Computers that combine several instructions into a single operation are called complex instruction set computers (CISC). For example, if seven operations are combined in one instruction, then six of the steps that fetch instructions are eliminated and the computer spends less time processing that operation. Complex instructions (single instructions that specify multiple operations) can save time because they make it unnecessary for the computer to retrieve additional instructions. As this cost decreased in the 1960s, more complicated instructions became possible. Fifth, the control unit saves the result (the sum of the two numbers).Įarly computers used only simple instructions because the cost of electronics capable of carrying out complex instructions was high. Fourth, the arithmetic/logic unit performs the specific operation (the addition of the two numbers). Third, the control unit fetches the data (the two numbers). Second, the control unit decodes the instructions into electronic signals that control the computer. First, the control unit retrieves the instruction from memoryfor example, an instruction to add two numbers.
When a computer carries out an instruction, it proceeds through five steps. 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. Software, such as programming languages and operating systems, makes the details of the hardware architecture invisible to the user.
#Computer programs for architecture software#
In addition to the hardware design, the architects must consider what software programs will operate the system. 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. The input and output sections allow the computer to receive and send data, respectively.ĭifferent hardware architectures are required because of the specialized needs of systems and users. The combination of the arithmetic/logic unit and the control unit is called the central processing unit (CPU). 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 arithmetic/logic unit performs arithmetic and compares numerical values. 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.
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. Thus, computer architecture covers computer systems, microprocessors, circuits, and system programs.
Computer architecture refers to an entire structure and to the details needed to make it functional. The term also 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. Architecture (computer science) , a general term referring to the structure of all or part of a computer system.
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