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 1 (June 14, 2000 4:18 pm)

UMBC

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.

Advanced Computer Architecture Chapter 1 (Part I) CMSC 611 2 (June 14, 2000 4:18 pm)

UMBC

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)

Advanced Computer Architecture Chapter 1 (Part I) CMSC 611 3 (June 14, 2000 4:18 pm)

UMBC

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)

Advanced Computer Architecture Chapter 1 (Part I) CMSC 611 4 (June 14, 2000 4:18 pm)

UMBC

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 ?

Advanced Computer Architecture Chapter 1 (Part I) CMSC 611 5 (June 14, 2000 4:18 pm)

UMBC

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.

Advanced Computer Architecture Chapter 1 (Part I) CMSC 611 6 (June 14, 2000 4:18 pm)

UMBC

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

• f 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.

Advanced Computer Architecture Chapter 1 (Part I) CMSC 611 7 (June 14, 2000 4:18 pm)

UMBC

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.

Advanced Computer Architecture Chapter 1 (Part I) CMSC 611 8 (June 14, 2000 4:18 pm)

UMBC

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 !

Advanced Computer Architecture Chapter 1 (Part I) CMSC 611 9 (June 14, 2000 4:18 pm)

UMBC

Cost: IC cost analysis: The bigger the die, the higher its cost since “Dies/wafer” gets smaller. What about “Die yield” ? Cost of IC Cost of die Cost of testing Cost of packaging and final test + + Final test yield

• =

Cost of die Cost of wafer Dies/wafer Die yield ×

• =

Advanced Computer Architecture Chapter 1 (Part I) CMSC 611 10 (June 14, 2000 4:18 pm)

UMBC

Cost: IC cost analysis: What about yield (the number of good dies/wafer) ? A simple model: “ 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 cm2. (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/cm2 defect density and a die size of 1.5 cm ? Die yield Wafer yield 1 Defects per unit area Die size × α

• +

    α – × =

Advanced Computer Architecture Chapter 1 (Part I) CMSC 611 11 (June 14, 2000 4:18 pm)

UMBC

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: A strong incentive to reduce feature size, instead of increasing die size. Cost of die f Die area4 ( ) = for α 3.0 =

Advanced Computer Architecture Chapter 1 (Part I) CMSC 611 12 (June 14, 2000 4:18 pm)

UMBC

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.

Advanced Computer Architecture Chapter 1 (Part I) CMSC 611 13 (June 14, 2000 4:18 pm)

UMBC

Cost vs. Price: Cost goes through a number of changes before it becomes price. This gives you insight on how a design decision will affect selling price, i.e. changing cost by $1,000 increases selling price by $3,000 to $4,000. Also, consider volume and price relationship: In general, the fewer computers that are sold, the higher the price. Also, a decrease in volume causes cost to increase, further increasing price. Therefore, small changes in cost can have an unexpected large increase in price.