THE CONCEPT OF COMPUTER ARCHITECTURE Chapter No. 2

Evolution of the Concept of Computer Architecture zThe term computer architecture evolved in1964 by the chief architects of IBM System/360. zThey interpreted computer architecture as the structure of machine that the assembly language programmer must understand to write a correct program for a machine. zBell and Newell in 1970 gave the concept of computer architecture by introducing a hierarchical, multilevel description. They identified four levels as the electronic circuit level, the logic design level, the programming level, and the processor-memory-switch (PMS) level.

Evolution of the Concept of Computer Architecture zSima in 1977 and Dasgupta in 1981 extend the concept by introducing the two dimensional concept of computer architecture which is equally distributed to functional specification and and the hardware implementation.

Recent Interpretation of the Concept of Computer Architecture zNow the interpretation of computer architecture covers the three aspects: yunderlying computational model xVon Neumann, dataflow, … yLevel of consideration xmicromachine, processor, computer system yScope of interest xfunctional specification, implementation

Recent Interpretation of the Concept of Computer Architecture Underlying computational model Level of consideration Scope of interest

Underlying Computational Model

Level of Abstraction

Scope of Interest Scope of interest Functional specification Implementation Computer Black box view Abstract architecture(logical architecture, external architecture, exo architecture, behavioral description, programming model ) Concrete architecture (physical architecture, internal architecture, endo-architecture, structural architecture) Internal structure and operation

Interpretation of the Concept of Computer Architecture at Different Levels of Abstraction zThe term computer architecture can be used at any level depending upon the scope interest. zIf scope of interest is functional then architecture is termed as abstract. zIf scope of interest is implementation then architecture is termed as concrete.

Abstract Architecture zAlso known as exo-architecture,external or logical architecture, a black box description, or in certain context as a programming model or a behavioral description. zThe abstract architecture is the black box specification and considers two different point of views: yprogrammers point of view xdealing with the programming model yhardware designer’s point of view xdealing with the hardware model. It also incorporates additional specifications like interface protocols

Concrete Architecture zAlso known as endo-architecture, internal or physical architecture or structural description. zHow a computer is implemented at a particular level of abstraction. zE.g. at the system level the description of the concrete architecture is based on processor level building blocks, such as processors, memories,buses and so on. zThe concrete architecture also considers two different point of views: ylogic design yphysical design

Concrete Architecture zPhysical design ybased on concrete circuit elements used, the specifications of signals, the interconnection of circuit elements, the declaration of initiated signal sequences. zLogic design ylogic design is an abstraction of physical design. yThe declaration of logical components used such as registers, execution units etc, their interconnections and the specification of the sequence of information transfers, which are initiated by each declared function.

Concrete Architecture of Computer System

Abstract Architecture of Processors (Architecture) zThe abstract architecture of a processor is often referred to as simply the architecture of the processor

Abstract Architecture of Processors (Architecture) zThe hardware model of the processor is a description from the hardware designer’s point of view. Here, the processor is considered as a building block of a computer system. This can be specified by three interfaces: the programming interface, the interrupt interface and the I/O interface I/O interface

Concrete Architectures of Processors (Micro Architecture) zThe concrete architecture of a processor is often referred to as the microarchitecture.

Abstract Architecture of an Operating System zThe abstract architecture of an operating system means the functional specifications.

Abstract Architecture of an Operating System Application programs Operating system Data Carrier Data carrier interface Logical I/O interface I/O controller User interface Application program interface

Concrete Architecture of an Operating System zIn order to interpret the concrete architecture of an operating system, its building blocks, their interconnections and its operation have to be specified. zIn this case, the building blocks are the main components of the operating system, such as memory management, processor management, I/O management, and so on.

Description Of Computer Architectures Description of architectures Informal description Formal description