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Does not apply to John von Neumann's principles. Computer architecture

The foundations of the doctrine of computer architecture were laid by the outstanding American mathematician John von Neumann. He became involved in the creation of the world's first tube computer, ENIAC, in 1944, when its design had already been selected. During his work, during numerous discussions with his colleagues G. Goldstein and A. Berks, von Neumann expressed the idea of a fundamentally new computer. In 1946, scientists outlined their principles for constructing computers in the now classic article “Preliminary Consideration of the Logical Design of Electronic computing device". Half a century has passed since then, but the provisions put forward in it remain relevant today.

The article convincingly substantiates the use of the binary system to represent numbers (it is worth recalling that previously all computers stored processed numbers in decimal form). The authors convincingly demonstrated the advantages of the binary system for technical implementation, the convenience and simplicity of performing arithmetic and logical operations in it. Subsequently, computers began to process non-numeric types of information - text, graphic, sound and others, but binary coding of data is still information basis any modern computer.

Another truly revolutionary idea, the importance of which is difficult to overestimate, is the “stored program” principle proposed by Neumann. Initially, the program was set by installing jumpers on a special patch panel. This was a very labor-intensive task: for example, it took several days to change the program of the ENIAC machine (while the calculation itself could not last more than a few minutes - the lamps failed). Neumann was the first to realize that a program could also be stored as a series of zeros and ones, in the same memory as the numbers it processed. The absence of a fundamental difference between the program and the data made it possible for the computer to form a program for itself in accordance with the results of the calculations.

Von Neumann not only put forward the fundamental principles of the logical structure of a computer, but also proposed its structure, which was reproduced during the first two generations of computers. The main blocks according to Neumann are a control unit (CU) and an arithmetic-logical unit (ALU) (usually combined into a central processor), memory, external memory, input and output devices. It should be noted that external memory differs from input and output devices in that data is entered into it in a form convenient for a computer, but inaccessible to direct perception by a person. Thus, a magnetic disk drive belongs to external memory, and the keyboard is an input device, the display and print are output devices.

The control device and the arithmetic-logical unit in modern computers are combined into one unit - the processor, which is a converter of information coming from memory and external devices(this includes retrieving instructions from memory, encoding and decoding, performing various, including arithmetic, operations, coordinating the operation of computer components). The functions of the processor will be discussed in more detail below.

Memory (memory) stores information (data) and programs. Storage device modern computers“multi-tiered” and includes a random access memory (RAM) that stores the information with which the computer is working directly at a given time (an executable program, part of the data necessary for it, some control programs), and external storage devices (OSD) of much larger capacity, than RAM. but with significantly slower access (and significantly lower cost per 1 byte of stored information). The classification of memory devices does not end with RAM and VRAM - certain functions are performed by both SRAM (super-random access memory), ROM (read-only memory), and other subtypes of computer memory.

In a computer built according to the described scheme, instructions are sequentially read from memory and executed. Number (address) of the next memory cell. from which the next program command will be extracted is indicated by a special device - a command counter in the control unit. Its presence is also one of the characteristic features of the architecture in question.

The fundamentals of the architecture of computing devices developed by von Neumann turned out to be so fundamental that they received the name “von Neumann architecture” in the literature. The vast majority of computers today are von Neumann machines. The only exceptions are certain types of systems for parallel computing, in which there is no program counter, the classical concept of a variable is not implemented, and there are other significant fundamental differences from the classical model (examples include streaming and reduction computers).

Apparently, a significant deviation from the von Neumann architecture will occur as a result of the development of the idea of fifth-generation machines, in which information processing is based not on calculations, but on logical conclusions.

Von Neumann's principles

Principle of memory uniformity - Commands and data are stored in the same memory and are externally indistinguishable in memory. They can only be recognized by the method of use; that is, the same value in a memory cell can be used as data, as a command, and as an address, depending only on the way it is accessed. This allows you to perform the same operations on commands as on numbers, and, accordingly, opens up a number of possibilities. Thus, by cyclically changing the address part of the command, it is possible to access successive elements of the data array. This technique is called command modification and is not recommended from the standpoint of modern programming. More useful is another consequence of the principle of homogeneity, when instructions from one program can be obtained as a result of the execution of another program. This feature underlies translation - translation of program text from language high level into the language of a specific computer.

The principle of addressing - Structurally, the main memory consists of numbered cells, and any cell is available to the processor at any time. Binary codes of commands and data are divided into units of information called words and stored in memory cells, and to access them the numbers of the corresponding cells - addresses - are used.

Principle of program control - All calculations provided for by the algorithm for solving a problem must be presented in the form of a program consisting of a sequence of control words - commands. Each command prescribes some operation from a set of operations implemented by the computer. Program commands are stored in sequential memory cells of the computer and are executed in a natural sequence, that is, in the order of their position in the program. If necessary, using special commands, this sequence can be changed. The decision to change the order of execution of program commands is made either based on an analysis of the results of previous calculations, or unconditionally.

Binary coding principle - According to this principle, all information, both data and commands, is encoded with binary digits 0 and 1. Each type of information is represented by a binary sequence and has its own format. A sequence of bits in a format that has a specific meaning is called a field. In numeric information, there is usually a sign field and a significant digits field. In the command format, two fields can be distinguished: the operation code field and the addresses field.

3. Von Neumann's principles. Architecture of a classical computer, P von Neumann principles

The functioning of a computer is based on two fundamental concepts in computing. technology: concept of algorithm; principle of program control. An algorithm is a uniquely defined sequence of actions, consisting of formally defined operations on initial data, leading to a solution in a finite number of steps.

Properties algorithms

discreteness of information with which algorithms work; the finiteness and elementary nature of the set of operations performed when implementing the algorithm;

determinism - reproducibility of the results of the algorithm;

mass character - the possibility of using the algorithm for various initial data from an admissible set

A program is a description of an algorithm in any language.

Principle software management(PPU) was first formulated by the Hungarian mathematician and physicist John von Neumann, with the participation of Holtztein and Bertz in 1946 and is dominant at this stage in the development of computing technology.

PPU includes several architectural and functional principles.

1) Binary coding principle Information is encoded in binary form and divided into units (elements) of information called words. The use of the binary number system is determined by the specifics of electronic circuits. A word is an indivisible unit of information.

2) Uniformity of information coding. Different types of information words differ in the way they are used, but not in the way they are encoded. Words representing different types of information are indistinguishable (data, commands). The order in which they are used determines their specificity. The same commands can be used to process different data.

3) Address organization of RAM. Words of information are placed in machine memory cells and are identified by cell numbers called word addresses. Determines the specifics of storing and identifying information. The cell address is the machine identifier for the value and command.

4) The computer has a limited set of commands. Each individual command defines a simple (single) step of converting information.

5) The algorithm is implemented through sequential execution of commands. Performing calculations prescribed by the algorithm comes down to sequential execution of commands in an order uniquely determined by the program. The address of the next command is uniquely determined during the execution of the current command (conditional jumps are possible). The computation process continues until the command is executed to complete the computation. Advantages:

Ease of hardware implementation.

High versatility, which is limited only by the set of processor commands.

Flaws:

point 2: requires the programmer to correctly use data of various types; if they are not followed, errors appear that are often difficult to identify. When solving complex computing problems, this greatly increases the complexity of software development.

pz. assumes a linear organization of memory. This makes it difficult to calculate the layout elements of complex data types.

Classical architecturecomputer

Computer structure

In 1946, D. von Neumann, G. Goldstein and A. Berks, in their joint article, outlined new principles for the construction and operation of computers. Subsequently, the first two generations of computers were produced on the basis of these principles. There have been some changes in later generations, although Neumann's principles are still relevant today.

In fact, Neumann managed to summarize the scientific developments and discoveries of many other scientists and formulate something fundamentally new on their basis.

Von Neumann's principles

Use of the binary number system in computers. The advantage over the decimal number system is that devices can be made quite simple, and arithmetic and logical operations in the binary number system are also performed quite simply.

Computer software control. The operation of the computer is controlled by a program consisting of a set of commands. Commands are executed sequentially one after another. The creation of a machine with a stored program was the beginning of what we call programming today.

Computer memory is used not only to store data, but also programs.. In this case, both program commands and data are encoded in the binary number system, i.e. their recording method is the same. Therefore, in certain situations, you can perform the same actions on commands as on data.

Computer memory cells have addresses that are numbered sequentially. At any time, you can access any memory cell by its address. This principle opened up the possibility of using variables in programming.

Possibility of conditional jump during program execution. Despite the fact that commands are executed sequentially, programs can implement the ability to jump to any section of code.

The most important consequence of these principles is that now the program was no longer a permanent part of the machine (like, for example, a calculator). It became possible to easily change the program. But the equipment, of course, remains unchanged and very simple.

By comparison, the program of the ENIAC computer (which did not have a stored program) was determined by special jumpers on the panel. It could take more than one day to reprogram the machine (set jumpers differently). And although programs for modern computers can take years to write, they work on millions of computers after a few minutes of installation on the hard drive.

How does a von Neumann machine work?

A von Neumann machine consists of a storage device (memory) - a memory, an arithmetic-logical unit - ALU, a control device - CU, as well as input and output devices.

Programs and data are entered into memory from the input device through an arithmetic logic unit. All program commands are written to adjacent memory cells, and data for processing can be contained in arbitrary cells. For any program, the last command must be the shutdown command.

The command consists of an indication of what operation should be performed (from the possible operations on a given hardware) and the addresses of memory cells where the data on which the specified operation should be performed is stored, as well as the address of the cell where the result should be written (if it needs to be saved in memory).

The arithmetic logic unit performs the operations specified by the instructions on the specified data.

From the arithmetic logic unit, the results are output to memory or an output device. The fundamental difference between a memory and an output device is that in a memory, data is stored in a form convenient for processing by a computer, and it is sent to output devices (printer, monitor, etc.) in a way that is convenient for a person.

The control unit controls all parts of the computer. From the control device, other devices receive signals “what to do”, and from other devices the control unit receives information about their status.

The control device contains a special register (cell) called the “program counter”. After loading the program and data into memory, the address of the first instruction of the program is written to the program counter. The control unit reads from memory the contents of the memory cell, the address of which is in the program counter, and places it in a special device - the “Command Register”. The control unit determines the operation of the command, “marks” in memory the data whose addresses are specified in the command, and controls the execution of the command. The operation is performed by the ALU or computer hardware.

As a result of the execution of any command, the program counter changes by one and, therefore, points to the next command of the program. When it is necessary to execute a command that is not next in order to the current one, but is separated from the given one by a certain number of addresses, then a special jump command contains the address of the cell to which control must be transferred.

The vast majority of computers are based on the following: general principles, formulated in 1945 by the American scientist John von Neumann (Figure 8.5). These principles were first published in his proposals for the EDVAC machine. This computer was one of the first stored program machines, i.e. with a program stored in the machine's memory, rather than read from a punched card or other similar device.

Figure 9.5 - John von Neumann, 1945

1. Program control principle . It follows from it that the program consists of a set of commands that are executed by the processor automatically one after another in a certain sequence.

A program is retrieved from memory using a program counter. This processor register sequentially increases the address of the next instruction stored in it by the instruction length.

And since the program commands are located in memory one after another, a chain of commands is thereby organized from sequentially located memory cells.

If, after executing a command, it is necessary to move not to the next one, but to some other memory cell, conditional or unconditional jump commands are used, which enter the number of the memory cell containing the next command into the command counter. Fetching commands from memory stops after reaching and executing the “stop” command.

Thus, the processor executes the program automatically, without human intervention.

According to John von Neumann, a computer should consist of a central arithmetic-logical unit, a central control unit, a storage device, and an information input/output device. A computer, in his opinion, should work with binary numbers and be electronic (not electrical); perform operations sequentially.

All calculations prescribed by the algorithm for solving the problem must be presented in the form of a program consisting of a sequence of control words-commands. Each command contains instructions for the specific operation being performed, the location (addresses) of the operands and a number of service characteristics. Operands are variables whose values are involved in data transformation operations. A list (array) of all variables (input data, intermediate values and calculation results) is another integral element of any program.

To access programs, instructions and operands, their addresses are used. The addresses are the numbers of computer memory cells intended for storing objects. Information (command and data: numeric, text, graphic, etc.) is encoded with binary digits 0 and 1.

That's why Various types information stored in computer memory is practically indistinguishable; identification is possible only when the program is executed, according to its logic, in context.

2. The principle of memory homogeneity . Programs and data are stored in the same memory. Therefore, the computer does not distinguish between what is stored in a given memory cell - a number, text or command. You can perform the same actions on commands as on data. This opens up a whole range of possibilities. For example, a program can also be processed during its execution, which makes it possible to set rules for obtaining some of its parts in the program itself (this is how the execution of cycles and subroutines is organized in the program). Moreover, commands from one program can be obtained as results from the execution of another program. Translation methods are based on this principle - translating program text from a high-level programming language into the language of a specific machine.

3. Targeting principle . Structurally, main memory consists of renumbered cells; Any cell is available to the processor at any time. This implies the ability to name memory areas so that the values stored in them can later be accessed or changed during program execution using the assigned names.

Von Neumann's principles can be practically implemented in many different ways. Here we present two of them: a computer with a bus and a channel organization. Before describing the principles of computer operation, we introduce several definitions.

Computer architecture is called its description at some general level, including a description of user programming capabilities, command systems, addressing systems, memory organization, etc. The architecture determines the principles of operation, information connections and mutual connection of the main logical nodes of the computer: processor, RAM, external storage and peripheral devices. Commonality of architecture different computers ensures their compatibility from the user's point of view.

Computer structure is a set of its functional elements and connections between them. The elements can be the most various devices- from the main logical nodes of a computer to the simplest circuits. The structure of a computer is graphically represented in the form of block diagrams, with the help of which you can describe the computer at any level of detail.

The term is very often used computer configuration , which is understood as the layout of a computing device with a clear definition of the nature, quantity, relationships and main characteristics of its functional elements. The term " computer organization» determines how the computer’s capabilities are implemented,

Team – the collection of information necessary for the processor to perform a specific action when executing a program.

The team consists of operation code, containing an indication of the operation to be performed and several address fields, containing an indication of the location of the instruction operands.

The method of calculating an address from the information contained in the address field of a command is called addressing mode. The set of commands implemented in a given computer forms its command system.

In fact, Neumann managed to summarize the scientific developments and discoveries of many other scientists and formulate something fundamentally new on their basis.

Von Neumann's principles

Use of the binary number system in computers. The advantage over the decimal number system is that the devices can be made quite simple, arithmetic and logical operations in the binary number system they are also quite simple.
Software control computer. The operation of the computer is controlled by a program consisting of a set of commands. Commands are executed sequentially one after another. The creation of a machine with a stored program was the beginning of what we call programming today.
Computer memory is used not only to store data, but also programs.. In this case, both program commands and data are encoded in the binary number system, i.e. their recording method is the same. Therefore, in certain situations, you can perform the same actions on commands as on data.
Computer memory cells have addresses that are numbered sequentially. At any time, you can access any memory cell by its address. This principle opened up the possibility of using variables in programming.
Possibility of conditional jump during program execution. Despite the fact that commands are executed sequentially, programs can implement the ability to jump to any section of code.

How does a von Neumann machine work?

A von Neumann machine consists of a storage device (memory) - a memory, an arithmetic-logical unit - ALU, a control device - CU, as well as input and output devices.

The arithmetic logic unit performs the operations specified by the instructions on the specified data.

Von Neumann Principles (Von Neumann Architecture)

Computer architecture

In fact, Neumann managed to summarize the scientific developments and discoveries of many other scientists and formulate something fundamentally new on their basis.

Von Neumann's principles

Possibility of conditional jump during program execution. Despite the fact that commands are executed sequentially, programs can implement the ability to jump to any section of code.

How does a von Neumann machine work?

A von Neumann machine consists of a storage device (memory) - a memory, an arithmetic-logical unit - ALU, a control device - CU, as well as input and output devices.

The arithmetic logic unit performs the operations specified by the instructions on the specified data.

Von Neumann's principles[edit | edit source text]

The principle of memory homogeneity

Commands and data are stored in the same memory and are externally indistinguishable in memory. They can only be recognized by the method of use; that is, the same value in a memory cell can be used as data, as a command, and as an address, depending only on the way it is accessed. This allows you to perform the same operations on commands as on numbers, and, accordingly, opens up a number of possibilities. Thus, by cyclically changing the address part of the command, it is possible to access successive elements of the data array. This technique is called command modification and is not recommended from the standpoint of modern programming. More useful is another consequence of the principle of homogeneity, when instructions from one program can be obtained as a result of the execution of another program. This possibility underlies translation - the translation of program text from a high-level language into the language of a specific computer.

Targeting principle

Structurally, the main memory consists of numbered cells, and any cell is available to the processor at any time. Binary codes of commands and data are divided into units of information called words and stored in memory cells, and to access them the numbers of the corresponding cells - addresses are used.

Program control principle

All calculations provided for by the algorithm for solving the problem must be presented in the form of a program consisting of a sequence of control words - commands. Each command prescribes some operation from a set of operations implemented by the computer. Program commands are stored in sequential memory cells of the computer and are executed in a natural sequence, that is, in the order of their position in the program. If necessary, using special commands, this sequence can be changed. The decision to change the order of execution of program commands is made either based on an analysis of the results of previous calculations, or unconditionally.

Binary coding principle

According to this principle, all information, both data and commands, is encoded with binary digits 0 and 1. Each type of information is represented by a binary sequence and has its own format. A sequence of bits in a format that has a specific meaning is called a field. In numeric information, there is usually a sign field and a significant digits field. In the command format, two fields can be distinguished: the operation code field and the addresses field.

Von Neumann not only put forward the fundamental principles of the logical structure of a computer, but also proposed its structure, which was reproduced during the first two generations of computers. The main blocks according to Neumann are a control unit (CU) and an arithmetic-logical unit (ALU) (usually combined into a central processor), memory, external memory, input and output devices. The design diagram of such a computer is shown in Fig. 1. It should be noted that external memory differs from input and output devices in that data is entered into it in a form convenient for a computer, but inaccessible to direct perception by a person. Thus, the magnetic disk drive refers to external memory, and the keyboard is an input device, display and print are output devices.

Rice. 1. Computer architecture built on von Neumann principles. Solid lines with arrows indicate the direction of information flows, dotted lines indicate control signals from the processor to other computer nodes

The control device and the arithmetic-logical unit in modern computers are combined into one unit - the processor, which is a converter of information coming from memory and external devices (this includes retrieving instructions from memory, encoding and decoding, performing various, including arithmetic, operations, coordination of the operation of computer nodes). The functions of the processor will be discussed in more detail below.

Memory (memory) stores information (data) and programs. The storage device in modern computers is “multi-tiered” and includes random access memory (RAM), which stores the information with which the computer is working directly at a given time (the executable program, part of the data necessary for it, some control programs), and external storage devices (ESD). ) much larger capacity than RAM. but with significantly slower access (and significantly lower cost per 1 byte of stored information). The classification of memory devices does not end with RAM and VRAM - certain functions are performed by both SRAM (advanced random access memory), ROM (read-only memory), and other subtypes of computer memory.