Modern Computer Architecture: How GPUs and LLMs are Reshaping the Field

Jim Ledin, with over 30 years of experience in embedded systems, has consistently focused on the intersection of hardware and software. His expertise also extends to penetration testing and cybersecurity, underscoring his comprehensive understanding of system vulnerabilities and robust design. His career has been dedicated to real-time and embedded systems, where the interplay between physical components and code is critical for functionality and performance.

Ledin's fascination with computer architecture began in the 1980s with a Commodore 64. He initially learned BASIC but quickly encountered performance limitations when trying to draw on the screen using a joystick. This led him to explore 6502 assembly language. He meticulously assembled code manually on paper to optimize these slow graphical operations, an experience that instilled a deep appreciation for low-level programming efficiency. He said, "I had a Commodore 64 and I learned a little basic and wrote a program to do some screen drawing using the joystick and it was extremely painfully slow. So, I took an interest in the assembly code."

While direct use of assembly language is rare in contemporary application development, understanding low-level architecture remains crucial for engineers. Knowledge of various processor architectures, such as ARM, Intel, or RISC-V, and their assembly-level optimizations, provides valuable insight. This understanding can significantly enhance an engineer's ability to efficiently solve high-level problems on these systems. As Jim Ledin noted, "understanding what's there, um what particular different types of processors, whether it's ARM or Intel or RISC-V is sort of optimized to do at the assembly language level can inform how you go about solving high-level problems on those systems most efficiently."

The third edition of Ledin's book, "Modern Computer Architecture and Organization," introduces new chapters dedicated to Graphics Processing Units (GPUs) and Large Language Models (LLMs). This expansion acknowledges the rapid evolution of these technologies, which contrasts sharply with the stable nature of architectures like x86 or digital logic that have remained consistent for years. MJ highlighted the challenge of writing content that risks quickly becoming outdated due to the dynamic pace of innovation in AI hardware. He stated, "most of this book covers architecture that's been stable for years. Things like x86 or digital logic, which don't really shift month to month. But when we talk about GPUs and LLM architecture, they do."

A fundamental engineering challenge in modern computer architecture revolves around how hardware components are interconnected. The effectiveness of these connections in providing the necessary communication bandwidth is crucial for achieving expected performance levels. The discussion specifically explores architectural bottlenecks that can impede system performance. Jim Ledin underscored this point, asking, "are they connected to each other to provide the communication bandwidth that's required to get the level of performance that we all expect?"

GPU hardware evolution tends to be iterative rather than revolutionary, with annual updates primarily focusing on increasing capacity and improving memory access speeds. Jim Ledin explained that new GPU generations are not radical departures from previous ones; instead, they integrate more of the same capabilities into the chip. The core functionalities and architectural principles of GPUs have remained largely consistent over time, with advancements centered on refining existing components to handle larger workloads and faster data retrieval. He noted, "they're not radical departures from previous generations. A lot of it is just putting more of the same kinds of capability into the chip, and improving things like the memory access speed."

GPUs, originally designed for rendering video frames in 3D gaming, have proven to be accidentally well-suited for artificial intelligence tasks, particularly Large Language Models (LLMs). This suitability stems from a significant mathematical similarity between the calculations required for generating video images and those involved in language model processing. Neural network processing, which is at the heart of LLMs, relies heavily on massive matrix multiplications, a task GPUs excel at due to their parallel processing capabilities. Jim Ledin emphasized this, stating, "there is a great deal of similarity between the calculations that go on to generate video images and the processing in a language model."

A significant portion of Large Language Model (LLM) processing, specifically 80% to 90%, is dominated by matrix multiplications. These operations, often involving tensors treated as multi-dimensional arrays, are the fundamental building blocks of neural networks. Modern AI hardware is specifically optimized to perform these calculations efficiently. The process can be broken down into a series of smaller matrix multiplications, with the results then accumulated to form the final output. Hardware is designed to handle these computations by processing small blocks, such as 16x16 matrices, in parallel to achieve the high performance required for complex AI tasks. As Jim Ledin explained, "80 to 90% of the processing comes down to matrix multiplications. ... In fact, that can be broken down into a series of matrix multiplications and then accumulating the results of those."