implemented by simply combining the proper MSI circuits. Large Scale Integration (LSI) LSI circuits are large and complex, and generally contain circuitry equivalent to 100 or more typical logic gates. LSI circuits are also functional in nature. T y p i c a l  L S I  I C s  i n c l u d e  m e m o r i e s  a nd microprocessors. Very Large Scale Integration (VLSI) VLSI circuits are large, complex circuits that contain the equivalent of 1,000 or more logic gates. Early digital computers use a mix of SSI MSI, and LSI circuits. Over the years, the trend has been toward the greater use of MSI, LSI, and VLSI circuits. Today, most computers are predominately MSI, LSI, and VLSI circuits. The SSI circuits are used only in interfacing the other three larger and more sophisticated types. DIGITAL CIRCUIT CHARACTERISTICS Many factors influence the choice of logic circuits used to implement a digital computer. The most important of these are speed, power dissipation, and the availability of MSI, LSI, and VLSI circuits. Other factors include the cost, noise immunity, and interface capabilities. The most important choice of a type of logic involves speed and power dissipation. Speed refers to the frequency of operation or propagation delay of the logic circuits. The higher the speed of operation, the greater the amount of data that can be processed in a given time. Therefore, computer designers try to achieve as much speed as possible in their designs. Many high-speed circuits and techniques are available. Besides choosing circuits with low propagation delay times, circuit reduction techniques are used to minimize propagation delay through proper physical layout as well as logic simplification. However, speed is always obtained at the expense of increased power dissipation and cost. Invariably, the designer faces a speed-power tradeoff, and attempts to optimize the design for maximum speed within realistic power consumption and cost guidelines. Choosing ICs for use in a digital computer involves not only choosing a specific logic family, but also in choosing the correct mix of the various IC technologies available. By being flexible in the circuit choice of mix, a designer can more easily optimize the design. This means freely mixing different families of bipolar and MOS, as well as VLSI, LSI, MSI, and SSI circuits. For a detailed look at bipolar and MOS theory, as well as more information on VLSI, LSI, MSI, and SSI circuits, refer to Aviation Electronics Technician 2 (Intermediate), NAVEDTRA 12334, chapter 2. PROGRAMMING FUNDAMENTALS Learning Objective: Recognize concepts and procedures used in the construction of a computer program. Computer programming is the process of planning a solution to a problem. You can derive a general outline for calculating total resistance of a parallel resistance circuit by using the following steps: 1. Take the reciprocal of the resistance in ohms of all resistors in a circuit. 2. Calculate the sum of the values from step 1. 3. Compute the reciprocal of the value from step 2. The process of preparing a program from this explanation is not difficult. One basic charcteristic of the computer must be considered-it cannot think. It can only follow certain commands, which must be correctly expressed and must cover all possibilities. If a program is to be useful, it must be broken down into specifically defined operations or steps. These operations or steps, along with other data, must be communicated to the computer in a language that it can understand. NOTE: The instructions are read sequentially unless otherwise stated. Generally, the steps that a computer follows in the execution of a program are as follows: 1. Locates parameters (constants) and such data as necessary for problem solving 2. Transfers the parameter and data to the point of manipulation 3. Performs the manipulation according to certain rules of logic 8-13