Understanding Multi-CPU Systems: Can a Computer Function with Just One CPU and Multiple Cores?

In the realm of computer architecture, the choice of a single processor or multiple CPUs is often driven by the specific requirements of the system. Whether a high-end PC or a small device like an Airpod, these differing needs necessitate a variety of CPUs tailored to their respective functions. This article explores the concept of multi-CPU systems, the role of CPUs with multiple cores, and the evolution of instruction set architectures, highlighting the significance of RISC-V in this landscape.

The Role of Multiple CPUs in Computing

Modern computing tasks often have distinct demands in terms of processor speed and electrical power availability. For instance, a high-end PC or server might require a CPU with a significantly larger die size, such as 250 mm2, and a high power consumption of 400W. Conversely, devices like Airpods feature CPUs that are much smaller in size, typically a fraction of a mm2, and must operate efficiently with limited power resources from a tiny battery.

Despite such differences, it is entirely feasible to use the same instruction set in both scenarios, albeit with vastly different performance outcomes. This adaptability is due to the concept of Instruction Set Architecture (ISA), which allows for a wide range of CPU implementations at various price points and performance levels.

The Historical Evolution of Instruction Set Architectures (ISAs)

The idea of an ISA with diverse implementations can be traced back to IBM’s System/360 range in 1964. IBM pioneered this approach to cater to a broad spectrum of computing needs. Historically, however, ISAs have been proprietary, with ownership and legal restrictions preventing other companies from building compatible systems. As a result, numerous companies had to create their own unique ISAs, leading to a diverse and incompatibility-ridden ecosystem.

Starting around the year 2000, the landscape shifted towards a dominant few ISAs. The x86 architecture, owned by Intel, became the standard. AMD had a permanent license, and Arm Holdings PLC acquired the Arm architecture. These ISAs became ubiquitous, while others, such as Intel's 64-bit ISA, became obsolete.

Despite this concentration, there are still some notable exceptions. IBM’s zSystem, derived from S/360 and POWER, as well as MIPS and a few microcontroller ISAs, continue to thrive in niche markets.

The Rise of RISC-V: An Open Standard ISA

One significant development in the field of ISAs is the rise of RISC-V, an open specification ISA that is becoming increasingly popular. RISC-V is freely available for anyone to build compatible CPUs, making it a promising alternative to proprietary ISAs. This open-source architecture is gaining traction due to its flexibility and adaptability, supporting both 32-bit and 64-bit versions with a consistent instruction set.

Academics at Berkeley University initiated the development of RISC-V in 2010. By 2015, they released a stable draft of the main user mode instructions and established a non-profit foundation to manage the specification. The final frozen specification of RISC-V will only be updated as needed, ensuring stability and backward compatibility.

RISC-V’s popularity is growing, indicating a potential shift towards more open and collaborative standards in the future. This could lead to more uniformity in hardware design, easier integration, and greater innovation in the computing industry.

Conclusion: Can a Computer Function with Just One CPU and Multiple Cores?

The choice between a single CPU with multiple cores or multiple CPUs depends on the specific requirements of the system. A computer can indeed function with just one CPU and multiple cores, as evidenced by the successful implementation in modern devices. However, the advent of multi-CPU systems and the growing adoption of RISC-V suggest a future where hardware flexibility and compatibility play increasingly important roles.

As technology continues to advance, the landscape of ISAs will likely evolve further, driven by a balance between proprietary control and open standards. RISC-V, in particular, represents a significant step forward in this direction, offering a flexible and open alternative to the dominant proprietary ISAs.