Classifications of Computer Architecture

Summary

This lecture delves into the classifications of computer architecture, focusing on two main models: Von Neumann and Harvard. Von Neumann architecture, also known as Princeton architecture, features a single path between the CPU and memory, leading to the Von Neumann bottleneck. In contrast, Harvard architecture separates instruction and data memory to overcome this limitation. The session also covers Flynn's taxonomy, categorizing architectures based on instruction and data streams, with SISD, SIMD, MISD, and MIMD types, providing a foundational understanding for modern processor design.

Takeaways

• 🏛️ Computer architecture is classified into two main categories: Von Neumann architecture and non-Von Neumann architecture.
• 🔍 Von Neumann machines have three basic hardware subsystems: CPU, main memory, and I/O system, and they operate as stored program computers with sequential instruction execution.
• 🔄 The Von Neumann bottleneck occurs when data and instructions share a single memory pathway, limiting simultaneous instruction and data processing.
• 🏫 The Harvard architecture, proposed by Harvard University, overcomes the Von Neumann bottleneck by using separate memory units for instructions and data, allowing parallel processing.
• 🛠️ Modified Harvard architecture combines elements of both Harvard and Von Neumann architectures, with a small, fast cache memory that can act as either depending on the access mode.
• 🤖 Flynn's taxonomy classifies computer architectures based on the number of instruction streams and data streams, such as SISD, SIMD, MISD, and MIMD.
• 🔢 SISD (Single Instruction Stream, Single Data Stream) is the category where Von Neumann architecture falls, with one CPU executing one instruction at a time.
• 🌟 SIMD (Single Instruction Stream, Multiple Data Stream) machines have multiple ALUs executing the same operation on different data sets in parallel, controlled by a single control unit.
• 🛑 MISD (Multiple Instruction Streams, Single Data Stream) is a theoretical category with no practical implementation, where different instructions operate on the same data item.
• 🔄 MIMD (Multiple Instruction Streams, Multiple Data Streams) refers to multiprocessors with independent processors, each executing different instructions on different data sets.
• 📚 Michael J. Flynn's classification system has been instrumental in the design and functionality of modern processors since its introduction in 1966.

Q & A

What are the two broad classifications of computer architecture discussed in the script?

The two broad classifications of computer architecture discussed are Von Neumann architecture and non-Von Neumann architecture.

What are the three basic hardware subsystems of a Von Neumann machine?

The three basic hardware subsystems of a Von Neumann machine are the CPU, the main memory, and the I/O system.

What is the main characteristic that defines a stored program computer?

A stored program computer is defined by its ability to hold the program controlling the computer operation in the main memory, allowing the computer to manipulate its own program as well as any other data stored inside the memory.

What is the 'Von Neumann bottleneck' and why does it occur?

The 'Von Neumann bottleneck' refers to the limitation where a processor cannot simultaneously read an instruction and operate on data because both instructions and data are fetched over the same path. This occurs in systems with pure Von Neumann architecture where instructions and data are stored in the same memory unit.

What is the Harvard architecture and how does it differ from the Von Neumann architecture?

The Harvard architecture is a model that uses separate memory units for storing instructions and data items. This allows the processor to read an instruction and perform data memory access simultaneously, unlike the Von Neumann architecture where both operations share a single memory pathway.

What is the Modified Harvard architecture and how does it combine features of both Harvard and Von Neumann architectures?

The Modified Harvard architecture is similar to the Harvard architecture but it relaxes the strict division of instruction memory and data memory. It includes a small, fast memory storage called caching. When the processor executes from the cache, it acts like a pure Harvard architecture, and when accessing from the backing memory, it acts like a pure Von Neumann machine.

What does SISD stand for in computer architecture and what are its characteristics?

SISD stands for Single Instruction Stream, Single Data Stream. Computers in this category have one CPU that executes one instruction at a time and fetches and stores one item of data at a time.

What is SIMD and how does it differ from SISD?

SIMD stands for Single Instruction Stream, Multiple Data Stream. Unlike SISD, SIMD machines have a control unit that operates like a Von Neumann machine executing a single instruction stream, but they have more than one ALU, allowing the execution of the same operation on different sets of data items in lock steps.

What is the difference between MISD and MIMD in Flynn's taxonomy?

MISD stands for Multiple Instruction Streams, Single Data Stream, where theoretically different programs would execute on the same data items. MIMD stands for Multiple Instruction Streams, Multiple Data Streams, where each processor can execute a different set of instructions on its own set of data, making it suitable for parallel processing.

Who proposed the classification model used to categorize computer architectures by the number of processors, programs, and memory structures?

The classification model was proposed by Michael J. Flynn in 1966, and it is commonly known as Flynn's taxonomy.

What is the significance of Flynn's taxonomy in the design of modern processors?

Flynn's taxonomy is significant as it has been used as a tool in the design of modern processors and their functionalities, helping to understand and categorize different types of computer architectures based on their instruction and data handling capabilities.