What is the difference between Trap and Interrupt?

Question

What is the difference between Trap and Interrupt?

If the terminology is different for different systems, then what do they mean on x86?

Answer 1

I think Traps are caused by the execution of current instruction and thus they are called as synchronous events. where as interrupts are caused by an independent instruction that is running in the processor which are related to external events and thus are known as asynchronous ones.

Answer 2

Generally speaking, terms like exceptions, faults, aborts, Traps, and Interrupts all mean the same thing and are called "Interrupts".

Coming to the difference between Trap and Interrupt:

Trap: Is a programmer initiated and expected transfer of control to a special handler routine. (For ex: 80x86 INT instruction is a good example)

Where as

Interrupt(Hardware): Is a program control interruption based on an external hardware event external to the CPU (For ex: Pressing a key on the keyboard or a time out on a timer chip)

Answer 3

A trap is called by code like programs and used e. g. to call OS routines (i. e. normally synchronous). An interrupt is called by events (many times hardware, like the network card having received data, or the CPU timer), and - as the name suggests - interrupts the normal control flow, as the CPU has to switch to the driver routine to handle the event.

Answer 4

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).

Answer 5

A Trap can be identified as a transfer of control, which is initiated by the programmer. The term Trap is used interchangeably with the term Exception (which is an automatically occurring software interrupt). But some may argue that a trap is simply a special subroutine call. So they fall in to the category of software-invoked interrupts. For example, in 80×86 machines, a programmer can use the int instruction to initiate a trap. Because a trap is always unconditional the control will always be transferred to the subroutine associated with the trap. The exact instruction, which invokes the routine for handling the trap is easily identified because an explicit instruction is used to specify a trap.

Answer 6

Interrupts are hardware interrupts, while traps are software-invoked interrupts. Occurrences of hardware interrupts usually disable other hardware interrupts, but this is not true for traps. If you need to disallow hardware interrupts until a trap is served, you need to explicitly clear the interrupt flag. And usually the interrupt flag on the computer affects (hardware) interrupts as opposed to traps. This means that clearing this flag will not prevent traps. Unlike traps, interrupts should preserve the previous state of the CPU.