What Is the Difference Between Trap and Interrupt?
If the Terminology Is Different for Different Systems, Then What Do They Mean on X86? 10 Answers a Trap Is an Exception in a User Process. It's Caused by...
What is the difference between Trap and Interrupt?
If the terminology is different for different systems, then what do they mean on x86?
10 Answers
A trap is an exception in a user process. It's caused by division by zero or invalid memory access. It's also the usual way to invoke a kernel routine (a system call) because those run with a higher priority than user code. Handling is synchronous (so the user code is suspended and continues afterwards). In a sense they are "active" - most of the time, the code expects the trap to happen and relies on this fact.
An interrupt is something generated by the hardware (devices like the hard disk, graphics card, I/O ports, etc). These are asynchronous (i.e. they don't happen at predictable places in the user code) or "passive" since the interrupt handler has to wait for them to happen eventually.
You can also see a trap as a kind of CPU-internal interrupt since the handler for trap handler looks like an interrupt handler (registers and stack pointers are saved, there is a context switch, execution can resume in some cases where it left off).
Traps and interrupts are closely related. Traps are a type of exception, and exceptions are similar to interrupts.
Intel x86 defines two overlapping categories, vectored events (interrupts vs exceptions), and exception classes (faults vs traps vs aborts).
All of the quotes in this post are from the April 2016 version of the Intel Software Developer Manual. For the (definitive and complex) x86 perspective, I recommend reading the SDM's chapter on Interrupt and Exception handling.
Vectored Events
Vectored Events (interrupts and exceptions) cause the processor to jump into an interrupt handler after saving much of the processor's state (enough such that execution can continue from that point later).
Exceptions and interrupts have an ID, called a vector, that determines which interrupt handler the processor jumps to. Interrupt handlers are described within the Interrupt Descriptor Table.
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Interrupts
Interrupts occur at random times during the execution of a program, in response to signals from hardware. System hardware uses interrupts to handle events external to the processor, such as requests to service peripheral devices. Software can also generate interrupts by executing the INT n instruction.
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