Code: The Hidden Language of Computer Hardware and Software, 2nd Edition

Chapter Twenty-One

The Arithmetic Logic Unit

The modern computer is a complex assemblage of myriad components, but they can roughly be divided into three categories:

• Memory

• The central processing unit, or CPU

• Input and output (I/O) devices, often called peripherals

You learned in Chapter 19 how random-access memory is constructed and structured and how each byte in memory is accessed through an address. In Chapter 20 you saw how the contents of memory can store numbers and how codes stored in memory can control circuitry that manipulates these numbers. In the more general case, the contents of memory can also contain text, pictures, music, movies, and anything else that can be represented digitally—that is, with 0s and 1s. The instruction ...