Interrupts and Buffers.

What is an interrupt?
An interrupt is a signal from a device attached to a computer or from a program within the computer that requires the operating system to stop and figure out what to do next.

Examples: 

• A signal to stop Microsoft Word so that a PowerPoint presentation can gear up.
• When a key is pressed or when the mouse is moved.
• When communicating with the disk controller for reading and writing data to and from a disk.

Steps an interrupt follows.

• Interrupt is raised
• Current CPU instruction is completed
• Contents of internal registers are stored in (pushed onto) the stack.
• The memory address of the ISR(Interrupt Service Routine) is found and transfer controlled.
• ISR is run
• Internal register contents are restored (popped) from the stack
• Original process continues from where it was stopped.

What is a buffer?

A buffer is a data area shared by hardware devices or program processes that operate at different speeds or with different sets of priorities. 

Why is it important?

The purpose of a buffer is to hold data right before it is used. For example, when you download an audio or video file from the Internet, it may load the first 20% of it into a buffer and then begin to play. While the clip plays back, the computer continually downloads the rest of the clip and stores it in the buffer.