Topic 6: Further System Fundamentals

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Topic 6 Further System Fundamentals
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Fetch-Execute Cycle Review

• Computer programs are instructions stored in RAM
• Processor fetches instructions and executes them
• Fetch
• Decode
• Execute
• Memory (store results)
• Repeat!

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CPU Diagram
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Additional CPU Components

• Program counter (PC)
• Holds the address of the next instruction in the
  program sequence
• Instruction register
• Holds the operation code of the type of
  instruction to be executed (e.g. ADD, SUB)
• Accumulator
• ALUs internal register that holds ongoing total

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Fetch-Execute Again

• Fetch instruction from the address stored in the
  program counter
• Store instruction in instruction register
• Decode instruction register
• Execute operation (control unit tells ALU what to
  do)
• ALU performs operation and uses its accumulator
  to remember result
• Store accumulator result back to memory

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Interrupts

• Things that interrupt the processors normal
  operation
• Handle events and exceptions
• Keyboard input
• Null pointer exception
• etc.
• Special code exists to handle instructions, which
  is also stored in RAM

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Interrupt Register

• Stores the offset address of the special
  interrupt handling code
• Interrupt Code Address Base Address Interrupt
  Register

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Bus Review

• Bus set of parallel wires
• Brings data from one place to another place
• CPU ?? cache ?? RAM
• address bus ?
• data bus ?

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Hard Drives

• read/write head
• The part of the arm that touches the disk to
  read/write
• block size
• Number of bytes that are read/written in a single
  read of write operation
• track
• Ring around a disk platter
• cylinder
• The set of corresponding tracks from all platters
• sector
• Section of a track

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Disk Latency

• What are the two moving parts of a disk?
• Platter spinning around rotational delay
  (sector wait time)
• Arm w/ head moving across platter (track seek
  time)
• How long does it take to access something on the
  disk?
• Access time track seek time sector wait time

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Operating System

• Controls operation of the computer system
• OS functions
• Input/Output control
• File management
• Resource management (CPU, memory)
• Security
• User interface

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Linker, Loader, Library Manager

• Linker
• Links compiled object code modules
• E.g. import java.io. is linked to your program
• Loader
• Loads linked object code into memory to run
• Library Manager
• Manages library functions used by linker

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More Network Stuff

• Modes of communication
• Telephone lines dialup
• Coaxial cable cable internet
• Twisted pair ethernet
• Fiber-optic FIOS
• Microwave (high frequency radio) wifi
• Satellite

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Packet Switching

• Break data up into packets transmit
• Individual packets are not all necessarily
  transmitted through the same links
• Each packet travels over the best available link
  at the time
• Packets may arrive at destination out of order ?
  must be re-ordered and reassembled (protocol!)

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Network Security

• User logins
• Must be an authenticated user to login
• Password, smartcard, fingerprint, iris, etc.
• Layered access via permissions
• Different levels of user access
• Firewall
• Inspect and filter incoming traffic
• Encryption
• Encrypt data so that it is unreadable by outsiders