Virtual time is a new paradigm for organizing and synchronizing distributed systems, applicable to problems like distributed discrete event simulation and database concurrency control. It provides a flexible abstraction of real time, similar to how virtual memory abstracts real memory. Implemented via the Time Warp mechanism, which uses lookahead-rollback and antimessages for synchronization. Virtual time is a global, one-dimensional temporal coordinate system used to measure progress and define synchronization. It may or may not relate to real time, and is used to ensure causality and order in distributed systems. Virtual time systems are subject to two fundamental rules: the virtual send time of a message must be less than its receive time, and the virtual time of an event must be less than the next event in the same process. These rules are similar to Lamport's Clock Conditions. Virtual time systems differ in various dimensions, such as being discrete or continuous, partially or totally ordered, and whether they are related to real time. Virtual time systems can be implemented with or without explicit manipulation by programmers. The Time Warp mechanism is an inverse of Lamport's algorithm, assigning global temporal coordinates to events. It allows processes to roll back to earlier virtual times when conflicts arise, ensuring correct execution. The mechanism is efficient and scalable, handling rollback and antimessages to maintain correctness. Virtual time systems are compared to other artificial time scales, such as pseudotime and Schneider's synchronization mechanisms. The Time Warp mechanism is efficient and scalable, handling rollback and antimessages to maintain correctness. It is used in distributed systems for synchronization and concurrency control, and has been applied to distributed simulation and database systems. Virtual time systems are subject to global virtual time (GVT), which is a property of a system's state at a given real time. GVT is used for global control, memory management, and flow control. Virtual time systems have been applied to distributed simulation and database concurrency control, with examples showing their effectiveness. Virtual time is a flexible abstraction of real time, used to organize and synchronize distributed systems. It is implemented via the Time Warp mechanism, which uses lookahead-rollback and antimessages for synchronization. Virtual time systems are subject to two fundamental rules and are used in various applications, including distributed simulation and database concurrency control. The Time Warp mechanism is efficient and scalable, handling rollback and antimessages to maintain correctness. Virtual time systems are compared to other artificial time scales, such as pseudotime and Schneider's synchronization mechanisms. The Time Warp mechanism is efficient and scalable, handling rollback and antimessages to maintain correctness. Virtual time systems are used in distributed systems for synchronization and concurrency control, and have been applied to distributed simulation and database systems. Virtual time is a flexible abstraction of real time, used to organize and synchronize distributed systems. It is implemented via the Time Warp mechanism, which uses lookahead-rollback and antimessages for synchronization. Virtual time systems are subject to two fundamental rules and are used in various applications, including distributed simulation and database concurrency control. The Time Warp mechanism is efficient andVirtual time is a new paradigm for organizing and synchronizing distributed systems, applicable to problems like distributed discrete event simulation and database concurrency control. It provides a flexible abstraction of real time, similar to how virtual memory abstracts real memory. Implemented via the Time Warp mechanism, which uses lookahead-rollback and antimessages for synchronization. Virtual time is a global, one-dimensional temporal coordinate system used to measure progress and define synchronization. It may or may not relate to real time, and is used to ensure causality and order in distributed systems. Virtual time systems are subject to two fundamental rules: the virtual send time of a message must be less than its receive time, and the virtual time of an event must be less than the next event in the same process. These rules are similar to Lamport's Clock Conditions. Virtual time systems differ in various dimensions, such as being discrete or continuous, partially or totally ordered, and whether they are related to real time. Virtual time systems can be implemented with or without explicit manipulation by programmers. The Time Warp mechanism is an inverse of Lamport's algorithm, assigning global temporal coordinates to events. It allows processes to roll back to earlier virtual times when conflicts arise, ensuring correct execution. The mechanism is efficient and scalable, handling rollback and antimessages to maintain correctness. Virtual time systems are compared to other artificial time scales, such as pseudotime and Schneider's synchronization mechanisms. The Time Warp mechanism is efficient and scalable, handling rollback and antimessages to maintain correctness. It is used in distributed systems for synchronization and concurrency control, and has been applied to distributed simulation and database systems. Virtual time systems are subject to global virtual time (GVT), which is a property of a system's state at a given real time. GVT is used for global control, memory management, and flow control. Virtual time systems have been applied to distributed simulation and database concurrency control, with examples showing their effectiveness. Virtual time is a flexible abstraction of real time, used to organize and synchronize distributed systems. It is implemented via the Time Warp mechanism, which uses lookahead-rollback and antimessages for synchronization. Virtual time systems are subject to two fundamental rules and are used in various applications, including distributed simulation and database concurrency control. The Time Warp mechanism is efficient and scalable, handling rollback and antimessages to maintain correctness. Virtual time systems are compared to other artificial time scales, such as pseudotime and Schneider's synchronization mechanisms. The Time Warp mechanism is efficient and scalable, handling rollback and antimessages to maintain correctness. Virtual time systems are used in distributed systems for synchronization and concurrency control, and have been applied to distributed simulation and database systems. Virtual time is a flexible abstraction of real time, used to organize and synchronize distributed systems. It is implemented via the Time Warp mechanism, which uses lookahead-rollback and antimessages for synchronization. Virtual time systems are subject to two fundamental rules and are used in various applications, including distributed simulation and database concurrency control. The Time Warp mechanism is efficient and