Editing Zilog Z8000 (section)

===Other features===
One uncommon feature found on the Z8000, more commonly associated with [[minicomputer]]s, is direct support for [[vectored interrupt]]s. Interrupts are used by external devices to notify the processor that some condition has been met; a common use is to indicate that data from a slow process like reading a [[floppy disk]] is now available and the CPU can read the data into memory.

Normally on small machines, an [[interrupt]] causes special code to run that examines various status bits and memory locations to decide what device actually called the interrupt and why. In some designs, especially those intended for [[realtime computing]], an area of memory is set aside as a set of pointers, or vectors, to the code handling a particular device. The devices causing the interrupt then set some state, typically via pins on the CPU, to indicate a particular interrupt number, N. When the interrupt is called, the CPU immediately jumps through Nth entry in the table, avoiding any need to decode the interrupt. This can greatly speed up the interrupt servicing by avoiding having to run additional operations, while also simplifying the interrupt handling code.

In the Z8000, a new register supports vectors, the Program Status Area Pointer. This was similar to a memory address in a register, consisting of two 16-bit values with the upper 16 bits holding the segment number in its upper 8 bits. The lower 16 bits are then divided in half, the upper 8 bits containing an offset and the lower 8 bits zeroed. To call a particular vector, the external device presents the lower 8 bits (or 9 in some cases) on the address/data bus, and the complete vector address is constructed from the three values.<ref name="abramovitz1981"/>{{rp|pages=6.8}}