G. Myers: Advances in Computer Architecture

Transcription

1 1 / 15 G. Myers: Advances in Computer Architecture P. A. Wilsey Univ of Cincinnati

2 2 / 15 Chapter 1: Introduction Computer architecture is largely a process of boundary determination. Given a definition of the function to be performed by the system as a whole, the computer architect s role is one of making trade-offs. Working with a set of criteria (which often conflict), such as cost, speed, and reliability, the architect determines which functions, or parts of functions belong inside the boundary and which belong outside the boundary.

3 3 / 15 Computer Architecture Design Process The process of computer architecture can be structured in a manner similar to most other design processes. Ideally, the architect approaches the task in the following order: 1. Requirements Analysis 2. Requirements Specification 3. Study of Prior Solutions 4. Conceptual Design 5. Detailed Design 6. Tuning 7. Evaluation

4 4 / 15 Requirements Analysis Requirements analysis: largely a study of the definition of the overall system architecture. Questions answered here may include: what are the characteristics of the programming languages to be provided, peripheral devices, and environment (real-time, commercial, scientific).

5 5 / 15 Requirements Specification Requirements specification: involving (1) a determination and weighing of design criteria, (2) the identification of the functions to be evaluated against these criteria, and (3) the identification of other factors (such as constraints imposed by the available manufacturing technology). Examples of criteria: Cost Reliability Feasibility Extensibility Compatibility Speed Security Risk Programming Ease

6 6 / 15 Study of Prior Solutions Study of Prior Solutions: what have others with similar constraints done and, more importantly, how successful was the resulting product.

7 7 / 15 Conceptual Design Conceptual Design: the core of the machine design process where trade off analysis occurs. Identification of placement of functions on either side of the hardware/software boundary.

8 8 / 15 Detailed Design Detailed Design: instruction types, formats, and semantics; data representation; addressing mechanisms; # of registers; and so on.

9 9 / 15 Study of Prior Tuning Tuning:

10 10 / 15 Evaluation Evaluation: In general, there will be many iterations through some or all of these 7 steps before a final design is realized.

11 11 / 15 Chapter 2: A Critique of the Conventional von Neumann Architecture Observation: Current computing systems have not been designed with a global study of the system function and its hardware/software trade offs. Instead, most computer architects have based their designs on tradition and the bottom-up view to minimize the cost of hardware and let the programmers solve all of the difficult problems. Substantiating Evidence: With very few exceptions, there have been no advances in computer architectures since the 1950s.

12 12 / 15 Semantic Gap Original Definition: A measure of the difference between the concepts in high-level languages and the concepts in the underlying computer architecture. Myers Extension: The gap between the concepts of the uses to which a computing system will be put and the concepts in the underlying architecture.

13 13 / 15 Consequence of the Semantic Gap 1. Software Unreliability: references to undefined (unassigned) variables out-of-bounds array references 2. Machine efficiency problems: a large number of instructions must be generated by the compiler and interpreted by the machine to realize each programming language construct. 3. Excessive program size: related to #2 above. This also has serious repercussions on compilation setting for error checking. Consider the PL/1 statement: C(I,J)=A(I,J)+B(J,I) 75 machine instructions (274 bytes) if bounds checking turned on 17 machine instructions (62 bytes) if bounds checking turned off 4. Compiler Complexity

14 14 / 15 Chapter 3: The Binding of Programs to Machines A: assembled C: compiled I: interpreted C Path 1 Low level machine language High level language program A C One for one machine language Intermediate machine language I Path 3 I Path 2 I Machine I Path 4

15 15 / 15 Chapter 4: Requisites for Improved Architectures 1. Self-Defining Data: Tags Descriptors Objects 2. Small Protection Domains: protection of a program or process from itself (i.e., protecting a subroutine and its data from other subroutines). protection of a program from system software. 3. Subroutine Management 4. Capability-Based Addressing 5. Single-Level Store 6. Process Management