IGCSE Computer Science Paper 1 Definitions Worksheet: 4.1 Types of Software and Interrupts (Modules 409–418)
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Key terms
Write what each term means, in your own words.
1
interrupt source
2
interrupt signal
3
interrupt check
4
interrupt priority
5
interrupt service routine (ISR)
6
save register contents
7
interrupt outcome
8
interrupt handling sequence
9
OS interrupt handling
10
point and reason
Answer Key
IGCSE Computer Science Paper 1 · Modules 409–418 · Student wording will vary for definitions
1interrupt source — The origin of the signal. From a device, like a key press or mouse move, it is a hardware interrupt. From a running program, like divide by zero or a memory clash, it is a software interrupt.
2interrupt signal — A signal sent to the CPU by a device (hardware) or a running program (software) when an event, such as a key press, needs the CPU's attention.
3interrupt check — At the end of each fetch-decode-execute cycle the CPU checks for an interrupt signal. If none, it fetches the next instruction; if one, it switches to handling it first.
4interrupt priority — Each interrupt has a priority level. The CPU handles the most urgent one first, so a power failure can pause the handling of a less urgent key press.
5interrupt service routine (ISR) — A small program the CPU runs to deal with one particular interrupt. Each type of interrupt has its own ISR, kept in memory, and it is short so the CPU can quickly return to its task.
6save register contents — Before running the ISR, the CPU stores its register contents, including the program counter, so the interrupted task can later carry on exactly where it stopped.
7interrupt outcome — What the ISR does depends on the event: it reads a key press, updates the pointer, shows an error or stops a faulty program. Then the CPU resumes the task it was running.
8interrupt handling sequence — The ordered steps: an interrupt is generated, the CPU finishes its cycle and detects it, saves its state, runs the ISR, restores its state, then resumes the original task.
9OS interrupt handling — The OS receives each interrupt, picks the right ISR to run, manages priorities, then passes control back to the interrupted program so it can carry on.
10point and reason — A full-mark answer uses the correct terms (system software, firmware, bootloader, ISR), gives points in the right order, and adds a reason for each point.