An Exception is an event (some synchronous; some asynchronous)
in the CPU that causes
it to change its normal flow of control.
Unfortunately, there is little consistency in the terms used
for exception systems.
The following table illustrates the problem:
| IBM | Intel | MIPS | Motorola | |
|---|---|---|---|---|
| Request service from the OS (e.g. to send text to the printer) |
Service Call (SVC) | Software Interrupt (INT) | System Call (SYSCALL) | TRAP |
| Unexcepted event in CPU (e.g. Programmer error; malfunction) |
Trap | Exception | Exception | Hardware Exception |
| I/O device request (e.g. Device signals I/O completion) |
Interrupt | External Interrupt | Interrupt | Interrupt |