UMBC A B M A L T F O U M B C I M Y O R T 1 (June - PowerPoint PPT Presentation

Advanced Computer Architecture Chapter 1 (Part I) CMSC 611 Course Summary Improvements in CPU performance a result of: • Technology enhancements (already discussed). • Improvements in computer architecture: Innovations • Improvements in accompanying compilers. Focus of this course is on how the second two have contributed to recent per- formance improvements. L A N R Y D UMBC A B M A L T F O U M B C I M Y O R T 1 (June 14, 2000 4:18 pm) I E S R C E O V U I N N U T Y 1 6 9 6

Advanced Computer Architecture Chapter 1 (Part I) CMSC 611 Designer Tasks: Determine the important attributes of a new machine. Maximize performance while staying within cost constraints. Non-trivial. Task aspects: Instruction set architecture (used to be the only focus). Functional organization: High level aspects of computer design, i.e. memory system, bus architecture and internal CPU design. Logic design (hardware) Implementation (hardware) L A N R Y D UMBC A B M A L T F O U M B C I M Y O R T 2 (June 14, 2000 4:18 pm) I E S R C E O V U I N N U T Y 1 6 9 6

Advanced Computer Architecture Chapter 1 (Part I) CMSC 611 Designer Tasks: Architect MUST consider: Functional requirements , cost and performance goals. Former goal is difficult to determine. Requires determination of application software to be used (what pro- grams will be run ?), which may influence instruction set design. Design complexity: Complex designs take longer to complete (increases time-to-market). Complex designs must provide higher performance to be competitive. Technology trends: Not only what’s available today, but also what will be available when the system is ready to ship. (more on this later) L A N R Y D UMBC A B M A L T F O U M B C I M Y O R T 3 (June 14, 2000 4:18 pm) I E S R C E O V U I N N U T Y 1 6 9 6

Advanced Computer Architecture Chapter 1 (Part I) CMSC 611 Trends: Computer usage trends: The amount of memory used by programs increases by a factor of 1.5 to 2 per year (1/2 to 1 address bits consumed/year) ! Underestimating this is often the major reason an instruction set archi- tecture must be abandoned. An increase in compiler dependency: Compilers have become the primary interface between the user and machine (migration from assembly to high level languages). Compilers are relied upon to transform code to improve pipeline behav- ior and memory system behavior. How does compiler usage influence your design ? L A N R Y D UMBC A B M A L T F O U M B C I M Y O R T 4 (June 14, 2000 4:18 pm) I E S R C E O V U I N N U T Y 1 6 9 6

Advanced Computer Architecture Chapter 1 (Part I) CMSC 611 Trends: Implementation technology: IC Technology: Feature size reduced by 30% every 3 years, doubling density every 3 years (33% more transistors/unit area/year w.r.t 1st year). Die size increases necessary to achieve 59% more transistors/chip/year, in accordance with Moore’s law: Number of functions doubled every 1.5-2 years. Challenge: Cost/function reduction of 25-30%/year. DRAM (memory): Cycle time improvements are slow , decreasing by ~1/3 in 10 years. Remember, bandwidth is proportional to cycle time and the width of the data path. L A N R Y D UMBC A B M A L T F O U M B C I M Y O R T 5 (June 14, 2000 4:18 pm) I E S R C E O V U I N N U T Y 1 6 9 6

Advanced Computer Architecture Chapter 1 (Part I) CMSC 611 Trends: Implementation technology: Disk technology: Density improves by 25%/yr (~2x in 3 years). Bandwidth increases by 25%/yr, which is proportional to the square root of density (and to rotation speed, which increases very slowly). Access (seek) time increases slowly , 1/3 in 10 years. Conclusion: The designer must take these improvements into account and design for a future technology. By the time the system ships, the future will be the present and the design MUST be optimal for this technology in order to be competitive. L A N R Y D UMBC A B M A L T F O U M B C I M Y O R T 6 (June 14, 2000 4:18 pm) I E S R C E O V U I N N U T Y 1 6 9 6

Advanced Computer Architecture Chapter 1 (Part I) CMSC 611 Trends: Cost trends: Understanding trends in component costs (how they will change over time) is an important issue for designers. Remember, you design for tomorrow and what’s NOT affordable today may be affordable tomorrow. Observation 1: Component prices drop over time without major improvements in man- ufacturing technology. Why ? The learning curve . Consider yield (the number of good devices/total number of devices). In general, a chip, board or system with twice the yield will have half the cost. Problem: The learning curve is different for different components. This complicates new system design decisions. L A N R Y D UMBC A B M A L T F O U M B C I M Y O R T 7 (June 14, 2000 4:18 pm) I E S R C E O V U I N N U T Y 1 6 9 6

Advanced Computer Architecture Chapter 1 (Part I) CMSC 611 Trends: Cost trends: Observation 2 : Volume. Larger volume increases rate of the learning curve. (Products get cheaper to manufacture more quickly). Volume decreases cost due to increases in manufacturing efficiency. Development cost amortization allows cost to get closer to selling price. Therefore, The more you make, the less it costs ! L A N R Y D UMBC A B M A L T F O U M B C I M Y O R T 8 (June 14, 2000 4:18 pm) I E S R C E O V U I N N U T Y 1 6 9 6

Advanced Computer Architecture Chapter 1 (Part I) CMSC 611 Cost: IC cost analysis: Cost of die + Cost of testing + Cost of packaging and final test Cost of IC = - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Final test yield Cost of wafer Cost of die = - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - × Dies/wafer Die yield The bigger the die, the higher its cost since “Dies/wafer” gets smaller. What about “Die yield” ? L A N R Y D UMBC A B M A L T F O U M B C I M Y O R T 9 (June 14, 2000 4:18 pm) I E S R C E O V U I N N U T Y 1 6 9 6

Advanced Computer Architecture Chapter 1 (Part I) CMSC 611 Cost: IC cost analysis: What about yield (the number of good dies/wafer) ? A simple model:  α – ×  Defects per unit area Die size × Die yield = Wafer yield 1 + - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -   α “ W afer yield” accounts for wafers that ar e completely bad. This model assumes defects are randomly distributed. In 1995, it was between 0.6 to 1.2 per cm 2 . (Learning curve allows us to reduce this value over time). ‘alpha’ corresponds to the number of masking levels (complexity). It is approximately 3.0 today. What is the yield assuming 100% wafer yield, 0.8/cm 2 defect density and a die size of 1.5 cm ? L A N R Y D UMBC A B M A L T F O U M B C I M Y O R T 10 (June 14, 2000 4:18 pm) I E S R C E O V U I N N U T Y 1 6 9 6

Advanced Computer Architecture Chapter 1 (Part I) CMSC 611 Cost: IC cost analysis: Bottom line: The number of good dies/wafer = dies/wafer * die yield. The larger and/or more complex the chip, the more costly - its NOT a linear relationship. The designer controls only the die size: Decides which features/functions are included and which are excluded. A decision not to be taken lightly because: f Die area4 ( ) for α Cost of die = = 3.0 A strong incentive to reduce feature size, instead of increasing die size. L A N R Y D UMBC A B M A L T F O U M B C I M Y O R T 11 (June 14, 2000 4:18 pm) I E S R C E O V U I N N U T Y 1 6 9 6

Advanced Computer Architecture Chapter 1 (Part I) CMSC 611 Cost vs. Price: Definitions: Component costs: Raw material cost. Direct cost: Costs incurred to make a single item. Adds 20% to 40% to component cost. Gross margin ( Indirect cost): Overhead not associated with a single item, i.e. R&D, marketing, manufacturing equipment, taxes, etc. Average Selling Price (ASP): Component cost + direct cost + indirect cost. List price : Not ASP. Stores add to the ASP to get their cut. Want 50% to 75% of list price. L A N R Y D UMBC A B M A L T F O U M B C I M Y O R T 12 (June 14, 2000 4:18 pm) I E S R C E O V U I N N U T Y 1 6 9 6