Hardware and Computer Organization- P2

Hardware and Computer Organization- P2:Today, we often take for granted the impressive array of computing machinery that surrounds usand helps us manage our daily lives. Because you are studying computer architecture and digitalhardware, you no doubt have a good understanding of these machines, and you’ve probably writtencountless programs on your PCs and workstations.
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Hardware and Computer Organization- P2Chapter 1ever, according to Mann, a conversion factor of about 38 allows for a rough comparison. Thus,according to the published results7, a 1.0 GHz AMD Athlon processor achieved a SPECint95benchmark result of 42.9, which roughly compares to a SPECint92 result of 1630. The DigitalEquipment Corporation (DEC) AlphaStation 5/300 is one workstation that has published resultsfor both benchmark tests. It measures about 280 in the graph of Figure 1.6 and 7.33 according tothe SPECint95 benchmark. Multiplying by 38, we get 278.5, which is in reasonable agreementwith the earlier result. We’ll return to the issue of performance measurements in a later chapter.Number SystemsHow do you represent a number in computer? How do you send that number, whatever it maybe, a char, an int, a float or perhaps a double between the processor and memory, or withinthe microprocessor itself? This is a fair question to ask and the answer leads us naturally toan understanding of why modern digital computers are based on the binary (base 2) numbersystem. In order to investigate this, consider Figure 1.7.In Figure 1.7 we’ll do a simple-minded experiment.Let’s pretend that we can place an electrical voltage 24.56345 RADIOon the wire that represents the number we would SHACKlike to transmit between two functional elements ofthe computer. The method might work for simple 24.56345 Vnumbers, but I wouldn’t want to touch the wire if Iwas sending 2000.456! In fact, this method wouldbe extremely slow, expensive and would only workfor a narrow range of values. Direction of signalHowever, that doesn’t imply that this method isn’tused at all. In fact, one of the first families of elec- Zero voltstronic computers was the analog computer. The (ground)analog computer is based upon linear amplifiers,or the kind of electronic circuitry that you might Figure 1.7: Representing the value of afind in your stereo receiver at home. The key point number by the voltage on a wire.is that variables (in this case the voltages on wires)can assume an infinite range of values between some limits imposed by the nature of the circuitry.In many of the early analog computers this range might be between –25 volts and +25 volts. Thus,any quantity that could be represented as a steady, or time varying voltage within this range couldbe used as a variable within an analog computer.The analog computer takes advantage of the fact that there are electronic circuits that can do thefollowing mathematical operations: • Add / subtract • Log / anti-log • Multiply / divide • Differentiate / integrate 12 Introduction and Overview of Hardware ArchitectureBy combining this circuits one after another with intermediate amplification and scaling, real-timesystems could be easily modeled and the solution to complex linear differential equations could beobtained as the system was operating.However, the analog computer suffers from the samelimitations as does your stereo system. That is, itsamplification accuracy is not infinitely perfect, so the bestaccuracy that could be hoped for is about 0.01%, or about1 part in 10,000. Figure 1.8 shows an analog computerof the type used by the United States submarines duringWorld War II. The Torpedo Data Computer, or TDC,would take as its inputs the compass heading and speed ofthe target ship, the heading and speed of the submarine,the desired firing distance. The correct speed and headingwas then sent to the torpedoes and they would track thecourse, speed and depth transmitted to them by the TDC.Thus, within the limitations imposed by the electroniccircuitry of the 1940’s, an entire family of computers Figure 1.8: An analog computer from abased upon the idea of inputs and outputs based upon WWII submarine. Photo courtesy of www.continuous variables. In that sense, your stereo amplifier fleetsubmarine.com.is an analog computer. An amplifier amplifies, or boosts anelectrical signal. An amplifier with a gain of 10, hasan output voltage that is, at every instant of time, 10times greater than the input voltage. Thus, Vout = 10 4.2 RADIOVin. Here we have an analog computing block that SHACKhappens to be a multiplication block with a constantmultiplier. 2 4Anyway, let’s get back to discussing to number sys- 5 6tems. We might be able to improve on this method 3by breaking the number into more manageable parts 4 5and send a more limited signal range over severalwires at the same time (in parallel). Thus, each wire Zero volts (ground)would only need to transmit a narrow range of val-ues. Figure 1.9 shows how this might work. Figure 1.9: Using a parallel bundle of wires toIn this case, each wire in the bundle represents transmit a numeric value in a computer. Thea decimal decade and each number that we send wire’s position in the bundle det ...