Chapter 5Computing Components

The (META) BIG IDEACool, idea but maybe too big

• DATA– Must be stored somewhere in a storage device

• PROCESSING– Data must be moved around and manipulated

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Chapter Goals• Components of a von Neumann machine

• Von Neumann fetch-decode-execute cycle– What does “running a program” mean, anyway?

• Limitations of von Neumann architecture

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Chapter Goals• Memory “Pyramid”– Memory has characteristics and trandoffs– Primary vs Secondary memory

• Primary memory organization (RAM)• Secondary memory (auxiliary storage devices)

• Alternatives to von Neumann architecture

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Computer Components

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Motherboard

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WHAT A MESS!!!

We need to ABSTRACT

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We need Some Abstraction!!!

• Real hardware is messy • Especially Intel architecture because of

backward compatibility (aka legacy issues)• We need some simpler models (abstractions)

of von Neumann architecture

Who has been to Disneyland?

Von Nuemann Architecture

• The parts are connected to one another by a collection of wires called a bus

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Figure 5.2 Data flow through a von Neumann architecture

Von Nuemann Architecture

• The bus is SHARED by several devices• This affects how data flows

• ANALOGY:– Who do you call most on your cell phone?– Some devices communicate more than others

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von Neumann Architecture

5-11Figure 5.1 The von Neumann architecture

Main Memory (RAM)

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RAM

• Memory is a collection of cells, each with a unique physical address

• How many data bits?

• How many address bits?

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What is in a CPU??

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CPU

CPU Components

• Arithmetic Logic Unit• Control Unit• Registers

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ALU(does the work)

REG(holds data)

CU(The Boss)

MEMORY program

Arithmetic/Logic Unit

• Performs basic arithmetic operations:– Adding– Multiplying– Dividing

• Performs logical operations such as AND, OR, and NOT– Example: RGB color mixing

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Registers

• Contain the data that the CPU is processing “at the moment”

• There is a set of registers

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Control Unit

• Control unit controls the instruction cycle

• Reads in a SW program, one instruction at a time

• Tells the ALU what to do

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Control Unit

• There are two special registers in the control unit

– The instruction register (IR) contains the instruction that is being executed

– The program counter (PC) contains the address of the next instruction to be executed

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The Fetch-Execute Cycle

The Control Unit makes the CPU go through the following cycle:

1) Fetch the next instruction2) Decode the instruction3) Execute the instruction– the cycle repeats – forever!

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Fetch-Decode-Execute Cycle

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Memory Mixes

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• Computers contain a mix of different kinds of memory

• Why????

• Will it always be this way?

Memory and the Memory Pyramid

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Capacity Cost&Speed

Tape

Magnetic Disk

Cache

Main RAM

Flash RAM

Primary and Secondary Storage

• Primary Storage – aka “Main Memory” (usually RAM)– the “working memory” of the CPU– Fast– High $ per byte

• Secondary Storage – where all the stuff that is not being worked on “now” is stored (usually

DISK)– Slow– Low $ per byte

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Primary Memory - RAM

• RAM stands for Random Access Memory– Any location can be accessed quickly,– Same amount of time to access any location (aka

‘random’)

• RAM is volatile– Data is LOST when the power is turned off

• Primary (Main) memory is – Volatile– Limited– Expensive

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Primary vs Secondary

• Computers have a BALANCE of Primary and Secondary Memory

• Trade offs:– Speed– Size– Cost

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Secondary Memory

• Secondary memory is – Big– Cheap– Slower than Primary Memory

• Examples:– Magnetic Disk– CD Rom– Flash (Solid State Drives)

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Magnetic Tape

• The first truly mass auxiliary storage device was the magnetic tape drive

• Cassette Tapes are still used for large data backups

Figure 5.4 A magnetic tape 5-17

Magnetic Disks

• A read/write head travels across a spinning magnetic disk, retrieving or recording data

Figure 5.5 The organization of a magnetic disk

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Compact Disks

• A CD drive uses a laser to read information stored optically on a plastic disk

• CD-ROM is Read-Only Memory– Approximately 700MB

• DVD stands for Digital Video Disk– Approximately 4 GB

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QUESTION TIME

• Does the PERFECT MEMORY EXIST??

• What would be its characteristics??

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Does anybody have a Solid State Drive (SSD)

??

Von BOTTLENECK

• Von Neumann has a fundamental limitation:

•The SHARED BUS!!

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Alternatives to von Neumann

• Several alternative architectures exist• Some are used to enhance von Neumann• Examples:– Synchronous Processing (Parallel)

– Pipelining (Serial)

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Synchronous processing

• One approach to parallelism is to have multiple processors apply the same program to multiple data sets

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Figure 5.7 Processors in a synchronous computing environment

Some Parallel Architecture Examples

• Google– Many servers in one building (“Server Farm”)

• SETI– Geographically Distributed Processors

• Quad Core and Tilera– Several CPUs on one chip

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Pipelining

• Arranges processors in tandem, where each processor contributes one part to an overall computation

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Figure 5.8 Processors in a pipeline

Pipelining Examples

• Like a manufacturing assembly line (cars)

• Some series of tasks can be pipelined– Example: game video processing

1. Build vector model2. Wrap vectors in bitmaps3. Generate camera view

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