Back then, transistors were a form of component, but they were very limited and simple. You could build a small scale electronic system, but i t wasn't scalable, and it was primitive. There's a strong analogy between what happened then in hardware and what is happening now in software. It was hard to use these technologies to create building blocks with well-defined interfaces that could be reused easily. Component-based development takes object technology to a higher level.
Components build upon the object building block.
Components tend to go beyond individual objects. A whole billing subsystem for a cell phone com pany, which could have hundreds of separate objects in it, can be a component. Modules that sit on top of a core database are another example of components. What's happening now is components are getting standardized. Using the hardware example again, there's only one notation used to design electronic circuits, shared by all circuit designers in the world.