The explosive advent of the blockchain technology has led to hundreds of blockchain systems in the industry, thousands of academic papers published over the last few years, and an even larger number of new initiatives and projects. Despite the emerging consolidation efforts, the area remains highly turbulent without systematization, educational materials, or cross-system comparative analysis.

In this paper, we provide a systematic and comprehensive study of four popular yet widely different blockchain systems: Bitcoin, Ethereum, Hyperledger Fabric, and IOTA. The study is presented as a cross-system comparison, which is organized by clearly identified aspects: definitions, roles of the participants, entities, and the characteristics and design of each of the commonly used layers in the cross-system blockchain architecture. Our exploration goes deeper compared to what is currently available in academic surveys and tutorials. For example, we provide the first extensive coverage of the storage layer in Ethereum and the most comprehensive explanation of the consensus protocol in IOTA. The exposition is due to the consolidation of fragmented information gathered from white and yellow papers, academic publications, blogs, developer documentation, communication with the developers, as well as additional analysis gleaned from the source code. We hope that this survey will help the readers gain in-depth understanding of the design principles behind blockchain systems and contribute towards systematization of the area.

区块链技术的爆炸性出现导致行业内出现了数百个区块链系统，过去几年发表了数千篇学术论文，以及更多的新举措和项目。尽管不断出现整合努力，但由于缺乏系统化、教育材料或跨系统比较分析，该领域仍然高度动荡。

在本文中，我们对四种流行但又截然不同的区块链系统进行了系统而全面的研究：比特币、以太坊、Hyperledger Fabric 和 IOTA。该研究以跨系统比较的形式呈现，由明确确定的方面组成：定义、参与者的角色、实体以及跨系统区块链架构中每个常用层的特征和设计。与目前学术调查和教程中提供的内容相比，我们的探索更加深入。例如，我们首次对以太坊的存储层进行了广泛的覆盖，对IOTA的共识协议进行了最全面的解释。展览是由于整合了从白皮书和黄皮书、学术出版物、博客、开发人员文档、与开发人员的沟通以及从源代码中收集的其他分析。我们希望本次调查能够帮助读者深入了解区块链系统背后的设计原理，并为该领域的系统化做出贡献。