Unit 2. Hardware Systems

1
Unit 2. Hardware Systems

• 2.1 Processor and Memory
• 2.2 Peripherals
• 2.3 Storage devices
• 2.4 Putting Together the Hardware Components
• 2.5 Improving Computer performance

2
Overview of Hardware Components
Microprocessor (executes instructions)
Chipset (controls data flow)
Main Memory (temporarily stores data and
program instructions while the computer is
running)
Storage Devices (permanently store data and
application programs)
Legend
Peripherals (input/output)
Components
Data Path
3
How a File is Displayed

• The microprocessor sends instructions to the
  storage devices (via the chipset) requesting the
  specified file to be loaded into main memory.
• The storage devices send the file through the
  chipset to main memory.

• The microprocessor fetches
• the file contents from main
• memory.
• The microprocessor sends the display data to the
  monitor
• via the chipset.

4
Components inside the System Unit
A. Motherboard
H. Disk drives
B. Power supply
C. Microprocessor (underneath a cooling fan)
G. IDE cable
D. Expansion slot
E. Expansion card
F. Chipset
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Fetch-Execute Cycle
Control Unit
Step 1. Control unit fetches instruction
Step 3. Control unit executes the instruction by
directing the ALU to add the 2 numbers in the
registers 1 and 2 then store the result in the
accumulator.
Step 2. Control unit interprets the instruction
and sends the 2 numbers to be added into the
appropriate registers in the ALU.
Step 4. Result is stored back in memory.
ALU
Register 1 (contains Number 1)
Register 2 (contains Number 2)
Accumulator (Result of Number 1 Number 2)
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The Microprocessor
Microprocessor
Chipset (controls data flow)
Main Memory (temporarily stores data and
program instructions while the computer is
running)
Storage Devices (permanently store data and
application programs)
Legend
Peripherals (input/output)
Components
Data Path
7
Processor Performance

• Rate at which the instructions are processed
  (clock rate)
• Measured in Hertz
• 1 Hertz - one cycle per second
• Processor clock rate measured in MHz
• Machines are compared based on their clock speed
  or number of instructions per second (ISP).
• This measure depends on both the number of cycles
  per second and the mix of instructions executed.
• Measure of processor performance is benchmarking.
• ZDNet is organization which has a set of useful
  benchmarks

8
Types of Memory
Main Memory
Microprocessor (executes instructions)
RAM (instructions to be executed after computer
is booted)
Boot Memory
ROM (instructions needed to boot the computer)
Chipset (controls data flow)
Storage Devices (permanently store data and
application programs)
CMOS (Configuration information used in the boot
process)
Legend
Peripherals (input/output)
Components
Data Path
9
Types of Memory (continued)

• RAM (random access memory) is a temporary holding
  area for both data and instructions. It is also
  referred to as main memory.
• Data in RAM is lost when the computer is turned
  off.
• Measured by its memory capacity and latency.
• Capacity is the maximum number of bits or bytes
  that can be stored. The capacity of RAM is
  typically measured in megabytes (MB). Many
  computers have RAM capacity of 128MB or more.
• Latency is the delay between the time when the
  memory device receives an address and the time
  when the first bit of data is available from the
  memory device. This delay is also referred to as
  access time. Latency is typically measured in
  nanoseconds (ns), billionth of a second (10-9
  sec). Latency measures the speed of RAM.

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DRAM

• DRAM - Dynamic RAM is a common type of RAM.
• Made of an integrated circuit (IC), composed of
  millions of transistors and capacitors.
• A capacitor can hold electrons. An empty
  capacitor represents a zero, and a non-empty
  capacitor represents a one. Each capacitor can
  register either a zero or a one for a memory
  cell, storing one bit of data.
• The transistor is like a switch that controls
  whether the capacitor's state (charged or not
  charged, 1 or 0) is to be read or changed.
• However, a capacitor is like a cup that leaks, in
  order to keep its charge, the memory control
  needs to be recharged or refreshed periodically.
  Therefore, it is called the dynamic RAM because
  its state is not constant.
• Refreshing capacitors also takes time and slows
  down memory.

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DRAM (continued)

• SDRAM (Synchronous Dynamic RAM)
• Used in many personal computers
• Fast and relatively inexpensive
• Synchronized to the clock so that data can be
  sent to the CPU at each tick of the clock,
  increasing the number of instructions the
  processor can execute within a given time
• DDR SDRAM (Double Data Rate SDRAM)
• Transfers twice the amount of data per clock
  cycle compared to SDRAM
• Capacity is up to 2 GB
• RDRAM (Rambus Dynamic RAM)
• Higher bandwidth than SDRAM
• More expensive compared to SDRAM
• Enhances the performance of applications that
  access large amounts of data through memory, i.e.
  real-time video and video editing
• SRAM (Static RAM)
• Uses transistors to store data
• Because SRAM does not use capacitors, reading
  data from SRAM does not require recharging the
  capacitors. Therefore, it is faster than DRAM.
• Holds fewer bits and costs more compared to DRAM
  of the same size
• Used in the cache because it is fast and cache
  does not require a large memory capacity

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RAM Comparisions
13
Which Memory Device to Use?
ROM
no
Need to maintain data when power is off?
Need to update information?
Need to store configura-tion information?
yes
no
Start
no
yes
yes
EEPROM/ Flash
RAM
CMOS
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Processor and Memory
Microprocessor
Main Memory
CPU (ALU, Registers, Control unit)
RAM (instructions to be executed when the
computer is running)
L1 cache
L2 cache (usually on CPU)
Boot Memory
ROM (instructions needed to boot the computer)
Storage Devices (permanently store data and
application programs)
Chipset (controls data flow)
CMOS (Configuration information used during the
boot process)
Legend
Peripherals (input/output)
Components
Data Path
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Peripherals
Storage Devices
Microprocessor (executes instructions)
Storage Devices (permanently store data and
application programs)
Main Memory (temporarily stores data and
program instructions while the computer is
running)
Chipset
Peripherals
Legend
Parallel
modem
Component
PS-2
sound card
Memory
Port
PCI Slots
Expansion Card
video card
USB
Expansion Slot
FireWire
AGP Slot
Peripheral Device
Digital camera
Camcorder
Monitor
Modem
Printer
Bus
Mouse
Speaker
Scanner
Disk drive
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Expansion Slot, Card, and Port

• An expansion slot is a slit-like socket on the
  motherboard into which a circuit board can be
  inserted.
• The circuit board is called the expansion card.
• Used to extend the capability of a computer
• Examples sound card and the video card
• Also provides port(s), which are connector(s)
  between the expansion card and the peripheral
  device.

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Expansion Slots

• The two most common types of expansion slots are
  Peripheral Component Interconnect (PCI) and
  Accelerated Graphics Port (AGP).
• PCI (Peripheral Component Interconnect ) slot
• Can hold a variety of expansion cards such as a
  sound card or an Ethernet card
• AGP (Accelerated Graphics Port) slot
• Primarily used for graphics cards
• PCMCIA (personal computer memory card
  international association) slot
• Used for laptops in place of PCI slots on desktop
  computers
• Relatively smaller than a PCI slot

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Expansion Cards

• Small circuit boards that control the peripheral
  devices
• Graphics Cards
• Takes signals from the processor and displays the
  graphics, images in the monitor
• Sound Cards
• Converts analog sound signals to digital and vice
  versa
• Modem
• Transmits data over phone or cable lines
• Ethernet card
• Serves as the interface to a Local Area Network
  (LAN), a common network technology allowing users
  access to network resources such as the Internet,
  email, shared printers, etc.
• Transfers data at a rate of 10 Mb/s
• Newer versions of Ethernet called "Fast Ethernet"
  and "Gigabit Ethernet" support data rates of 100
  Mb/s and 1 Gb/s (1000 Mb/s).

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Expansion Ports

• Ports are connectors that enable signals to be
  passed in and out of a computer or peripheral
  device.
• Cables from peripheral devices connect to ports
  of a computer system.

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Different Types of Ports

• PS/2 port, also known as serial port
• Transfers data one bit at a time
• Uses a 6-pin, mini-DIN configuration, which look
  like a small, round port
• Used to be the de facto standard for keyboard and
  mouse connections, however, they are gradually
  being replaced by USB ports.
• DB-9 port
• Also becoming obsolete
• Used to connect PDA devices before the advent of
  USB ports
• Connects external modem, barcode scanner, and
  other older electronic devices
• DB-25F, also known as Parallel port
• Transfers data one byte at a time
• Requires a 25-pin male connector (DB-25M) on the
  cable
• Can be used for printers or external drives

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USB and FireWire

• USB (Universal Serial Bus) port
• Appears on desktop systems and laptops
• Can connect up to 127 devices via a USB hub,
  which provides multiple USB ports (e.g. mouse,
  keyboard, scanner, printer, digital camera, and
  hard disk drive)
• Supports "hot connectivity," which allows
  peripherals to be connected to the system,
  configured, and used without restarting the
  machine
• Replacing serial and parallel ports
• FireWire
• Faster data transfer rate and more expensive
  compared to USB (50MBps versus 1.5 MBps)
• Supports up to 63 devices
• Intended for data-intensive devices such as DVD
  players and digital camcorders
• Peripheral devices can be connected via chaining.
  
• Supports hot connectivity
• Note In response to FireWire's fast data
  transfer rate, USB-2 is developed with a data
  transfer rate of 60 MBps. To compete with USB,
  FireWire 2 is developed with a data transfer rate
  of 100 MBps.

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Comparing Different Ports
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Buses
Microprocessor (executes instructions)
Storage Devices
F r o n t
s i d e
Storage Devices (permanently store data and
application programs)
Main Memory (temporarily stores data and
program instructions while the computer is
running)
Chipset
PCI
Memory
PC I
AGP
USB
F i r eWi r e
Peripherals
Legend
Parallel
modem
Component
PS-2
sound card
Memory
Port
PCI Slots
Expansion Card
video card
USB
Expansion Slot
FireWire
AGP Slot
Peripheral Device
Digital camera
Camcorder
Monitor
Printer
Phone line
Bus
Scanner
Mouse, keyboard
Speaker, microphone
Disk drive
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Bus

• A bus is a pathway through which data is
  transferred from one part of a computer to
  another.
• Consists of the data bus and the address bus.
• The data bus transfers the data itself, while the
  address bus transfers information about where the
  data is to go.
• Has a width, a speed, and a transfer rate.
• The width, also called the word size, of a bus is
  measured in bits.
• The speed of a bus is measured in hertz (Hz), or
  cycles per second.
• Transfer rate is the measure of how much data may
  be moved from one device to another in one
  second.
• Transfer rate can be increased by transferring
  data multiple times during a cycle or increasing
  the number of channels used to transfer data.

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Different Types of Buses

• Front Side bus
• Bus on the motherboard that transfers data
  between the CPU and the chipset
• Memory Buses RAM bus and DRAM bus
• Usually transfers data multiple times during a
  clock cycle or uses multiple channels to transmit
  data to increase data transfer rate to match that
  of the CPU.
• ISA (Industry Standard Architecture)
• Becoming obsolete
• Word size or width of the data path is 16 bits,
  running at a mere 8 MHz
• PCI (Peripheral Component Interconnect)
• Predominant bus for newer systems
• 32 bits (standard), running at 33 MHzgiving PCI
  up to 133MBps of bandwidth
• AGP (Accelerated Graphics Port)
• Bus architecture similar to that of PCI
• Provides video cards with rapid access to the
  system memory
• To date, only used for graphics cards, especially
  those that perform texture-mapping onto
  three-dimensional renderings
• Very fast, running at 66 MHz with a 32-bit word
  size, and transferring 266 MBps

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Different Types of Buses (continued)

• IDE bus
• Transfers data between storage devices and the
  chipset
• USB (Universal Serial Bus) and FireWire (IEEE
  1394)
• Transfer data one bit at a time at a variable
  pace
• Not rated with a MHz speed rated by peak
  transfer rate.
• USB
• Faster than standard serial connections, with a
  peak transfer rate of 1.5 MBps.
• Considered a low-speed bus and is designed to
  handle low to medium-speed peripherals
• An extension to USB-1 is USB-2, which supports
  data rates up to 60 MBps versus the 1.5 MBps in
  USB-1 USB-2 is fully compatible with USB-1.
• FireWire
• High transfer rate designed for high-speed
  external peripherals such as DVD-ROM and hard
  disk drives
• FireWire 2 (IEEE 1394b) emerged with data rates
  up to 100 MBps, double that of FireWire 1 (IEEE
  1394).

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Input Devices

• Cameras
• Digital Camera
• Enables photos taken to be stored in digital
  form, which can uploaded onto a computer.
• Web Camera (webcam)
• Captures live video and sends the compressed
  image stream to the computer or to other
  computers via the Internet
• Digital Camcorders
• Record video in digital form, which can be
  uploaded onto a computer without further loss in
  image quality
• Recorded video can be edited using movie-editing
  software
• Images are more clear than those captured by a
  webcam, but requires more bandwidth
• Uses fireWire jack/interface to enable host
  computers to provide enough bandwidth for the
  camcorder
• Scanners
• Convert a 2-D physical image (for example, a
  photograph or a paper copy of an image) into a
  digital image that can be viewed and edited on
  your computer

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Output Devices Monitors and Projectors

• CRT (cathode ray tube) monitors
• Used to be the most common type of computer
  monitors until LCD monitors began to gain
  popularity
• Use three electron beams to create colors, red,
  green, and blue. To generate the color white, all
  three beams are fired simultaneously. To create
  the color black, all three beams are turned off.
  Other colors are created using different mixtures
  of these three color beams.
• Inexpensive and dependable for displaying images
  on screen.
• Also found in conventional TV sets.
• LCD (liquid crystal display) monitors
• Produce images by manipulating light within a
  layer of liquid crystal cells
• Also known as flat-panel screens
• Compact, lightweight, easy-to-read, and emit less
  radiation compared to CRT monitors
• Used in notebook computers and desktop computers

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Projectors

• Enable images on the computer screen to be
  magnified and projected onto a bigger screen
• Use two types of technologies
• LCD (liquid crystal display) system
• Images are projected as light shines through a
  layer of liquid crystal cells
• DLP (digital light processing) system
• Uses tiny mirrors that reside on a special
  microchip called the Digital Micromirror Device
  (DMD)
• Images are smoother and have better contrast than
  those created using LCD

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Printers

• Ink Printers
• Works by spraying and dyeing the page with color
• Rated according to their resolution and color
  depth
• Color depth is the range of colors that any given
  drop may represent
• Resolution is measured in dpi, the number of dots
  per inch (horizontally or vertically) that a
  printer can place on a page. Sometimes the dpi is
  the same both horizontally and vertically, such
  as 1200 dpi. Other times, the horizontal and
  vertical dpi differas in1440x720 dpi.
• Use a four-color process, CMYK (cyan, magenta,
  yellow, and black), to produce various colors.
  Sometimes the color black is excluded because it
  can be produced by mixing the other three colors.
• Multiple drops of colors can also be placed on a
  single dot to produce more colors.

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Printers (continued)

• Dye-Sublimation Printers
• Used to print high-quality images like those at a
  photo lab
• Use solid dyes consisting of the four colors,
  cyan, magenta, yellow, and black.
• Varying mixtures of CMYK color dyes can be used
  to represent different colors, achieving
  photo-like quality
• The print head heats and vaporizes the dyes to
  allow them to permeate the glossy surface of the
  printing paper before they solidify
• Laser Printers
• Use toner cartridges that contain toner, a
  colored powder
• Uses laser beams to charge the image of the page
  onto a photoelectric drum
• When the paper runs through the printer in
  between the drum and the toner cartridge, the
  electro-magnetic charge of the drum picks up the
  toner and then transfers it to the paper. A heat
  and pressure system then fuses the powder to the
  page.

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Disk Controller Interfaces
Microprocessor (executes instructions)
Storage Devices
Storage Devices
Hard drive
Disk Controller
I D E
CD-ROM
Main Memory (temporarily stores data and
program instructions while the computer is
running)
Chipset (controls data flow)
PCI
DVD-ROM
Legend
Peripherals (input/output)
Components
Data Path
Bus
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IDE Interface

• Provides a standard way for storage devices to
  connect to a computer
• The controller for the IDE is usually integrated
  into the disk or CD-ROM drive, and the controller
  directs how the hard drive stores and accesses
  data.
• IDE was created as a way to standardize the use
  of hard drives in computers by combining the
  controller and the hard drive because having
  separate controllers and hard drives resulted in
  poor signal quality and performance.
• In 1984, IBM introduced the AT computer with a
  hard drive had a combined drive and controller. A
  ribbon cable from the drive/controller
  combination is used to connect to the system
  unit, creating the AT Attachment (ATA) interface.
  
• Soon, other vendors started offering IDE drives
  based on the ATA standard developed by IBM. Thus,
  IDE became the term that covered the entire range
  of integrated drive/controller devices. Because
  almost all IDE drives are ATA-based, the two
  terms are used interchangeably.

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EIDE

• EIDE is Enhanced IDE.
• Provides a set of two IDE (Integrated Device
  Electronics) ports. 
• Primary port and secondary port
• Each port attaches to a cable containing two
  plugs, and each plug can connect to a device.
• Total of four devices can be accommodated two on
  the primary, and two on the secondary.

Primary Master Device
Primary IDE Port
Primary Slave Device
Secondary Master Device
Secondary IDE Port
Secondary Slave Device
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Mass Storage

• Slowest access times
• Low transfer rates
• Located farther from processor
• Examples
• Magnetic disks (Hard discs, floppy discs)
• Optical disks (CD-ROM)
• Magnetic tapes
• Advantages of Mass storage devices
• Non-volatile (data remains even after power is
  turned off)
• High storage capacity (billions or trillions of
  bytes)
• Cost per bit is lower than RAM
• Use removable media in some cases

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MTBF (Mean Time between Failures)

• Reliability of the computer component is
  expressed as MTBF
• Calculated by dividing the number of failures by
  the total hours of observation.
• MTBF is somewhat misleading to most consumers.
• Effect of Hardware depends on the component
  fails.
• If RAM , monitor or microprocessor fails they can
  be replaced.
• Hard Disc drive failure is serious as all the
  data are lost.

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Optical Media CDs and DVDs

• Advantages of optical technologies
• Reliability they are less prone to environmental
  damages.
• Usually used as a medium for multimedia
  presentations that combine sound with graphics,
  such as movies
• A DVD is an enhanced form of a CD.
• The two types of disks are physically the same
  size, but they differ in format.

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DVDs

• Greater capacity
• Narrower tracks
• Use blue laser, which has a shorter wavelength
  than the red laser used by CDs, allowing it to
  focus on the tinier tracks of the DVD.
• Use multiple layers of tracks
• Blue laser beams can penetrate the plastic and
  focus at different depths
• Some are dual-layered- two sets of tracks on one
  side of the disk, one beneath the other. This
  doubles the capacity of one side of a DVD disk.
• A double layer double side (DLDS) DVD drive uses
  double layers and can read double-sided disks,
  giving it four times the capacity of a single
  layer single side (SLSS) drive.

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CDs

• Two recordable formats, CD-R and CD-RW
• Less expensive and have less capacity than a DVD
• Most expensive of the CD drives, are priced about
  the same as a read-only DVD drive.
• The more capable DVD-RW drives can be four times
  the cost of a standard DVD drive.
• Many computers (desktops and laptops) today are
  equipped with CD-RWs and read-only DVD combo
  drives.

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Magnetic Media Zip Disks

• Magnetic media range from some of the smallest
  capacity storage devices, floppy disks, to the
  largest capacity devices, hard disk drives.
• Zip disks
• Removable storage drives produced by Iomega,
  allow users to store much larger amounts of data
  than a floppy disk can hold
• Capacity ranges from 100 to 750 MB
• Better option for graphics and large files.
• Were once very popular, and many machines can
  still be purchased today with a Zip drive as
  standard equipment. But, their use declined with
  the wide availability of CD-RW drives and the
  reduced cost of blank CD-R disks.

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Optical Versus Magnetic Media

• Optical Media
• more durable not ruined by dust or moisture,
  nor are they vulnerable to electrical damage
  (however, they can be damaged by physical damages
  such as scratches).
• MTBF rating (average life expectancy) ranges
  between 30 and 300 years, while magnetic media
  utilize magnetic properties that have a MTBF of
  about 37 years.
• Magnetic Media
• Less expensive per MB than magnetic disks
• Can be written and read faster than optical disks
  (except for floppy disks)
• Most hard disk drives offer greater capacity than
  any currently available optical device

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Solid State

• Solid-state memory, or flash memory, uses no
  moving parts inside the chip.
• Records data using electronic charges
• Rewrites data by applying electric fields using
  in-circuit wiring to erase predetermined sections
  of the chip so those areas can be rewritten
• Examples CompactFlash and SmartMedia cards.
• CompactFlash card
• Uses a controller chip, which can increase
  performance on devices with slow processors and
  flash-memory chips.
• Storage capacity is between 4MB and 4GB
• SmartMedia card
• Smaller and thinner than a matchbox
• Storage capacity is between 2MB and 256MB

43
Working Together
Main Memory
Microprocessor
CPU (ALU, Registers, Control unit)
Storage Devices
Storage Devices
RAM (instructions to be executed when the
computer is running)
L1 cache
L2 cache (usually on CPU)
Hard drive
Boot Memory
F r o n t
s i d e
ROM (instructions needed to boot the computer)
Disk Controller
I D E
CD-ROM
Chipset
CMOS (Configuration information used during the
boot process)
PCI
DVD-ROM
Memory
Legend
PC I
AGP
USB
F i r eWi r e
Peripherals
Parallel
Component
modem
PS-2
Memory
sound card
Port
Expansion Card
PCI Slots
video card
Expansion Slot
USB
FireWire
AGP Slot
Peripheral Device
Digital camera
Camcorder
Monitor
Phone line
Printer
Bus
Disk drive
Mouse, keyboard
Speaker, microphone
Scanner
44
Major Hardware Components and Their Functionality

• CPU executes instructions stored in memory
  devices.
• During the boot process, the CPU fetches
  instructions from the permanent memory devices,
  ROM and CMOS.
• ROM is read-only memory that stores instructions
  needed to start up the computer.
• CMOS contains system configuration data.
• Once the computer is booted, RAM is used to load
  the rest of the instructions to be executed by
  the CPU.
• Data from storage devices such as the CD-ROM
  drive and the hard drive are passed through the
  disk controller. Data can also be stored on hard
  disk or CD.
• Data in the hardware system passes through buses.
  The buses are the communication channels among
  components in the system unit.
• Peripheral devices such as the keyboard, mouse,
  joystick, printer, speakers, and microphone are
  connected to the computer via ports typically in
  the back of a system unit.
• Expansion cards can be plugged into the expansion
  slots of the computer to extend the functionality
  of a computer.

45
How Components Work Together

• When a computer processes requests from the user,
  the CPU directs the other components to carry out
  specific tasks, and data is passed among
  components through buses and the chipset.
• Scenarios
• To save a file to hard disk, the CPU would pass
  the data to be saved through the front bus to the
  chipset. The chipset sends the file data via the
  PCI bus to the disk controller, which would then
  send the data to the hard disk storage device.
• To open and display an image file, the CPU would
  signal the disk controller to fetch the image
  file on the storage device using and store it in
  RAM. The graphics card would then access the
  image data and display the image as pixels on the
  computer monitor.

46
Researching a Computer System

• Researches done through product reviews
• Price comparisons
• Price and comparisons can be found at
  http//www.cnet.com

47
Online Configuration

• Computer hardware vendors have their own web
  sites
• Sites specify system configurations of various
  products
• Priced by components

48
Moores Law

• Law can be stated as
• Number of transistors on a microchip doubles
  every 18 months.
• Denser the chip gt Higher the capacity
• Limitations Chips must be thick enough for the
  electrons to pass through.
• Predictions based on Moores Law
• Processing power (speed) doubles every 18 months.
  
• Storage capacity of RAM increases exponentially.
• Other observations
• Storage capacity of hard disk drives is also
  increasing exponentially.
• Cost for consumers to purchase computer parts is
  decreasing over time.

49
Moores Law (continued)
50
Parkinsons Law of Data

• Parkinson's Law of Data Data expands to fill
  the space available.
• As more memory or disk space becomes available,
  the demand for more memory or disk space
  increases accordingly.
• As Parkinson's Law predicts, today's operating
  systems are much more elaborate and require more
  memory for their own use.
• As disk drive capacity increases, people begin
  using them in new ways (e.g. storing musical
  recordings, short video clips, and movies).

51
Bottlenecks

• Bottleneck is a step within a series of steps
  that takes the longest time to complete.
• Time required to perform a task consisting of
  several steps may be delayed by the bottleneck
  step.
• Process time cannot be shortened without speeding
  up the bottleneck.
• Typical bottlenecks
• Cache
• RAM
• I/O
• Video card (particularly for 3-D gaming)
• To speed up performance of a system
• Use profiling tools to measure each sections
  time taken to complete to determine the
  bottleneck steps
• Improve upon the bottleneck steps

52
Data Compression

• Storing data in a format that requires less space
  than usual
• When data is compressed, the file size shrinks.
• Amount of shrinkage is referred as compression
  ratio.
• Some compression techniques require specialized
  computer hardware.
• Hardware or software used to compress and
  decompress is technically referred as codec
  (Compressor and Decompressor).

53
Disk Compression

• Disk compression shrinks the files and places it
  in a special volume on the hard disk.
• Disk volume is a disk or an area of a disk which
  has a unique name and is treated as a hard disk.
• Disk compression creates a compressed volume
  containing data that has been re coded to use
  storage space more efficiently.
• Advantages
• Gain storage space without any additional
  hardware.
• Under optimal circumstances, the hard disk
  capacity is doubled.
• Disadvantages
• If the compressed files are no longer required,
  drive space should be sufficient to hold the
  uncompressed data.
• File error in the compressed volume means the
  loss of all the data in that volume.

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File Compression

• Shrinks one or more into single smaller file.
• Compressed file cannot be used until it is
  uncompressed.
• PKZIP and WinZip are popular shareware programs
  that compress and uncompress files.
• Compressing a file is called Zipping.
• Uncompressing a file is known as Unzipping.

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Text File Compression

• Adaptive Pattern Substitution
• Designed specifically for compressing text files.
• Scans the entire text and looks for patterns of
  two or more bytes, substitutes a byte pattern and
  make a dictionary entry for it.
• Effectiveness of the Adaptive Pattern
  Substitution depends on the content of the
  document.
• Another type of compression scans and finds
  repeated words.
• Occurrences of the word is substituted with
  number and it acts as a pointer to the original
  occurrence

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Graphics File Compression

• Run Length Encoding is a technique that looks for
  patterns (i.e.)blocks of same color.
• Graphics file with .tif ,.gif, .pcx and .jpg
  contain bitmap images that have already been
  stored in compressed formats.
• Graphics software used to open and save files
  contains codes required to compress and
  decompress them.
• Compressed file Formats use
• Lossy Compression
• Lossless Compression
• Lossy Compression throws away some of the
  original data for the graphic
• For Example JPEG(Joint Photographic Experts
  Group)
• Lossless Compression provides a way to
  reconstitute all of the original data in a
  graphics file.

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Video File Compression

• Used to display video on the PC by
• Reducing number of frames displayed per second.
• Number of frames per second affects the
  smoothness of the video.
• High quality video displays 30 frames/sec and low
  quality 10-15/sec
• Reducing the size of the video widow.
• Displaying an image 1/4 of the screen requires
  only 1/4 of the data required to display on a
  screen.
• The above technique is Intra frame Compression
• Coding only the changes that take place one frame
  to next
• difference between frames are evaluated and the
  data changed are stored.
• The above technique is termed as motion
  compensation.

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Music File Compression

• MP3 is a popular format for music compression
• Type of lossy compression technique as it filters
  the data outside the human hearing.
• Maintains a high degree of sound quality.
• Downloaded MP3 music files from web can be played
  using MP3 software.
• MP3 ripper software is used to convert songs from
  the CD to WAV files.

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END of Unit 2