trap, exception, fault, interrupt, abort

Some material is very old and may be incorrect today

© August 2004 Tony Lawrence

Computers screw up. You can have meaningless instructions, attempts to divide by zero, attempts to access non-existent memory, and other situations the cpu can't deal with. These are all similar events, and some are used interchangeably at times. There are subtle differences in what these specifically mean, but there is also a lot of overlap.

First, consider the mechanics: if we have a problem (like division by zero or a bad memory reference), we need both code to handle the problem and a way to get to that code. Handling might mean printing an informative warning message, silently allocating memory for a process that needs it,killing off an errant process, or even shutting down the entire machine. The way to get to the handler is going to be through some sort of vector table: if you have problem number 0, jump to this code, and so on.

So all these things are really interrupts to normal CPU instruction flow. If we want to be precise, we can say that "interrupts" come from outside the cpu's hardware (some other device requesting attention or program code requesting a software interrupt), a "fault" happens before the CPU can execute the instruction (divide by zero, bogus instruction), a trap happens after or during the execution (a debugger breakpoint, an overflow situation), and an "abort" is something where the CU has no idea what is going on at all.

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