Inside the Machine: An Illustrated Introduction to Microprocessors and Computer Architecture Read Online Free PDF

computer—it’s a computer in
    and of itself. Once you understand how this tiny computer works, you’ll have
    a thorough grasp of the fundamental concepts that underlie all of modern
    computing, from the aforementioned air traffic control system to the silicon
    brain that controls the brakes on a luxury car.
    This chapter will introduce you to the microprocessor, and you’ll begin
    to get a feel for just how straightforward computers really are. You need
    master only a few fundamental concepts before you explore the micro-
    processor technologies detailed in the later chapters of this book.
    To that end, this chapter builds the general conceptual framework on
    which I’ll hang the technical details covered in the rest of the book. Both
    newcomers to the study of computer architecture and more advanced readers
    are encouraged to read this chapter all the way through, because its abstrac-
    tions and generalizations furnish the large conceptual “boxes” in which I’ll
    later place the specifics of particular architectures.
    The Calculator Model of Computing
    Figure 1-1 is an abstract graphical representation of what a computer does.
    In a nutshell, a computer takes a stream of instructions (code) and a stream
    of data as input, and it produces a stream of results as output. For the pur-
    poses of our initial discussion, we can generalize by saying that the code stream consists of different types of arithmetic operations and the data stream consists of the data on which those operations operate. The results stream , then, is made up of the results of these operations. You could also say that the results
    stream begins to flow when the operators in the code stream are carried out
    on the operands in the data stream.
    Instructions
    Data
    Results
    Figure 1-1: A simple representation of
    a general-purpose computer
    NOTE
    Figure 1-1 is my own variation on the traditional way of representing a processor’s arithmetic logic unit (ALU) , which is the part of the processor that does the addition, subtraction, and so on, of numbers. However, instead of showing two operands entering the top ports and a result exiting the bottom port (as is the custom in the literature), I’ve depicted code and data streams entering the top ports and a results stream leaving the bottom port.
    2
    Chapter 1
    To illustrate this point, imagine that one of those little black boxes in the
    code stream of Figure 1-1 is an addition operator (a + sign) and that two of
    the white data boxes contain two integers to be added together, as shown in
    Figure 1-2.
    2
    +
    3
    =
    5
    Figure 1-2: Instructions are combined
    with data to produce results
    You might think of these black-and-white boxes as the keys on a
    calculator—with the white keys being numbers and the black keys being
    operators—the gray boxes are the results that appear on the calculator’s
    screen. Thus the two input streams (the code stream and the data stream)
    represent sequences of key presses (arithmetic operator keys and number
    keys), while the output stream represents the resulting sequence of numbers
    displayed on the calculator’s screen.
    The kind of simple calculation described above represents the sort of
    thing that we intuitively think computers do: like a pocket calculator, the
    computer takes numbers and arithmetic operators (such as +, –, ÷, ×, etc.) as
    input, performs the requested operation, and then displays the results. These
    results might be in the form of pixel values that make up a rendered scene in a
    computer game, or they might be dollar values in a financial spreadsheet.
    The File-Clerk Model of Computing
    The “calculator” model of computing, while useful in many respects, isn’t the
    only or even the best way to think about what computers do. As an alterna-
    tive, consider the following definition of a computer:
    A computer is a device that shuffles numbers around from place to
    place, reading, writing, erasing, and rewriting different numbers