Real-time scheduling means that an application receives a fixed amount of data in a fixed length of time. The data can be returned at any time during the time quantum. This type of reservation is used by applications that do only a small amount of buffering. If the application requests more data than its rate guarantee, the system suspends the application until it falls within the guaranteed bandwidth.
Deadline scheduling means that an application receives a minimum amount of data in a fixed length of time. Such guarantees are used by applications that have a large amount of buffer space. The application requests I/O at a rate at least as fast as the rate guarantee and is suspended only when it is exceeding its rate guarantee and there is no additional device bandwidth available.
Nonscheduled reservations means that the guarantee received by the application is only a reservation of system bandwidth. The system does not enforce the reservation limits and therefore cannot guarantee the I/O rate of any of the guarantees on the system. Nonscheduled reservations should be used with extreme care.