IntroductionIntroduction

Computer ArchitectureComputer Architecture

Modern Computers

• Advancing at a rapid pace– Integral part of daily life

• Almost every aspect of human civilization now depends on it!

– Started to perform mathematical calculations• Reduce human errors• Increased speed

– Evolved into a complex, versatile machine• Store, retrieve, & process voluminous data

– At very high speeds

• Intuitive human-machine interface– Used for communication & entertainment as well

Managing Complexity• Increased complexity poses many challenges

– Exacerbates design, manufacturing, usage, and maintenance

• Solution: Multi-facetted Abstraction– Abstraction of data

• Store & process digital rather than analog data– Better control on the electronics/physics of the machine

– Abstraction of layers• Multi-tiered design • Each tier provides a more simplified view of underlying physics

– Abstraction of components• System built as a collection of sub-systems with well defined

behavior and functionality• Special interconnections between sub-systems

– Abstraction of control• In the form of software

Transistors

IC Chips

Cards & Devices

PC

A peek under the hood of a PC

• Major components of a PC– Main board aka Motherboard

• They are all Printed Circuit Board (PCB)– PCB is a multi-layered, rigid plastic sheet with copper wires etched

directly on it and permit ICs and electronic components to be mounted and soldered.

– Microprocessor/CPU• The brain and heart of the computer. It processes instructions to

manipulate data

– RAM or Main memory• RAM: Random Access Memory• High speed read/write memory for storing instructions and data

– Buses: Collection of wires that interconnect components• FSB: Front-Side-Bus interconnects CPU to main memory

Anatomy of a PC

CPU

North Bridge

RAM Video Card

South Bridge AudioHard Disk Drive (HDD)

ConnectivityUSB

Keyboard & MouseSuper I/O

Network PCI Slots

Parallel & Serial Ports

Floppy

Common Units

• It is important to know and understand the common units used for– Time (base unit: second)

• Derived units:– Millisecond (msec): 10-3 seconds– Microsecond (usec): 10-6 seconds– Nanosecond (nsec): 10-9 seconds– Picoseconds (psec): 10-12 seconds

– Frequency (base unit: Hertz or Hz)• Note that time and frequency are inversely related• Derived units:

– Kilohertz (KHz): 103 Hz– Megahertz (MHz): 106 Hz– Gigahertz (GHz): 109 Hz

Common Units (Contd.)• It is important to know and understand the common

units used for– Memory size (base unit: byte)

• Derived units:– Kilobyte (KB): 103 bytes– Megabyte (MB): 106 bytes– Gigabyte (GB): 109 bytes– Terabyte (GB): 1012 bytes– Petabyte (GB): 1015 bytes

• Do not confuse above units with KiB/MiB/GiB– Units with a “i” in the middle are powers of 1024 rather than 1000.– For example 1 MiB = 10242 bytes.

– FLOPS (base unit: FLOPS)• Derived units:

– Megaflop (MFLOP): 106 FLOPS– Gigaflop (MFLOP): 109 FLOPS– Teraflop (MFLOP): 1012 FLOPS– Petaflop (MFLOP): 1015 FLOPS

RAM

• Random Access Memory (RAM)– Volatile memory used to store data

• Data is lost when power is lost

– Most frequently accessed by the CPU– A PC will not boot unless there is some RAM on the main

board

• Therefore it must operate fast.• Typically 20-70 nanoseconds (10-9 seconds)

– Is available in a variety of sizes, technologies, and speeds

• Latest and greatest is DDR3

North & South Bridge

• The North & South Bridges are special Integrated circuits (ICs) (aka chips) that interconnect various components on a computer– These are often called chipsets

• Some computers (namely those from AMD) have the functionality of the Northbridge already fabricated on the CPU itself and don’t need a special chip for it.

– They are specific to the microprocessor and type of devices present on a computer

CPU

• The Central Processing Unit (CPU) aka Microprocessor (p)– The brain of the computer– Its task is to execute instructions

• It keeps on executing instructions from the moment it is powered-on to the moment it is powered-off.

• Execution of various instructions causes the computer to perform various tasks.

– There are a wide range of CPUs • We will study CPUs in detail in this course• The dominant CPUs on the market today are from

– Intel: Pentium (Desktop), Xeon (Server), Pentium-M (Mobile), X-scale (Embedded)

– AMD: Athlon (Desktop), Opteron (Server), Turion (Mobile), Geode (Embedded)

Key Characteristics of a CPU• Several metrics are used to describe the characteristics of a CPU

– Native “Word” size• 32-bit or 64-bit

– Clock speeds• The clock speed of a CPU defines the rate at which the internal clock of the

CPU operates– The clock sequences and determines the speed at which instructions are executed by

the CPU• Modern CPUs operate in Gigahertz (1 GHz = 109 Hz)• However, clock speeds alone do not determine the overall ability of a CPU

– Instruction set• More versatile CPUs support a richer and more efficient instruction sets• Modern CPUs have new instruction sets such as SSE, SSE2, 3DNow that

can be used to boost performance of many common applications– These instructions perform the operation of several instructions but take less time

– FLOPS: Floating Point Operations per Second• FLOPS are a better metric for measuring a CPU’s computational capabilities• Modern CPUs deliver 2-3 Giga FLOPS (1 GFLOPS = 109 FLOPS)• FLOPS is also used as a metric for describing computational capabilities of

computer systems– Modern supercomputers deliver 1 Terra Flop (TFLOP), 1 TFLOP = 1012 FLOPS.

Key Characteristics of a CPU (Contd.)• Several metrics are used to describe the characteristics of a CPU

– Power consumption• Power is an important factor in today’s computing• Power is the product of voltage applied to the CPU (V) and the amount of

current drawn by the CPU (I)» The unit for voltage is volts» The unit for current is ampere (aka amps)

– Power = V x I – Power is typically represented in Watts– Modern desktop processors consume anywhere from 35 to 100 watts

• Lower power is better as power is proportional to heat– More power implies the processor generates more heat and heating is a big problem

– Number of computational units of core per CPU• Some CPUs have multiple cores • Each core is an independent computational unit and can execute instructions

in parallel• More the number of cores the better the CPU is for multi-threaded

applications– Single threaded applications typically experience a slow down on multi-core processors

due to reduced clock speeds

Key Characteristics of a CPU (Contd.)• Several metrics are used to describe the characteristics of a CPU

– Cache size and configuration• Cache is a small, but high speed memory that is fabricated along with the

CPU– Size of cache is inversely proportional to its speed– Cost of the CPU increases as size of cache increases

• It is much faster than RAM• It is used to minimize the overall latency of accessing RAM• Microprocessors have a hierarchy of caches

– L1 cache: Fastest and closest to the core components– L3 cache: Relatively slower and further away from CPU

– Example cache configurations (See comparative die images):• Quad core AMD Opteron (Shanghai)• 32 KB (Data) + 32 KB (Instr.) L1 cache per core• Unified 512 KB L2 cache per core• Unified 6 MB shared L3 cache (for 4 cores)

– Quad core Intel Xeon (Nehalem)• 32 KB (Data) + 32 KB (Instr.) L1 Cache per core• Unified 256 KB L2 cache per core• Unified 8 MB shared L3 cache (for 4 cores)

Trends in computing

• Until recently, hardware performance improvements have been primarily achieved due to advancement in microprocessor fabrication technologies:– Steady improvement in processor clock speeds

• Faster clocks (with in the same family of processors) provide higher FLOPS

– Increase in number of transistors on-chip• More complex and sophisticated hardware to improve

performance• Larger caches to provide rapid access to instruction

and data

Moore’s Law• The steady advancement in microprocessor technology

was predicted by Gordon Moore (in 1965), co-founder of Intel– Moore’s law states that the number of transistors on

microprocessors will double approximately every two years.• Many advancements in digital technologies can be linked to Moore’s

law. This includes:– Processing speed– Memory Capacity– Speed and bandwidth of data communication networks and – Resolution of monitors and digital cameras

– Thus far, Moore’s law has steadily held true for about 40 years (from 1965 to about 2005)

– Breakthroughs in miniaturization of transistors has been the turnkey technology

• See comparative technical video (Courtesy Intel)• See trends from a non-technical perspective (Courtesy Intel)

Moore’s Law vs. Intel’s roadmap• Here is a graph illustrating the progress of Moore’s law based on Intel

Inc. technological roadmap (obtained from Wikipedia)

Stagnation of Moore’s Law• In the past few years we have reached the

fundamental limits at IC fabrication technology (particularly lithography and interconnect)– It is no longer feasible to further miniaturize the

transistors on the IC• They are already just a several atoms large and at this point

laws of physics change making it an extremely challenging task

– Heat dissipation has reached breakdown threshold• Heat is generated as a part of regular transistor operations• Higher heat dissipations will cause the transistors to fail

• With the current state of the art a single processor cannot yield any more than 4 to 5 GFLOPS– How do we move beyond this barrier?

Multi-core and Multi-processors

• The solution to increasing the effective compute power is via the use of multi-core, multi-processor computer system along with suitable software– This is a paradigm shift in hardware and software

technologies– Multiple cores and multiple processors are

interconnected using a variety of high speed data communication networks

– Software plays a central role in harnessing the power of multi-core/multi-processor systems

• Most industry leaders believe this is the near future of computing!

Multi-core Trends• Multi-core processors are most definitely the future of computing

– Both Intel and AMD are pushing for larger number of cores per CPU package

– The Cell Broadband Engine (aka Cell) has 8 synergistic processing elements (SPE)

– The Sun Microsystems Niagara has 8 cores, with each core capable of running 8-threads

• Here is a short video from Intel demonstrating their proof-of-concept, next generation Tera-chip designed to deliver a teraflop of compute power from a single CPU package.

Manufacturing ICs

• Manufacturing of Integrated Circuits (ICs) in a complex process– Almost all the phases are completely automated

• Use Computer Aided Manufacturing (CAM)• Manufacturing plants where the ICs are fabricated are

called “Fabs”

– Everything is computerized and software driven• Extensive Computer Aided Design (CAD)• Testing of designs is performed using simulations

CPU Manufacturing Process

Computer Aided Design (CAD)

Simulation-based Testing

Mask Design for Photolithography

Silicon Manufacturing

Silicon Wafer

Multiple phases of Photolithography

Wafer with multiple CPUs

Testing & Dicer

Packaging

Tested Dies

Testing & Shipping to OEMs & Retail

Computer Architecture

• Science to enable effective engineering of digital computers. – This is a complex field that spans various levels

of hierarchy• Component level• Device level• Device interconnection• CPU design

– This is where most of the R&D work lies

• Development of firmware and BIOS

Why do we need Comp. Arch.?

• Effective use of modern computers– Optimal software development

• Crucial for embedded computing• Important for system programming

– Development of operating systems

– Design of device drivers and custom software

• Tap into high performance features• Avoid hidden bottlenecks

– Know hidden pitfalls

– Prudent economic investment• Know what you need & buy what you need

– Don’t waste your money

• Know what you are buying

– Design & development of hardware

Goals of this class

• To understand:– Design of a PC– Working and functionality of various components

and subsystems in a PC– Develop initial set of skills to program a computer

at a low level via assembly• It is an important part in developing a hardware-

software interface using a hierarchy of language translators

Hardware-Software Interface

• The interface between hardware and software is achieved using a hierarchy of translators – Hierarchy helps to

balance:• Portability &

Interoperability• Development overhead

vs. performance• Design & manufacturing

Typical Hierarchy:

Program/software in a High-level Language (C/C++)

Compiler

Translated code in Assembly

Assembler

Machine Language

if (a > b) { c = a;} else { c= b;}

cmp a,bjg elsePartmov a,cjmp endifelsePart: mov b,cendif:

000101111010101000100101010101000111010101011010101010101010101

Semantic Gap• Semantic gap is a term that is used to describe

– The disconnect between a high level programming language (such as: Java, C++, or C) and the underlying hardware architecture

– It is used to refer to the distinction between the conceptual view (from a programmer’s perspective) versus the actual operations of a CPU

• Small semantic gap is desirable– High level programming languages have large semantic gaps

• Prevent effective use of underlying hardware– Assembly has small semantic gap

• Higher performance comes at the price of higher software development overheads

• Hierarchy of translators essentially attempt to bridge the semantic gap– Bridging the gap often requires significant human intervention

Plan of Action

• Study in a bottom-up fashion– Digital logic / Boolean algebra

• Logic gates• Logic circuits (Interconnection of gates)

– Number representation using digital logic• Memory circuits• Arithmetic circuits

– Arithmetic & Logic circuits – Processor (or CPU)• Programming the CPU in Assembly language

– We will spend good deal of time here

• Learn about performance enhancement strategies– Most computer architecture work lies in this area