Asynchronous logic is the logic required for the design of asynchronous digital systems. Digital sequential logic circuits are divided into synchronous and asynchronous types. Standby servers can be synchronous or asynchronous. Synchronization primitives may be used to have synchronous behavior with an asynchronous IPC mechanism. HDLC frames can be transmitted over synchronous or asynchronous serial communication links. AC electric motors are either asynchronous or synchronous. Synchronous communication can be built on top of asynchronous communication by using a Synchronizer. The Runspace then must be opened for either synchronous processing or asynchronous processing. Both synchronous and asynchronous transmissions are supported by the standard. Groupware is a combination of synchronous, asynchronous and community focused tools. ATR under asynchronous and synchronous transmission have entirely different form and content. The consensus problem may be considered in the case of asynchronous or synchronous systems. The problem has been studied in the case of both synchronous and asynchronous communications. IEEE 1394 fully supports both isochronous and asynchronous applications. Program flow using asynchronous XHR callbacks can present difficulty with readability and maintenance.