Von Neumann Architecture Fundamentals
📌 Modern computers primarily use the von Neumann model, developed in 1945, which features three main components: the CPU, read/write main memory, and Input/Output (I/O) devices.
💾 Main memory (often holding a billion words or more, with widths $\geq 32$ bits) stores both the instructions for the CPU and the data.
🔗 Instructions are binary values interpreted by the control logic, containing fields like the opcode specifying the operation (e.g., ADD, XOR) and fields defining source/destination registers.

CPU Components and Operation
🧠 The system design comprises the datapath (performing storage and manipulation via registers and the ALU) and the control unit (the "brain" interpreting instructions).
🔢 The control unit includes a program counter tracking the next instruction address and logic to translate instruction fields into control signals (e.g., ASEL, BSEL, DEST, FN function code for the ALU).
🔄 Instruction execution follows a cycle: fetch instruction via the program counter, convert fields to control signals, execute operation in the ALU, store the result, and update the program counter for the next instruction, with modern machines executing billions of instructions per second.

Instruction Set Architecture (ISA) and Design Trade-offs
📜 The Instruction Set Architecture (ISA) is the functional specification defining operations and storage mechanisms, acting as a contract between hardware designers and programmers.
⏳ Successful ISAs can last for decades across many technology generations (e.g., Intel x86 performance increased from $300,000$ to $5$ billion instructions per second over fifteen years for the same ISA).
📊 Designing an ISA requires a quantitative approach using benchmark programs to evaluate performance metrics like execution speed or energy consumption based on the intended application (e.g., smartwatch vs. server).

Key Points & Insights
➡️ The distinction between instruction and data in main memory is determined solely by how the CPU uses the value (loaded by control logic vs. loaded into the datapath).
➡️ A core design principle is to identify common operations (like simple arithmetic and memory access) and optimize them for speed and energy efficiency.
➡️ The ISA acts as an essential layer of abstraction, allowing hardware improvements without immediately requiring software changes, provided old software compatibility is maintained.

📸 Video summarized with SummaryTube.com on Nov 16, 2025, 12:41 UTC