Architecture and organization

Read the following words and word combinations and use them for understanding and translation of the text:

to adapt to - приспособиться к

instruction set - набор команд

to span - измерять, (перен.) охватывать

to encompass - заключать в себе, охватывать

enhancement - расширение

without regard to - независимо от, безотносительно к

in a sequential fashion - последовательно

explicitly - ясно, подробно

intrinsically - в действительности, по сути

to emerge - появляться

to evince - показывать, доказывать

compatibility - совместимость

interplay (between) - взаимодействие

Computer science often distinguishes between abstraction and implementation - i.e. between the general and the particular. We may examine any computer system at two major levels: its architecture and its organization.

The architecture of a computer system is the abstraction equivalent to the user-visible interface: the structure and the operation of the system as viewed by the assembly language programmer and the compiler-writer. If an architecture is well-designed, well-engineered to adapt to future technologies, it may persist for a decade or longer.

The organization of a computer is the realization and construction of that interface and structure out of specific hardware (and possibly software) components. Because of technological advances, any particular implementation (i.e., one model) may only be actively marketed for a relatively short period of time.

Examples of architectural attributes include the instruction set, the number of bits used to represent various data types (e.g., numbers, characters), I/O mechanisms, and techniques for addressing memory. Organizational attributes include those hardware details transparent to the programmer, such as control signals; interfaces between the computer and peripherals; and the memory technology used.

For example, it is an architectural design issue whether a computer will have a multiply instruction. It is an organizational issue whether that instruction will be implemented by a special multiply unit or by a mechanism that makes repeated use of the add unit of the system.

Historically, and still today, the distinction between architecture and organization has been an important one. Many computer manufacturers offer a family of computer models, all with the same architecture but with differences in organization. Consequently, the different models in the family have different price and performance characteristics. Furthermore, a particular architecture may span many years and encompass a number of different computer models, its organization changing with changing technology. A prominent example of both these phenomena is the IBM System 370 architecture. This architecture was first introduced in 1970 and included a number of models. Over the years, IBM has introduced many new models with improved technology to replace older models, offering the customer greater speed, lower cost, or both. These newer models retained the same architecture so that the customer’s software investment was protected. Remarkably, the System 370 architecture, with a few enhancements, has survived to this day IBM’s mainframe product line.

The modern computer is a remarkably complex and sophisticated device, but its fundamental principles of operation have really changed remarkably little since the earliest mechanical computers, and in particular, since IAS machine designed by John von Neumann at the Institute for Advanced Studies, Princeton, in the 1940s. The so-called von Neumann architecture is at the heart of almost every modern information processing system. It is based on three key concepts:

- data and instructions are stored in a single read-write memory,

- the contents of this memory are addressable by location, without regard to the type of data contained there,

- execution occurs in a sequential fashion (unless explicitly modified) from one instruction to the next.

Contemporary architectures fall into three classes. Complex Instruction Set Computers (CISC) typically include large numbers of machine instructions of many different styles. That complexity poses difficulties of implementation, because each style of instruction may require substantial real estate on the computer chip. Reduced Instruction Set Computers (RISC) are defined by smaller numbers of machine instructions of very few styles. The savings in space on a computer chip can, in favorable situations, make possible intrinsically faster circuitry. RISC programs can thus potentially execute faster than CISC programs, even though they usually contain more machine instructions. The third and newest class of contemporary architecture, Explicitly Parallel Instruction Computers (EPIC), includes the Itanium architecture.

Computer architectures may also be classified according to the width of the datapath, the internal components through which information flows, e.g., 64 bits for Itanium architecture.

When new architectures emerge, they may appear to be evolutionary because they evince strong family resemblances to earlier architectures from the same vendor. On the other hand, they appear revolutionary because they offer a clean break with the past.

In a class of computers called microcomputers, the relationship between architecture and organization is very close. Changes in technology not only influence organization but also result in the introduction of more powerful and more complex architectures. Generally, there is less of a requirement for generation-to-generation compatibility for these smaller machines. Thus, there is more interplay between organizational and architectural design decisions.

Notes:

IAS - Institute for Advanced Studies, Princeton

CISC (Complex Instruction Set Computer) - процессор со сложным набором команд - традиционная архитектура процессоров

RISC (Reduced Instruction Set Computer) - компьютер с сокращенным набором команд

EPIC (Explicitly Parallel Instruction Computer) – компьютер с заданным параллелизмом команд. В этой технологии компилятор говорит процессору, какие команды можно исполнять параллельно, а какие зависят от других команд