The process group approach to reliable distributed computing, as discussed in this article, addresses the challenge of building reliable distributed systems by leveraging process groups and group programming tools. Unlike traditional distributed systems that focus on communication performance, the ISIS system emphasizes the need for tools that ensure reliability through process groups. The thesis of ISIS is that reliable distributed software can be simplified by using process groups and group programming tools. ISIS is designed to support the construction of reliable distributed software by providing tools for managing process groups, including group communication, synchronization, and fault tolerance. The system is particularly useful in environments where reliability is critical, such as trading systems, where accurate and timely information is essential. These systems must serve multiple communities, including the firm, brokers, and system administrators, each with different requirements for reliability, speed, and customization. The article discusses the challenges of building reliable distributed systems, including the need for predictable and fault-tolerant behavior, the management of group membership, and the handling of message delivery ordering. It also highlights the importance of addressing these issues through a unified framework, such as the virtual synchrony execution model, which allows for asynchronous execution while maintaining the necessary order of events. The ISIS system provides a range of tools for managing process groups, including creating and deleting groups, multicast communication, synchronization, replicated data, monitoring, and automated recovery. These tools are essential for building reliable distributed systems, particularly in environments where the system must handle high volumes of data and maintain consistency across multiple processes. The article also discusses the challenges of conventional message-passing technologies, including the limitations of unreliable datagrams, remote procedure calls, and reliable data streams. It highlights the need for a more robust approach to communication that can handle failures and ensure reliable message delivery. In conclusion, the process group approach to reliable distributed computing, as exemplified by the ISIS system, provides a framework for building reliable distributed systems by leveraging process groups and group programming tools. This approach addresses the challenges of communication reliability, group membership management, and message delivery ordering, making it particularly suitable for applications where reliability is critical.The process group approach to reliable distributed computing, as discussed in this article, addresses the challenge of building reliable distributed systems by leveraging process groups and group programming tools. Unlike traditional distributed systems that focus on communication performance, the ISIS system emphasizes the need for tools that ensure reliability through process groups. The thesis of ISIS is that reliable distributed software can be simplified by using process groups and group programming tools. ISIS is designed to support the construction of reliable distributed software by providing tools for managing process groups, including group communication, synchronization, and fault tolerance. The system is particularly useful in environments where reliability is critical, such as trading systems, where accurate and timely information is essential. These systems must serve multiple communities, including the firm, brokers, and system administrators, each with different requirements for reliability, speed, and customization. The article discusses the challenges of building reliable distributed systems, including the need for predictable and fault-tolerant behavior, the management of group membership, and the handling of message delivery ordering. It also highlights the importance of addressing these issues through a unified framework, such as the virtual synchrony execution model, which allows for asynchronous execution while maintaining the necessary order of events. The ISIS system provides a range of tools for managing process groups, including creating and deleting groups, multicast communication, synchronization, replicated data, monitoring, and automated recovery. These tools are essential for building reliable distributed systems, particularly in environments where the system must handle high volumes of data and maintain consistency across multiple processes. The article also discusses the challenges of conventional message-passing technologies, including the limitations of unreliable datagrams, remote procedure calls, and reliable data streams. It highlights the need for a more robust approach to communication that can handle failures and ensure reliable message delivery. In conclusion, the process group approach to reliable distributed computing, as exemplified by the ISIS system, provides a framework for building reliable distributed systems by leveraging process groups and group programming tools. This approach addresses the challenges of communication reliability, group membership management, and message delivery ordering, making it particularly suitable for applications where reliability is critical.