Here, we examine the advantages and disadvantages of using RISC-V, MIPS, CAIRO, and custom ISAs for zkVMs. Each architecture presents distinct benefits in areas like scalability, maturity, and suitability for ZK applications. By analyzing these architectures, we aim to clarify which environments and use cases are best suited for each approach, particularly in the context of zkVM development.
zkVM’s are becoming increasingly important for blockchain scalability, connectivity, privacy-preserving computations, and general-purpose cryptographic use cases. The underlying architecture of these zkVMs can significantly influence their performance, efficiency, scalability, and adoption. We focus on examining four contenders in this field: RISC-V, MIPS, CAIRO, and custom ISAs such as @0xLita's Valida. We have strived to objectively explore each of these architectures in depth, presenting a comparative analysis that takes into account factors such as openness, scalability, community support, hardware availability, and specific ZK optimizations.
RISC-V is an open-source, royalty-free architecture that has rapidly gained popularity due to its flexibility and extensibility. This open standard encourages wide-scale adoption and community-driven enhancements, which can be particularly advantageous in the zkVM ecosystem. The architecture's modular design supports scalability, enabling developers to implement custom extensions tailored for zkVM-specific requirements without incurring licensing costs. The freedom to adapt and extend RISC-V is potentially an asset for ZK applications, which frequently evolves with new cryptographic methods.
RISC-V's scalability stems from its modular ISA, which allows it to be used in diverse applications, from microcontrollers to full-fledged processors for zkVMs. This adaptability makes it a versatile choice for ZK applications, which can vary widely in computational complexity and resource requirements. Furthermore, RISC-V's community support has led to the development of a broad ecosystem of tools and libraries, facilitating innovation in zkVM implementations.
RISC-V zkVMs, such as those developed by @SuccinctLabs and @RiscZero, benefit from compatibility with high-level programming languages like Rust, which streamlines the development process by offering a rich set of libraries and strong community support. RISC-V is supported by major compiler frameworks, including the GNU Compiler Collection (GCC) and LLVM, enabling compilation from high-level languages such as C, C++, and Rust into RISC-V machine code, which facilitates software development.
In real-world implementations, RISC-V CPUs often incorporate multiple extensions beyond the base ISA, leading to increased complexity. A realistic ISA count for practical RISC-V implementations is around 100 instructions, which can affect the efficiency of proof generation due to the larger instruction set. While the modularity of RISC-V allows for tailored customization, it also leads to market fragmentation, particularly in applications like IoT where consistency is crucial. This fragmentation can limit the effectiveness of RISC-V zkVMs in covering non-blockchain use cases effectively.
Specialized ISAs, such as those developed by Lita, focus directly on zkVM performance by minimizing instruction set complexity and enhancing zk-specific operations. Such targeted approaches can potentially outperform general-purpose RISC-V zkVMs, particularly in environments demanding high efficiency and streamlined proof generation.
MIPS has a long history of use in embedded systems, networking, and consumer electronics, with decades of stability and optimizations that provide a mature platform for zkVMs, such as @ProjectZKM’s zkMIPS. This legacy architecture comes with an extensive range of hardware support and established industry standards. The inherent stability of MIPS, coupled with its well-developed DSP and SIMD extensions, makes it well-suited for specific proof workloads that require optimized processing capabilities.
MIPS’ established hardware ecosystem is a significant advantage in practical deployment scenarios. The existence of commercial, off-the-shelf hardware designed for MIPS can enable faster deployment for zkVM projects compared to RISC-V, which still has comparatively fewer hardware options available. Additionally, MIPS' long history has created a highly mature software stack that can be adapted for zkVM use cases with minimal friction.
MIPS has long-standing support in compiler toolchains like GCC and LLVM, allowing developers to compile high-level languages into MIPS machine code. This support extends to languages such as C and C++, leveraging the architecture's features for diverse applications. This compatibility is comparable to that of RISC-V, ensuring that MIPS remains a viable option for software development within zkVM environments.
CAIRO is an architecture developed by @StarkWareLtd specifically for ZK applications, aiming to reduce overhead and maximize the efficiency of proof generation. Its instruction set and execution model are tailored to suit the requirements of zkVMs, making it a highly specialized solution in the ZK space. The CAIRO architecture integrates closely with blockchain environments like @Starknet, which leverage its ZK capabilities for enhanced scalability.
By focusing solely on zero-knowledge applications, CAIRO minimizes the general-purpose computational burden and improves proving efficiency compared to general ISAs like RISC-V or MIPS.
While CAIRO's specialization in ZK provides significant advantages in specific blockchain environments, it lacks the versatility of RISC-V and MIPS for broader applications. Developers may find CAIRO less flexible, as it does not support the same level of general-purpose computing. Furthermore, CAIRO's hardware support is currently more limited, relying on specialized implementations rather than a widely available commercial ecosystem.
Custom ISAs, such as Lita's Valida, are designed specifically to optimize zkVM performance by focusing on proof generation. These ISAs reduce computational overhead by eliminating unnecessary instructions and enhancing zk-specific operations, which can lead to more efficient execution and faster proof times. By targeting zk-specific needs, custom ISAs provide an edge in performance that general-purpose ISAs may not achieve.
Custom ISAs aim to streamline zkVM operations by simplifying the instruction set to include only zk-relevant operations. This reduced complexity can significantly enhance proof generation efficiency, making custom ISAs an attractive option for zkVM implementations that demand high performance and minimal latency. Lita's Valida zkVM, for instance, is tailored to achieve high zk-proving efficiency, providing a direct performance advantage over more generalized ISAs.
Despite their performance benefits, custom ISAs come with notable challenges. Developing a custom ISA requires significant resources to build a new compiler toolchain and high-level language support, which can be resource-intensive. The lack of mature development tools, libraries, and hardware support also limits the adoption of custom ISAs compared to established ISAs like RISC-V and MIPS, which benefit from extensive community and industry backing.
Custom ISAs can be designed to ensure deterministic behavior and minimize undefined behaviors, which is crucial for the reliability and security of zkVMs. The focus on deterministic execution in custom ISAs aligns well with the need for verifiable, trustworthy zkVMs, making them particularly suitable for privacy-focused applications.
RISC-V offers a balanced approach, excelling in scalability and the potential for optimization. MIPS provides the stability and hardware availability that can be beneficial for mature, large-scale deployments. CAIRO, on the other hand, is specialized for ZK applications, providing a highly optimized platform for proof generation but at the cost of general-purpose flexibility. Custom ISAs like Lita's Valida take performance optimization even further by focusing exclusively on zkVM-specific operations, reducing computational overhead, and streamlining proof generation.
MIPS has the most robust hardware ecosystem due to its maturity, while RISC-V is catching up rapidly with significant community support and growing industry adoption. CAIRO lacks a comparable hardware base but compensates with its deep integration into ZK and blockchain ecosystems, making it an ideal choice for ZK-centric projects. Custom ISAs, while offering zk-specific optimizations, face challenges due to limited hardware and ecosystem support, requiring significant investment in custom tooling and hardware.
Both RISC-V and MIPS provide excellent support for high-level programming languages through established compiler toolchains such as GCC and LLVM. This support enables developers to compile languages like C, C++, and Rust, facilitating zkVM software development across both architectures. CAIRO, while optimized for ZK applications, lacks this broad compatibility with general-purpose high-level languages, focusing instead on its specialized ZK-centric tooling. Custom ISAs, by contrast, often require the development of specialized compiler toolchains, adding complexity to the development process.
RISC-V's formal specification and deterministic design make it attractive for zkVM implementations where reliability and verifiability are critical. However, practical deployment often involves a more extensive instruction set than the base ISA, complicating zkVM integration. The modularity of RISC-V, while advantageous for extensions, also results in a fragmented market, which can be a drawback for IoT applications where uniformity is essential.
Specialized ISAs, such as Lita's zk-optimized Valida, offer a different approach by minimizing unnecessary instructions and focusing explicitly on zkVM needs. This specialization can improve zkVM performance but lacks the versatility that RISC-V or MIPS can provide across different domains, particularly in non-blockchain applications.MIPS, with its established hardware ecosystem and stability, remains an attractive option for scenarios requiring reliability and support across both blockchain and non-blockchain environments. However, its lack of ZK-specific optimization means that it cannot always match the efficiency of custom ISAs for zk-specific tasks.
RISC-V, MIPS, CAIRO, and custom ISAs each bring unique strengths and weaknesses to zkVM implementations. RISC-V's open-source nature and scalability make it a flexible option for zkVMs, particularly where community innovation is key. MIPS provides stability, mature hardware support, and strong performance in established applications but lacks ZK-specific optimizations, such as is offered by a custom ISA. CAIRO stands out for its ZK-tailored architecture, offering streamlined proof generation for blockchain projects but limited in its general-purpose use. Custom ISAs, such as Lita's Valida, present the most zk-specific optimization, enhancing proof generation and reducing unnecessary complexity, but come with the trade-offs of requiring substantial development overhead and lacking a mature ecosystem.
Selecting the appropriate architecture for zkVMs depends on the specific requirements of the project, but each of these architectures can be argued as equally proficient for many applications, in which case the consideration of 'which zkVM' would be determined sheerly by other factors such as security and performance.
We have strived to be as accurate as possible with the above analysis. Should there be any need for corrections, please contact ben@hozk.io
