Pipelining: Basic and Intermediate Concepts - Computer Architecture: A Quantitative Approach - page 660

FIGURE C.30 The names of common exceptions vary across four different architec-
tures . Every event on the IBM 360 and 80×86 is called an interrupt , while every event on the
680×0 is called an exception . VAX divides events into interrupts or exceptions. The adjectives
device, software , and urgent are used with VAX interrupts, whereas VAX exceptions are sub-
divided into faults, traps , and aborts.
Although we use the term exception to cover all of these events, individual events have im-
portant characteristics that determine what action is needed in the hardware. The require-
ments on exceptions can be characterized on five semi-independent axes:
1. Synchronous versus asynchronous —If the event occurs at the same place every time the pro-
gram is executed with the same data and memory allocation, the event is synchronous . With
the exception of hardware malfunctions, asynchronous events are caused by devices extern-
all to the CPU and memory. Asynchronous events usually can be handled after the comple-
tion of the current instruction, which makes them easier to handle.
2. User requested versus coerced —If the user task directly asks for it, it is a user-requested event.
In some sense, user-requested exceptions are not really exceptions, since they are predict-