintains the flexibility of the von Neumann architecture, allowing programs and data to dynamically allocate storage space.
   • Cache Management: Through cache management, the system can effectively utilize memory bandwidth, reduce bus conflicts, and improve overall system efficiency.

3. Simplified design：

   • Unified Memory Interface: Although independent instruction and data caches are used internally, access to external memory is still through a unified interface, simplifying memory management.

shortcoming

1. Design Complexity：

   • Cache Coherence: It is necessary to ensure the consistency of instruction cache and data cache, which increases the complexity of design and implementation.
   • Cache Management: The introduction of cache requires complex cache management mechanisms, such as cache replacement strategies, cache consistency protocols, etc.

2. Increased power consumption：

   • Additional Hardware: The added cache hardware and management logic may result in increased system power consumption, which requires special consideration in power-sensitive applications.

Application Areas

The improved Harvard architecture is widely used in high-performance processors and embedded systems, especially those application scenarios that require efficient processing of instructions and data at the same time. Typical applications include:

• Smartphones and tablets: Need to efficiently handle multi-tasking and complex multimedia applications.
• Embedded control system：Scenarios that require high real-time performance and high reliability, such as industrial control, robotics, and automotive electronics.
• High Performance Computing：Such as servers and data centers, computing tasks that require high throughput and high efficiency.

4. Von Neumann Architecture

The von Neumann architecture is a computer design model proposed by John von Neumann. It uses a unified memory space to store program instructions and data, and the CPU accesses instructions and data sequentially through the same bus.

Features：

• Unified Storage: Instructions and data are stored in the same memory.
• Single bus: The CPU accesses instructions and data in the memory sequentially through a single bus.
• Sequential execution：The CPU reads instructions and data from the memory in sequence and executes them one by one.

advantage：

• Simple design: Unified memory and single bus system, which is relatively simple to design and implement.
• High flexibility：Programs and data share the same storage space, and storage requirements can be adjusted dynamically.

shortcoming：

• Performance bottleneck: Since instructions and data are transmitted through the same bus, the CPU cannot read instructions and data at the same time, which may lead to the "von Neumann bottleneck" and limit performance.
• Bus Conflict：Instructions and data share the bus, which may cause bus conflicts and affect system efficiency.

application： The von Neumann architecture is widely used in general-purpose computing devices such as personal computers, servers, and embedded systems, such as ARM's early ARM7 chip.

5. Structural comparison

Memory structure

• Von Neumann Architecture：

  • Unified Memory: Program instructions and data are stored in the same memory and accessed using a single memory bus.
  • Single data path: Since instructions and data share the same bus, the CPU can only perform one memory access (either fetching instructions or reading/writing data) per clock cycle.

• Harvard Architecture：

  • Separate storage: Program instructions and data are stored in different memories, and independent memory buses are used to access instructions and data respectively.
  • Independent data paths: The CPU can fetch instructions from the instruction memory and read/write data from the data memory at the same time, achieving parallel access.

Performance and efficiency

• Von Neumann Architecture：

  • Performance bottleneck: Since instructions and data share the same memory bus, the "von Neumann bottleneck" is prone to occur, limiting the system's parallel processing capabilities and overall performance.
  • Simple and flexible：It is relatively simple to design and implement, suitable for a variety of general computing tasks, and has high flexibility.

• Harvard Architecture：

  • high performance: Since instructions and data are stored in different memories, the CPU can obtain instructions and data in parallel, greatly improving processing efficiency.
  • Reduce Conflict：Independent instruction and data buses reduce bus conflicts and improve system throughput and execution efficiency.

Design complexity

• Von Neumann Architecture：

  • Simple design: A single memory and bus system, which is relatively simple to design and implement.
  • Easy maintenance: Due to its simple structure, the maintenance and debugging of the system is relatively easy.

• Harvard Architecture：

  • Complex design: Two independent memories and bus systems are required, which increases the complexity of design and implementation.
  • Complex maintenance: Due to the independent memory system, the maintenance and debugging of the system are relatively complicated.

Application Areas

• Von Neumann Architecture：

  • General computing devices: Widely used in personal computers, servers and embedded systems, such as x86 architecture processors.
  • Early microcontrollers: Such as some microcontrollers based on 8051 architecture, used for simple control tasks.

• Harvard Architecture：

  • Embedded Systems and Microcontrollers: Such as ARM Cortex-M series microcontrollers, used for real-time control and efficient data processing.
  • Digital Signal Processor (DSP): Such as TI's C6000 series, used for audio processing, communication systems and image processing.

Summarize