Quality of Service (QoS) is a generic term that normally refers to the ability of a network or other entity (in our case, PCI Express) to provide predictable latency and bandwidth. QoS is of particular interest when applications require guaranteed bus bandwidth at regular intervals, such as audio data. To help deal with this type of requirement PCI Express defines isochronous transactions that require a high degree of QoS. However, QoS can apply to any transaction or series of transactions that must traverse the PCI Express fabric. Note that QoS can only be supported when the system and device-specific software is PCI Express aware.
QoS can involve many elements of performance including:
Effective Bandwidth ...