> nearly universally available on 8-bit micros, much less 16, but I have also wondered before how important they really were for what those machines ended up be

> nearly universally available on 8-bit micros, much less 16, but I have also wondered before how important they really were for what those machines ended up being used for Usually available, yes. But not all that widely used by those systems. The stock Apple II for example, has nothing in it that can even generate an interrupt. You'd have to install an expansion card. The standard serial cards can generate an interrupt upon character receipt for example, but they were usually programmed with polled IO anyway. Later with network cards and hard disks, you do see some use of interrupts. > On the other hand, though, the vertical blank interrupt was pretty critical to their software The Atari 2600 had no hardware interrupt support at all. You could tell the graphics IC to sleep the CPU until the next scanline. You'd turn vblank on, generate 3 lines of vblank, then turn vblank off. You'd be lined up with vblank from that point if you counted carefully. On an in-order-execution processor, most things can in principle be translated into periodic polling and cycle counting. But it involves some extraordinarily painful coding. A timer and an interrupt are quite a relief when you're doing something time-sensitive.