I think the market has splintered a little bit, low-latency &quot;real-time&quot; stuff tends to be targeted more by simpler devices, whereas the GHz SOCs and DSPs are more often used for heavy number-crunching or &quot;less real-time&quot; applications where they may be running a full OS. Some of the delay is probably due to hardware support for things like scheduling, multi-threading etc.<p>As for current tech that can match the Z80, I know the MSP430 can have an interrupt latency of about 10 cycles. This can be below 1us with the kind of clock speeds many of the parts will run at.<p>Apparently (according to the manual) an ARM Cortex M3 can enter an interrupt in 12 cycles. This can be much faster as the parts can be run above 100MHz.