In this method for interrupts all I/O modules share a common interrupt request lines. However the interrupt acknowledge line is connected in a daisy chain fashion. When the processor senses an interrupt, it sends out an interrupt acknowledgement.

The interrupt acknowledge signal propagates through a series of I/O module until it gets to a requesting module.

The requesting module typically responds by placing a word on the data lines. This word is referred to as a vector and is either the address of the I/O module or some other unique identification.

In either case, the processor uses the vector as a pointer to the appropriate device service routine. This avoids the need to execute a general interrupt service routine first. This technique is referred to as a vectored interrupt. The daisy chain arrangement is shown in the Figure 6.7.

Figure 6.7: Daisy chain arrangement