CSC 110 - Intro. to Computing

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CSC 110 -Intro. to Computing

• Lecture 9
• Computing Components

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Announcements

• Homework 1 returned at end of class
• Mean score 80 s15
• Answer key available on web page
• Quiz at end of class on Thursday
• Practice quiz on Blackboard/web (answers on
  separate page)
• Do NOT memorize algebraic properties
• I will provide them

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Working Together

• Goal is for students to learn
• Means mistakes are made, questions raised
• Peers useful when learning material
• But the goal is for YOU to learn material
• Talk about homework all you want
• Leave conversation with only memories, nothing
  written, typed, dictated, displayed on a screen
• Wait at least 15 minutes before continuing with
  homework

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How Does a Computer work?

• When discussing computers, most people think of
  processor
• A.k.a., Central Processing Unit (CPU)
• Examples include Pentium IV, PowerPC, Itanium,
  Pentium M

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What To Execute Next

• Most modern computers use von Neumann
  architecture
• Does not require separate components to store
  data and instructions
• Harvard architecture would require 2 hard drives
• Uses control unit to drive entire machine
• Assumes existence of input output devices

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How a Computer Is Organized
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CPU Design

• Processor is made up of several parts
• These parts serve many functions
• Calculating mathematical logical functions
• Commanding actions of rest of computer

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Arithmetic/Logical Unit

• Calculates mathematical logical actions
• So does addition, subtraction, multiplication,
  division, AND, OR, NOT, NOR
• Accepts only one or two inputs
• a b/c is two instructions an addition and
  division
• Uses small VERY fast memory Registers
• Registers work at speed of processor, much faster
  than any other memory
• Only 16 - 64 registers available on a machine

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Control Unit

• Organizes and oversees program execution
• Also uses several registers
• Instruction Register (IR) holds instruction to
  execute
• Program Counter (PC) states what instruction to
  execute next
• Control unit insures computer executes
  step-by-step in logical, orderly manner
• Often to the chagrin of person using computer

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Memory

• Modern computers typically use 8-bit
  addressability
• 8 bits 2 nibbles 1 byte
• Each memory location stores 1 byte
• Most Intel-based machines use 32-bit address
  space
• Can access at most 232 different bytes
• Or no more than 4,294,967,296 bytes of memory

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Memory continued

• Apple, AMD, and newer Intel-based machines use
  64-bit address space
• How many times more memory is this?
• Why could this be needed?

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Memory

• Modern desktop machines are 32-bit
• Means they access memory 32-bits at a time
• How computers view memory contents

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Memory

• What does the data represent?
• Could be a program, picture, mp3, CSC110 grades,
  
• Processor translates this data into something
  more meaningful
• Output units then present this information

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Output Units

• Output unit A device through which results
  stored in the computer memory are made available
  to the outside world

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Input Units

• Input Unit A device through which data and
  programs from the outside world are entered into
  the computer

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Limitations of Book Division

• What would a hard disk be considered?

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Limitations of Book Analogy

• What would a hard disk be considered?
• Saving this class lecture ? Output Unit
• Loading this lecture ? Input Unit
• Some devices perform both input and output

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Connecting the Computer
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Time versus Space

• Rear Admiral Grace Murray Hopper
• A coil of wire nearly 1,000 feet long
• Distance traveled by an electron along the wire
  in the space of a microsecond
• A 1 foot piece of wire
• In the space of a nanosecond
• The length of a grain of pepper
• In the space of a picosecond

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Bus Operations

• Bus driven at a specific frequency
• Different buses connect different components
• Do not want slow hard drive to work at speed of
  fast memory
• Could have two buses join at one point
• Only one device can write to bus at a time
• Two devices writing at once called a collision
• Sophisticated algorithms used to limit impact

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Executing a Program

• Processors run at 3GHz
• Memory runs much slower
• But memory contains the instructions
• Processor does no good spinning wheels waiting
  for instruction from memory
• How can increasing processor speed be helpful?

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Fetch-Execute Cycle

• Processor run like assembly line
• One stage fetches instruction for memory
• Stores small number of instructions in fast
  memory stored on processor cache
• Next stage decodes the instruction
• Retrieves any data needed from memory
• Data stored in registers

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Fetch-Execute Cycle

• Instruction is executed
• Multiple units execute instructions
• ALU executes math/logic functions
• Control unit handles branch instructions
• Have multiple ALUs to execute multiple
  instructions at once
• Final unit retires instruction
• Writes results back to main memory

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Fetch-Execute Cycle
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Processor Limitations

• Can only push processor so far
• Ultimately limited by speed of electrons
• Running into physical limits of how quickly
  silicon-based gates can switch
• Replacement technology is VERY expensive

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Processor Bottleneck Solution

• Often have data all of which needs same
  transformation
• mp3s, movies, graphic files
• Weather forecasting
• Use fetch-execute cycle
• But execute each instruction on multiple data sets

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Processor Bottleneck Solution

• Used in supercomputers, high-end workstations
• Have multiple processors perform actions
  simultaneously
• Also found in desktop/laptop machines
• Use multiple functional units in single processor
• Called MMX in Windows-based machines, Altivec
  on Macs

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SIMD Processing
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MIMD Processing

• Usually have multiple processes at once
• Using computer to multitask
• Could speed performance by splitting tasks onto
  different CPUs
• Could be done by splitting processor time
• Intels hyperthreading
• Could join multiple CPUs onto one chip
• Becoming more common as we speak

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MIMD Processing
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Secondary Storage

• Main memory is volatile and limited
• Secondary storage vital for long-term data
• Also stores unneeded data
• Need has existed since beginning of computer

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Magnetic Tape

• One of first systems of saving data
• Works in manner identical to audio cassette
• Slow access times
• What are they still used for?

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Magnetic Disks

• Small read/write head flies over platter
• Disk crashes when head contacts platter
• Platter covered in thin film of protective
  material
• Using multiple platters improves performance
• Can access data quicker
• Can improve disk reliability

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Magnetic Disk
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Magnetic Disks

• Head moves directly to location on disk with data
• Disk split into many tracks
• Like CD or record
• Each track split into sectors
• Each sector stores one block of data
• All blocks contain same amount of data

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For Next Lecture

• Read PALGO chapters 1-5
• First real work directing computers
• What I find most fun about computers
• Study up on circuits
• Quiz at end of next lecture
• Get ready for homework on computing components
  next week