computer architecture :: essays papers

computer architecture Computer architecture covers the design of system software, such as the operating system (the program that controls the computer), as well as referring to the combination of hardware and basic software that links the machines on a computer network. Computer architecture refers to an entire structure and to the details needed to make it functional. Thus, computer architecture covers computer systems, microprocessors, circuits, and system programs. Typically the term does not refer to application programs, such as spreadsheets or word processing, which are required to perform a task but not to make the system run. In designing a computer system, architects consider five major elements that make up the system's hardware: the arithmetic/logic unit, control unit, memory, input, and output. The arithmetic/logic unit performs arithmetic and compares numerical values. The control unit directs the operation of the computer by taking the user instructions and transforming them into electrical signals that the computer's circuitry can understand. The combination of the arithmetic/logic unit and the control unit is called the central processing unit (CPU). The memory stores instructions and data. The input and output sections allow the computer to receive and send data, respectively. Different hardware architectures are required because of the specialized needs of systems and users. One user may need a system to display graphics extremely fast, while another system may have to be optimized for searching a database or conserving battery power in a laptop computer. In addition to the hardware design, the architects must consider what software programs will operate the system. Software, such as programming languages and operating systems, makes the details of the hardware architecture invisible to the user. For example, computers that use the C programming language or a UNIX operating system may appear the same from the user's viewpoint, although they use different hardware architectures. When a computer carries out an instruction, it proceeds through five steps. First, the control unit retrieves the instruction from memory—for example, an instruction to add two numbers. Second, the control unit decodes the instructions into electronic signals that control the computer. Third, the control unit fetches the data (the two numbers). Fourth, the arithmetic/logic unit performs the specific operation (the addition of the two numbers). Fifth, the control unit saves the result (the sum of the two numbers). Early computers used only simple instructions because the cost of electronics capable of carrying out complex instructions was high. As this cost decreased in the 1960s, more complicated instructions became possible. Complex instructions can save time because they make it unnecessary for the computer to retrieve additional instructions. For example, if seven operations are combined in one instruction, then six of