Can separate functions be attained by hardware and software?

Do the subsystems of huge computer processes and programs still make sense when such processes and programs are broken down into their component parts? Why is it beneficial to divide the system in this way?

Why is it beneficial to have different logical systems and subsystems coexisting on a single computer?

What is computer ?               A computer is a digital electronic machine that can be programmed to carry out sequences of arithmetic or logical operations automatically. Modern computers can perform generic sets of operations known as programs. These programs enable computers to perform a wide range of tasks.