The%20Components%20of%20the%20System%20Unit

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The Components of the System Unit
Chapter 4

• Jeremy Lukianovich

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The system unit

• The system unit is the case that contains the
  electronic components that make up a computer.
• The mother board is the main circuit board that
  all of the electronic components are in some way
  connected to.

3
Computer Chip

• The computer chip is a small piece of etched
  semi-conducting materiel, such as silicone.
• There are two types of attachments
• 1) DIP-dual inline package (two rows of metal
  feet)
• 2) PGA-Pin grid array (large number of pins
  covering the surface of the chip)

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Processor-(CPU)

• The Control unit- directs and coordinates
  activities in the computer
• The arithmetic logic unit- performs comparisons,
  arithmetic, and logic operations
• Machine cycle- the repeated 4 steps to all
  computer actions (1-fetching, 2-decoding,
  3-executing, 4-storing)
• Registers-Small storage locations in the
  processor. This is a high speed temporary
  storage area.
• The system clock- controls timing of all computer
  operations

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• Processor installation and upgrades
• Three types
• Chip for Chip-Replace existing chip
• Piggy back-stack new one on top of old chip
• Daughterboard upgrade-new chip on adapter card
  that plugs into motherboard
• Heat sinks and heat pipes
• ceramic or metal finned components that help
  dissipate heat
• Coprocessors
• a secondary chip that aids the main processor,
  thereby increasing the performance of the
  computer
• Parallel processing
• Using multiple computer processors to increase
  the speed of the processor.

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Data Representation

• Computers use digital representation
• Binary code
• 1on
• 0off
• A single digit is a bit
• 8 bits equal a byte
• Two coding systems
• ASCII
• EBCDIC

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Memory

• RAM (Random access memory)
• Primary memory type
• Read from and written by programs
• If power loss RAM is lost, unless stored
• DRAM (Dynamic RAM)
• Must be reenergized or will lose memory
• Several types
• SRAM (Static RAM)
• Most stable but expensive
• More RAM the faster the computer will be

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• Cache
• Memory Cache
• Stores frequently used data - speeds up computer
• 3 types
• L1-built into processor
• L2-advanced transfer cache
• L3-separate cache, must have L2 to work
• Disk Cache (see chapter 7)
• ROM (Read only memory)
• Stores permanent data and instructions
• Flash memory
• Nonvolatile memory that can be erased
  electronically
• Often contains startup instructions due to its
  adaptability
• CMOS (Complimentary metal-oxide semiconductor)
• Technologically advanced materiel that produces
  high speeds with low power draws.
• Memory access times
• The time it takes a computer to do an operation,
  this can be as little as 10 nano-seconds

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Expansion Slots and Adapter cards

• Expansion slots
• Slot on computer that can hold a circuit board
  that in some way increases the performance of the
  computer.
• Sound cards
• Video cards
• Modem cards
• Network cards
• PC cards and Flash memory cards
• PC cards-a thin device that plugs into a computer
  and adds memory, storage, sounds, modem,
  communications, fax, or other abilities to the
  computer.
• Flash memory cards-a card that allows a user to
  add data from a mobile device (such as a PDA) to
  a laptop.

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Ports and connectors

• Serial ports-a port that connects two devices and
  transmits 1 bite at a time, good for devices that
  do no require high transfer rates.
• Mouse
• Keyboard
• Modem
• Parallel ports-a port connects devices but
  transmits data at a higher rate than a serial
  port
• Printers
• USB ports-universal serial bus port
• Can connect up to 127 peripherals together on one
  port.
• Daisy chain them
• USB hub
• Hot plugging (plugging in a device without first
  shutting the computer down.

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Special purpose ports

• Firewire port
• Similar to USB
• Faster than USB
• MIDI port (musical instrument digital interface)
• Used to connect a instrument to a computer
• SCSI (small computer system interface
• Attach such devices as disk drives and printers
• Daisy chain up to 7 to 15 devices
• IrDA (infrared data ssociation)
• Transfer data via infrared light waves,
  completely wireless
• Bluetooth
• Radio waves to transmit information
• Similar to IrDA but you dont need to line up the
  devies

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Buses

• Buses
• The channels within a computer chip which the
  bits take to travel from one point to another.
• Bus width dictates how many bits a computer may
  transmit and one time
• Faster the bus speed the faster the programs will
  run.
• System Buses
• Part of the mother board
• Connects processor to main memory
• Expansion buses
• Channels outside the main processor that transmit
  data into and out of the processor
• ISA (industry standard bus)-slowest
• Local- high speed bus that connects things such
  as disk drives
• Accelerated Graphics port-improves speed which 3D
  graphics move
• USB and Firewire
• PC Card bus

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Bays

• Opening in system where you can insert additional
  equipment
• Drive bays- rectangular openings which usually
  house disk or CD drives.

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Power Supplies

• Battery powered-primarily laptops
• AC adaptor-allows the DC powered computer to be
  plugged into a AC power supply (wall socket)
• A cooling fan is generally mounted near the power
  input

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Mobile Computers and Devices

• Laptops-small computers that have folding
  screens, very portable
• Contain many miniaturized components which
  generally raises the price
• Tablet PC-entire computer in the shape of a
  tablet.
• PDA-handheld computing device, generally contain
  a phone book, basic word processing, and little
  else.