CS 6461: Computer ArchitectureFall 2013

History and Trends

Instructor: Morris Lancaster

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Instructor

• Morris Lancaster– 703 400 6408

– Lancaster_morris@bah.com

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Computer Architecture

Instruction Set ArchitectureRefers to the instruction set that can be used by the

programmer or generated by a compiler

This logical view serves as the boundary between hardware and software

Can be compared with an interface specification or contract for an object – where given a set of preconditions, a given activity will always yield the same postconditions with respect to the architecture

View as the accessible register set and memory and the instructions that can be used to affect them

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Computer Architecture

OrganizationHigh level aspects of computer design, including memory

system, bus structure, design of the internal cpu, independent of the ISA.

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Computer Architecture

• Organization– Processors with two distinct organizations can support

the same ISA• NEC VR 5432 and VR 4122 both support MIPS 64 ISA

• VR 4122 does floating point in software and has different cache and pipeline than VR 5432

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Computer Architecture

• Hardware– The specifics of a machine’s detailed logic design and

packaging• Clock rates, voltages, etc.

Trends in Technology, Applications and Architectures

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Historical Perspective

• 1957 to early 1970s – Technology improvements:

• tubes to transistors to integrated circuits

– Organization improvements:• Larger register sets

• Increased number of buses

• Introduction of caches

• Introduction of pipelines

– Mainframes and minicomputers dominated the market

– “Big fish ate little fish”

– 25% to 30% per year performance growth contributed to by technology improvements and organization improvements

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Historical Perspective

• Late 1970’s through early 1980’s– Technology improvements:

• LSI to VLSI to not categorizing any more

• Facilitated 35% or more growth per year

– Organization improvements:• Few new improvements so as to have less impact than

technology

– Microprocessor based systems began to take over

– “little fish eat big fish?”

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Historical PerspectiveWhy microprocessor systems flourished

• Fundamental changes in software development and development environments– Assembly language development virtually eliminated, and

therefore applications became ISA (object code) independent (Intel’s/IBM’s lesson with 8080 and 8086)

– Standard OS (varieties of UNIX, Linux)

• Manufacturing costs were lower – The life cycle for design and development (and cost recovery) of

microprocessors was shorter, so improvements could be made quicker to produce higher performance processors

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Historical PerspectiveWhy microprocessor systems flourished

• Users could afford the new systems, especially those users with limited or no access to the corporate or university mainframe

• Given the fast turnaround for new designs and ISA independence, experimentation with new architectures was facilitated– Reduced Instruction Set Computer architectures

developed

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Historical PerspectiveAdvances in Computer Organization Begin Again

• RISC– Exploitation of instruction level parallelism

• Initially through pipelining and later through multiple instruction issue

– The use of caches• Initially simple and later more complex

– Intel IA 32 (x86) Architecture goes RISC• IA 32 instructions translated internally to RISC-Like instructions

• As transistor counts per chip soared this translation cost became negligible

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Historical PerspectiveAdvances in Computer Organization Begin Again

• Technology improvements continued and the combination of the technology and organization enhancements has led to 20 years of sustained growth in performance at an annual rate of over 50%. Organization enhancements have been the more significant portion of this growth.

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Historical PerspectivePerformance

?

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Historical PerspectiveChip Transistor Count

From Stallings, Computer Organization and Architecture – 8th Edition

Intel 1 Billion Transistor 2006

Intel 2 Billion Transistor 2008 (Article)

Sun Niagra 16 core andIBM Power 7 8 core (both 2 billion trans)

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Evolution

• Wide range of applications of computing– Desktop computing – business

• Now Workstations are on the Desktop

– High performance workstations

– Servers• Minicomputers replaced by microprocessors acting as

servers

– Supercomputers• Built from large numbers of microprocessors

– Embedded computers

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The Designer’s Challenges

• Rate of change of technology– Integrated circuit logic technology

• Transistor density increases at about 35% per year

• Increases in die size about 10% to 20% per year (better yields)

• Combined effect of about 55% per year increase in transistor count per chip

– DRAM• Density increases of 40% to 60% per year

– Magnetic Disk Technology• Greater than 100% per year

– Network Technologies• 10Mbps to 100Mbps to Gigabit

• Greater connectivity

Design Requirements/Constraints for Computer Architectures

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Requirements

• Who will program the machines• What do they expect?

– Performance?

– Low power consumption?

• How?– HLL, embedded, etc

• Compilation is key to performance– HW/SW interaction at ISA level

– Knowledge of architecture, application and algorithms

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The Designer’s Challengeswhat are the real requirements?

• Which of these has the best performance?

Airplane Passengers Range (mi) Speed (mph)Boeing 737- 100 101 630 598Boeing 747 470 4150 610BAC/Sud Concorde 132 4000 1350Douglas DC-8-50146 8720 544

How much faster is the Concorde compared to the 747? <2.213>

How much bigger is the 747 than the Douglas DC- 8? <3.5606>

bigger? faster? greatest range?What is the passenger mph ratio of the 747 compared to the

Concorde?<?>

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Industry Challenge

• Delays in delivery of a new technology can severely impact market position

• Life cycle for a particular product less than 5 years (e.g. Pentium II, Pentium III, Pentium IV)

• Cost• Inventory risk.• Other notes:

– In 2004 Intel cancelled all its high performance uniprocessor projects and joined IBM and Sun in declaring that the road to higher performance would be in multiple processors per chip.

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Focus of Text

• Look at the factors that made the last century’s incredible growth rate possible– Architectural ideas

– Accompanying compiler improvements

• Look at– Reasons for change

– Challenges and initial promising approaches

– Compilers

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Defining Computer Architectures

• Determine what attributes are important for a new computer

• Design the computer to maximize performance while staying within cost, power and availability constraints.– Instruction set design

– Functional organization

– Logic design

– Implementation• IC design

• Packaging

• Power

• Cooling

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Instruction Set Architecture

• 7 Dimensions– Class of ISA

• Register-memory 80x86

• Load-store MIPS

• Others– Stack

– Memory Addressing• Byte or word addressing

• Alignment

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Instruction Set Architecture

• 7 Dimensions (continued)– Addressing Modes

• Register, immediate, displacement – MIPS

• Add another displacement, register – older mainframe

– Operand Size• 8 bit

• 16 bit

• 32 bit

• 64 bit

• IEEE 32 bit single precision and 64 bit double precision, also 80 bit extended version

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Instruction Set Architecture

• 7 Dimensions (continued)– Operations

• Data Transfer• Arithmetic/Logical• Control• Floating Point

– Control flow• Conditional branches, unconditional jumps, procedure

calls, returns

– ISA encoding• Fixed length• Variable Length

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Instruction Set ArchitectureMIPS

• MIPS Instruction subset on Page 11

MIPS Formats Figure 1.6

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What Remains?

• Designing the organization and hardware to meet goals and functional requirements– Organization – high level aspects of a computer’s

design• CPU Design

• Memory Design and Interconnect

• ISA x86 AMD Opteron and Pentium 4 have very different internal designs

– Hardware – specifics, detailed logic design and packaging

• Pentium 4 versus Mobile Pentium 4

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Cost of an Integrated Circuit

• Cost of integrated circuit

• Cost of die

• Dies per wafer

Cost of die + cost of testing die + cost of packaging and final testdie yield

Cost of Wafer . Dies per wafer * die yield

π * (wafer diameter/2)2

die areaπ * wafer diameter

2*die area-

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Die Wafer

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Cost of an Integrated Circuit

• Die yield

Wafer yield * ( 1 + Defects per unit area * Die area α

)-α

.4 to .8 in 2001

A parameter that correspondsinversely to the number of masking levels

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Measuring and Reporting Performance

• Performance = 1 / Response time• Machine X is n times faster than machine Y

• = = n

• Example,– Machine X runs a program in 10 sec– Machine Y runs the same program in 15 sec

– 15 / 10 = 1.5 X is 1.5 times faster than Y

Performance X

Performance Y

Response time Y

Response time X

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Quantitative Performance

• Amdahl’s Law speedup =

Performance for entire task using enhancement when possiblePerformance for entire task without using the enhancement

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Quantitative Performance• A program is broken down into instructions

• Each instruction takes multiple clock cycles

• Instruction count (instructions executed, not static code)– Mostly determined by compiler and ISA

• CPI (average clock per instruction)– Mostly determined by ISA and CPU organization –CPI’s may differ according

to instruction –

• Clock rate– Mostly determined by technology and CPU organization

Time/program =# of instructions

a program

second

clock

# of clocks

# of instructions* *

= instruction count * CPI / clock rate

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Quantitative Principles

• Take advantage of parallelism• Understand Amdahl’s Law• Principle of Locality• Focus on the Common Case – make it fast