If we only think of i/O devices that are used for storage, for example, they are designed for permanence. When the power is shut off, they don’t forget what they are storing. But CPUs are designed for rapid change without permanence. A significant change happens on every CPU cycle. The bits in a CPU don’t need to retain their state for years; they’ll switch to a different state in the next microsecond anyway.

In between I/O and CPU are other elements such as memory and cache. The characteristics of all of them are a balance between what’s needed for a particular degree of permanence and a degree of switching speed. Micro-components that switch states extremely fast are not so good at retaining data.

Then there is distance. I/O devices tend to be farther away. The distance between L3 cache and actual logic units can be within the millimeter range, while a signal from an I/O device may be many centimeters away, or even meters. As fast as signals can travel, it still takes ten or a hundred times longer to travel ten or a hundred times as far.

And an I/O device generally doesn’t do anything until a CPU has processed instructions that result in a signal being sent to the I/O device. Most things done by an I/O device necessarily require some interaction through the CPU before and after the I/O device completes the request.

There are lots of reasons. But about the only useful answer is because they’re designed and intended to do different things.

Tom

It is a physical device that reads the punch card (or the paper tape) and translates it to electronic form.