VonNeumann's principles, the control device, instruction sets and types of commands. Input-output and interruptions. Devices of storage of the computer. Memory hierarchy. The base memory and operation organization. Virtual storage. Input-output devices. The review of the modern hardware support.
Von Neumann's principles, the control device, instruction sets and types of commands
Von Neumann's Principles
• Principle of binary coding. For data representation and commands the binary numeral system is used.
• Principle of homogeneity of storage. Both programs (command) and the data are stored in the same storage (and they are encoded in the same numeration system – more often it is a binary system). It is possible to fulfill the same actions, as well as over the data.
• Principle of addressability of storage. Structurally the base memory consists of the enumerated cells; during the arbitrary moment of time any cell is accessible to the processor.
• Principle of serial program control. All commands are allocated in storage and fulfilled sequentially, one after another.
• A conditional branch Principle. Commands from the program aren't always fulfilled one after another. The presence at the program of conditional branch instructions which change sequence of performance of commands depending on data values is possible. (The principle was formulated before Von Neumann by Ada Lovelace and Charles Babbage’s; however it was logically included in Neumann's principle as an adding point to the previous principle.)
Principle of homogeneity of storage. Programs and data are stored in the same storage. Therefore the computer doesn't distinguish that it is stored in the given storage cell – number, the text or a command. Over commands it is possible to fulfill the same actions, as well as over the data.
It opens the variety of possibilities. For example, the program in the course of the performance also can be exposed to processing that allows setting in the program of a rule of obtaining of its some parts (so in the program performance of cycles and subroutines will be organized). Moreover, commands of one program can be received as results of execution of other program. Translation methods are based on this principle – text translation of the program from a high level programming language on language of the specific machine.
An addressing principle. Structurally the base memory consists of the renumbered cells; during the arbitrary moment of time any cell is accessible to the processor.
It gives an opportunity to give names to storage areas so that the values memorized in them can be changed afterwards in the course of performance of programs with the usage of appropriated names.
The computers constructed on these principles belong to the type of von Neumann. But there are computers different from von Neumann computers. The principle of program control, for example, cannot be fulfilled for them, i.e. they can work without «the instruction counter» specifying a current executed command of the program. To use any variable stored in the storage of these computers it is not mandatory to name it. Such computers are called as non von Neumann.