Inside and around the CPU


  •  Inside and around the CPU

    In this and the following chapters, I will focus on a detailed look at the CPU. One of the goals is help to you understand why manufacturers keep releasing new and more powerful processors. In order to explain that, we will have to go through what will at times be a quite detailed analysis of the CPU’s inner workings.
    Some of the chapters will probably be fairly hard to understand; I have spent a lot of time myself on my “research”, but I hope that what I present in these chapters will shed some light on these topics.
    Naturally, I will spend most of my time on the latest processors (the Athlon XP and Pentium 4). But we need to examine their internal architectures in light of the older CPU architectures, if we want to understand them properly. For this reason I will continually make comparisons across the various generations of CPU’s.
    I will now take you on a trip inside the CPU. We will start by looking at how companies like Intel and AMD can continue to develop faster processors.

    Two ways to greater speed

    Of course faster CPU’s are developed as a result of hard work and lots of research. But there are two quite different directions in this work:

  • More power and speed in the CPU, for example, from higher clock frequencies.

  • Better exploitation of existing processor power.
    Both approaches are used. It is a well-known fact that bottlenecks of various types drain the CPU of up to 75 % of its power. So if these can be removed or reduced, the PC can become significantly faster without having to raise the clock frequency dramatically.
    It’s just that it is very complicated to remove, for example, the bottleneck surrounding the front side bus, which I will show you later. So the manufacturers are forced to continue to raise the working rate (clock frequency), and hence to develop new process technology, so that CPU’s with more power can come onto the market.

    Clock frequencies

    If we look at a CPU, the first thing we notice is the clock frequency. All CPU’s have a working speed, which is regulated by a tiny crystal.
    The crystal is constantly vibrating at a very large number of “beats” per second. For each clock tick, an impulse is sent to the CPU, and each pulse can, in principle, cause the CPU to perform one (or more) actions.
    Fig.  54. The CPU’s working speed is regulated by a crystal which “oscillates” millions of times each second.
    The number of clock ticks per second is measured in Hertz. Since the CPU’s crystal vibrates millions of times each second, the clock speed is measured in millions of oscillations (megahertz or MHz). Modern CPU’s actually have clock speeds running into billions of ticks per second, so we have started having to use gigahertz (GHz).
    These are unbelievable speeds. See for yourself how short the period of time is between individual clock ticks at these frequencies. We are talking about billionths of a second:
    Clock frequency
    Time period per clock tick
    133 MHz
    0.000 000 008 000 seconds
    1200 MHz
    0.000 000 000 830 seconds
    2 GHz
    0.000 000 000 500 seconds

    Fig.  55. The CPU works at an incredible speed.
    The trend is towards ever increasing clock frequencies. Let’s take a closer look at how this is possible.

    More transistors

    New types of processors are constantly being developed, for which the clock frequency keeps getting pushed up a notch. The original PC from 1981 worked at a modest 4.77 MHz, whereas the clock frequency 20 years later was up to 2 GHz.
    In Fig. 56 you can see an overview of the last 20 years of development in this area. The table shows the sevengenerations of Intel processors which have brought about the PC revolution. The latest version of Pentium 4 is known under the code name Prescott.
    Gen.
    CPU
    Yr
    (intr.)
    Clock
    Frequency
    No. of
    transistors
    1
    8088
    1979
    4.77- 8 MHz
    29,000
    2
    80286
    1982
    6-12.5 MHz
    134,000
    3
    80386
    1985
    16-33 MHz
    275,000
    4
    80486
    1989
    25-100 MHz
    1,200,000
    5
    Pentium
    Pentium MMX
    1993
    1997
    60-200 MHz
    166-300 MHz
    3,100,000
    4,500,000
    6
    Pentium Pro
    Pentium II
    Pentium III
    1995
    1997
    1999
    150-200 MHz
    233-450 MHz
    450-1200 MHz
    5,500,000
    7,500,000
    28,000,000
    7
    Pentium 4


    “Prescott“
    2000
    2002
    2003
    2004
    1400-2200
    2200-2800
    2600-3200
    2800-3600
    42,000,000
    55,000,000
    55,000,000
    125,000,000

    Fig.  56. Seven generations of CPU’s from Intel. The number of transistors in the Pentium III and 4 includes the L2 cache.
    Each processor has been on the market for several years, during which time the clock frequency has increased. Some of the processors were later released in improved versions with higher clock frequencies, I haven’t included the Celeron in the overview processor. Celerons are specially discount versions of the Pentium II, III, and 4 processors.
    Anyone can see that there has been an unbelievable development. Modern CPU’s are one thousand times more powerful than the very first ones.
    In order for the industry to be able to develop faster CPU’s each year, new manufacturing methods are required.More and more transistors have to be squeezed into smaller and smaller chips.
    Fig.  57.
    A photograph from one of Intel’s factories, in which a technician displays the Pentium 4 processor core. It is a tiny piece of silicon which contains 42 million transistors.
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