Hardware, Wake-up Process, Boot-Up, Operating System Control of Hardware

1
Hardware, Wake-up Process, Boot-Up, Operating
System Control of Hardware

• Dr. Harold D. Camp
• IT 212 002
• 1 February 2007

2
PC Hardware
3
Personal Computer Hardware

• A typical pc consists of a case or chassis in
  desktop or tower shape and the following parts
• Motherboard or system board with slots for
  expansion cards and holding parts Central
  processing unit (CPU)
• Computer fan - used to cool down the CPU
• Random Access Memory (RAM) - for program
  execution and short term data storage, so the
  computer does not have to take the time to access
  the hard drive to find the file(s) it requires.
  More RAM will normally contribute to a faster PC.
  RAM is almost always removable as it sits in
  slots in the motherboard, attached with small
  clips. The RAM slots are normally located next to
  the CPU socket.
• Basic Input-Output System (BIOS) or Extensible
  Firmware Interface (EFI) in some newer computers
• Buses
• PCI
• PCI-E
• USB
• HyperTransport
• CSI (expected in 2008)
• AGP (being phased out)
• VLB (outdated)
• ISA (outdated)
• EISA (outdated)

4
Personal Computer Hardware

• Power supply - a case that holds a transformer,
  voltage control, and (usually) a cooling fan
• Storage controllers of IDE, SATA, SCSI or other
  type, that control hard disk, floppy disk, CD-ROM
  and other drives the controllers sit directly on
  the motherboard (on-board) or on expansion cards
• Video display controller that produces the output
  for the computer display. This will either be
  built into the motherboard or attached in its own
  separate slot (PCI, PCI-E or AGP), requiring a
  Graphics Card.
• Computer bus controllers (parallel, serial, USB,
  FireWire) to connect the computer to external
  peripheral devices such as printers or scanners
• Some type of a removable media writer
• CD - the most common type of removable media,
  cheap but fragile.
• CD-ROM Drive
• CD Writer
• DVD
• DVD-ROM Drive
• DVD Writer
• DVD-RAM Drive
• Floppy disk
• Zip drive
• USB flash drive AKA a Pen Drive
• Tape drive - mainly for backup and long-term
  storage

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Personal Computer Hardware

• Internal storage - keeps data inside the computer
  for later use.
• Hard disk - for medium-term storage of data.
• Disk array controller
• Sound card - translates signals from the system
  board into analog voltage levels, and has
  terminals to plug in speakers.
• Networking - to connect the computer to the
  Internet and/or other computers
• Modem - for dial-up connections
• Network card - for DSL/Cable internet, and/or
  connecting to other computers.
• Other peripherals
• In addition, hardware can include external
  components of a computer system. The following
  are either standard or very common.
• Wheel Mouse

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Personal Computer Hardware

• Input or Input devices
• Text input devices
• Keyboard
• Pointing devices
• Mouse
• Trackball
• Gaming devices
• Joystick
• Gamepad
• Game controller
• Image, Video input devices
• Image scanner
• Webcam
• Audio input devices
• Microphone
• Output or Output devices
• Image, Video output devices
• Printer Peripheral device that produces a hard
  copy. (Inkjet, Laser)
• Monitor Device that takes signals and displays
  them. (CRT, LCD)

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Motherboard

• A typical computer is built with the
  microprocessor, main memory, and other basic
  components on the motherboard. Other components
  of the computer such as external storage, control
  circuits for video display and sound, and
  peripheral devices are typically attached to the
  motherboard via ribbon cables, other cables, and
  power connectors.
• A typical motherboard provides attachment points
  for one or more of the following CPU, graphics
  card, sound card, hard disk controller, memory
  (RAM), and external peripheral devices. The
  connectors for external peripherals are nearly
  always color coded according to the PC 99
  specification.

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Power Supply
Power supplies, often referred to as "switching
power supplies", use switcher technology to
convert the AC input to lower DC voltages. The
typical voltages supplied are 3.3 volts 5
volts 12 volts The 3.3- and 5-volts are
typically used by digital circuits, while the
12-volt is used to run motors in disk drives and
fans.
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Case
Cases usually come with room for a power supply
unit, several expansion slots and expansion bays,
wires for powering up a computer and some with
built in I/O ports that must be connected to a
motherboard. Motherboards are screwed to the
bottom or the side of the case, its I/O ports
being exposed on the back of the case. Usually
the power supply unit is at the top of the case
attached with several screws. The typical case
has four 5.25" and three 3.5" expansion bays for
devices such as hard drives, floppy disk drives
and CD-ROMs. A power button and sometimes a reset
button are usually located on the front. LED
status lights for power and hard drive activity
are often located near the power button and are
powered from wires that are connected with the
motherboard. Some cases come with status
monitoring equipment such as case temperature or
processor speed monitors.
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Disk Drive

• Capacity, usually quoted in gigabytes. (older
  hard disks used to quote their smaller capacities
  in megabytes)
• Physical size, usually quoted in inches
• Almost all hard disks today are of either
  the 3.5" or 2.5" varieties, used in desktops and
  laptops, respectively.

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CD ROM
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DVD ROM
DVD (commonly "Digital Versatile Disc" or
"Digital Video Disc") is an optical disc storage
media format that can be used for data storage,
including movies with high video and sound
quality. DVDs resemble compact discs as their
diameter is the same (120 mm (4.72 inches) or
occasionally 80 mm (3.15 inches) in diameter),
but they are encoded in a different format and at
a much higher density.
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Tape Drives

• Instead of allowing random-access to data as hard
  disk drives do, tape drives only allow for
  sequential-access of data. A hard disk drive can
  move its read/write heads to any random part of
  the disk platters in a very short amount of time,
  but a tape drive must spend a considerable amount
  of time winding tape between reels to read any
  one particular piece of data. As a result, tape
  drives have very slow average seek times. Despite
  the slow seek time, tapes drives can stream data
  to tape very quickly. For example, modern LTO
  drives can reach continuous data transfer rates
  of up to 80 MB/s, which is as fast as most 10,000
  rpm hard disks.

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Removable Disks

• The disk format itself had no more capacity than
  the more popular (and cheaper) 5¼-inch floppies.
  Each side of a double-density disk held 180 KB
  for a total of 360 KB per disk, and 720 KB for
  quad-density disks.13 Unlike 5¼-inch or 3½-inch
  disks, the 3-inch disks were designed to be
  reversible and sported two independent
  write-protect switches. It was also more reliable
  thanks to its hard casing.
• USB Flash Drives currently are sold from
  32 megabytes up to 64 gigabytes

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IDE Controller

• Built into the motherboard, two connections
  provide for ribbon cables that send signals
  controlling disk drives

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AGP Expansion Slots

• The Accelerated Graphics Port (also called
  Advanced Graphics Port) is a high-speed
  point-to-point channel for attaching a graphics
  card to a computer's motherboard, primarily to
  assist in the acceleration of 3D computer
  graphics. Some motherboards have been built with
  multiple independent AGP slots. AGP is currently
  being phased out in favor of PCI Express.

Superseded By PCI Express (2004)
Width 32 bits
Number of Devices 1 device/slot
Speed up to 2133 MB/s
Style Parallel
Hotplugging? no
External? no
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PCI Expansion Slot

• The Peripheral Component Interconnect, or PCI
  Standard (in practice almost always shortened to
  PCI) specifies a computer bus for attaching
  peripheral devices to a computer motherboard.
  These devices can take any one of the following
  forms
• An integrated circuit fitted onto the motherboard
  itself, called a planar device in the PCI
  specification.
• An expansion card that fits in sockets.

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Video Card

• A video card, (also referred to as a graphics
  accelerator card, display adapter and numerous
  other terms), is an item of personal computer
  hardware whose function is to generate and output
  images to a display. The term is usually used to
  refer to a separate, dedicated expansion card
  that is plugged into a slot on the computer's
  motherboard, as opposed to a graphics controller
  integrated into the motherboard chipset.

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Sound Card

• A sound card is a computer expansion card that
  can input and output sound under control of
  computer programs. Typical uses of sound cards
  include providing the audio component for
  multimedia applications such as music
  composition, editing video or audio,
  presentation/education, and entertainment
  (games). Many computers have sound capabilities
  built in, while others require these expansion
  cards if audio capability is desired.

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Random Access Memory (RAM)

• Random access memory (usually known by its
  acronym, RAM) is a type of data store used in
  computers. It takes the form of integrated
  circuits that allow the stored data to be
  accessed in any order that is, at random and
  without the physical movement of the storage
  medium or a physical reading head.
• The word "random" refers to the fact that any
  piece of data can be returned quickly, and in a
  constant time, regardless of its physical
  location and whether or not it is related to the
  previous piece of data. This contrasts with
  storage mechanisms such as tapes, magnetic disks
  and optical disks, which rely on the physical
  movement of the recording medium or a reading
  head. In these devices, the movement takes longer
  than the data transfer, and the retrieval time
  varies depending on the physical location of the
  next item.

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Clock

• In electronics and especially synchronous digital
  circuits, a clock signal is a signal used to
  coordinate the actions of two or more circuits.
• A clock signal oscillates between a high and a
  low state, normally with a 50 duty cycle, and is
  usually a square wave.
• Circuits using the clock signal for
  synchronization may become active at either the
  rising or falling edge, or both of the clock
  signal.
• Most integrated circuits (ICs) of sufficient
  complexity utilize a clock signal in order to
  synchronize different parts of the circuit and to
  account for propagation delays.
• As ICs become more complex, the problem of
  supplying accurate and synchronized clocks to all
  the circuits becomes increasingly difficult. The
  preeminent example of such complex chips is the
  microprocessor, the central component of modern
  computers.

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Basic Input/Output System

• BIOS, in computing, stands for Basic Input/Output
  System also incorrectly known as Basic Integrated
  Operating System. BIOS refers to the firmware
  code run by a computer when first powered on. The
  primary function of the BIOS is to prepare the
  machine so other software programs stored on
  various media (such as hard drives, floppies, and
  CDs) can load, execute, and assume control of the
  computer. This process is known as booting up.
• BIOS can also be said to be a coded program
  embedded on a chip that recognises and controls
  various devices that make up the computer. The
  term BIOS is specific to personal computer
  vendors. Among other classes of computers, the
  generic terms boot monitor, boot loader or boot
  ROM are commonly used.

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Microprocessor

• A microprocessor (sometimes abbreviated µP) is a
  programmable digital electronic component that
  incorporates the functions of a central
  processing unit (CPU) on a single semiconducting
  integrated circuit (IC). The microprocessor was
  born by reducing the word size of the CPU from 32
  bits to 4 bits, so that the transistors of its
  logic circuits would fit onto a single part. One
  or more microprocessors typically serve as the
  CPU in a computer system, embedded system, or
  handheld device.

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Heat Sink and Fan

• A heat sink is an environment or object that
  absorbs and dissipates heat from another object
  using thermal contact (in either direct or
  radiant contact).

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Universal Serial Bus (USB)

• Universal Serial Bus (USB) is a serial bus
  standard to interface devices. It was originally
  designed for computers, but its popularity has
  prompted it to also become commonplace on video
  game consoles, PDAs, portable DVD and media
  players, cellphones and even devices such as
  televisions, home stereo equipment (e.g., digital
  audio players), car stereos and portable memory
  devices.
• The radio spectrum based USB implementation is
  known as Wireless USB.

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Keyboard

• A computer keyboard is a peripheral partially
  modeled after the typewriter keyboard. Keyboards
  are designed for the input of text and characters
  and also to control the operation of a computer

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Network Connector

• An electrical connector is a device for joining
  electrical circuits together. The connection may
  be temporary, as for portable equipment, or may
  require a tool for assembly and removal, or may
  be a permanent electrical joint between two wires
  or devices. There are hundreds of types of
  electrical connectors. In computing, an
  electrical connector can also be known as a
  physical interface.

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Parallel Port

• A parallel port is a type of socket found on
  personal computers for interfacing with various
  peripherals. It is also known as a printer port
  or Centronics port. The IEEE 1284 standard
  defines the bi-directional version of the port.
• For the most part, the USB interface has replaced
  the Centronics-style parallel port as of 2006,
  most modern printers are connected through a USB
  connection, and often don't even have a parallel
  port connection. On many modern computers, the
  parallel port is omitted for cost savings, and is
  considered to be a legacy port. In laptops,
  access to a parallel port is still commonly
  available through docking stations.

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Serial Port

• In computing, a serial port is a serial
  communication physical interface through which
  information transfers in or out one bit at a time
  (contrast parallel port). Throughout most of the
  history of personal computers, data transfer
  through serial ports connected the computer to
  devices such as terminals or modems. Mice,
  keyboards, and other peripheral devices also
  connected in this way.
• While such interfaces as Ethernet, FireWire, and
  USB all send data as a serial stream, the term
  "serial port" usually identifies hardware more or
  less compliant to the RS-232 standard, intended
  to interface with a modem or with a similar
  communication device.
• For the most part, the USB interface has replaced
  the serial port as of 2006, most modern
  computers are connected to devices through a USB
  connection, and often don't even have a serial
  port connection. The serial port is omitted for
  cost savings, and is considered to be a legacy
  port.

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Modem

• A modem (from modulate and demodulate) is a
  device that modulates an analog carrier signal to
  encode digital information, and also demodulates
  such a carrier signal to decode the transmitted
  information. The goal is to produce a signal that
  can be transmitted easily and decoded to
  reproduce the original digital data.
• Faster modems are used by Internet users every
  day, notably cable modems and ADSL modems.

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Operating System

• An operating system (OS) is a computer program
  that manages the hardware and software resources
  of a computer. At the foundation of all system
  software, the OS performs basic tasks such as
  controlling and allocating memory, prioritizing
  system requests, controlling input and output
  devices, facilitating networking, and managing
  files. It also may provide a graphical user
  interface for higher level functions. It forms a
  platform for other software.
• Services
• Process Management
• Disk and File Management
• Internal/External Security
• Networking
• Graphical User Interfaces (GUI)
• Device Drivers

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Microsoft Windows OS

• The Microsoft Windows family of operating systems
  originated as a graphical layer on top of the
  older MS-DOS environment for the IBM PC. Modern
  versions are based on the newer Windows NT core
  that first took shape in OS/2 and borrowed from
  VMS. Windows runs on 32-bit and 64-bit Intel and
  AMD processors, although earlier versions also
  ran on the DEC Alpha, MIPS, Fairchild (later
  Intergraph) Clipper and PowerPC architectures
  (some work was done to port it to the SPARC
  architecture).
• As of 2006, Windows held a near-monopoly of
  around 94 of the worldwide desktop market share,
  although some predict this to dwindle due to the
  increased interest in open source operating
  systems.1 It is also used on low-end and
  mid-range servers, supporting applications such
  as web servers and database servers. In recent
  years, Microsoft has spent significant marketing
  and RD money to demonstrate that Windows is
  capable of running any enterprise application
  which has resulted in consistent
  price/performance records (see the TPC) and
  significant acceptance in the enterprise market
  at the cost of existing Unix based system market
  share.

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Other Operating Systems

• Macintosh Operating System
• Apple deliberately downplayed the existence of
  the operating system in the early years of the
  Macintosh to help make the machine appear more
  user-friendly and to distance it from other
  operating systems such as MS-DOS, which were
  portrayed as arcane and technically challenging.
  Apple wanted Macintosh to be portrayed as a
  computer "for the rest of us". The term "Mac OS"
  did not really exist until it was officially used
  during the mid-1990s. The term has since been
  applied to all versions of the Mac system
  software as a handy way to refer to it when
  discussing it in context with other operating
  systems.
• Unix/Linix
• Unix systems run on a wide variety of machine
  architectures. They are used heavily as server
  systems in business, as well as workstations in
  academic and engineering environments. Free
  software Unix variants, such as Linux and BSD,
  are popular but have not reached significant
  market share in the desktop market. They are used
  in the desktop market as well, for example
  Ubuntu, but mostly by hobbyists.

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How a Disk Boot Wakes Up a PC

• A personal computer can't do anything useful
  unless it's running an operating system
• A basic type of software, such as Microsoft
  Windows, that acts as a supervisor for all the
  applications, games, or other programs you use.
• The operating system sets the rules for using
  memory, drives, and other parts of the computer.
• Before a PC can run an operating system, it needs
  some way to load the operating system from disk
  to random access memory (RAM).
• The way to do this is with the bootstrap, or
  simply to boota small amount of code that's a
  permanent part of the PC.

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Power On Self Test

• Turn on your PC, electricity warms up the
  components that send, receive, and memorize bits
  and bytes of data rushing through the system. One
  stream of electricity follows the same
  permanently programmed path it has followed each
  time the computer came to life.
• The path takes current to the CPU, or
  microprocessor. The electrical signal clears
  leftover data from the chip's internal memory
  registers and places a specific hexadecimal
  number, F000, into one of the CPU's digital note
  pads, called the program counter.
• Whatever number is in the program counter tells
  the CPU the memory address of the next
  instruction. In this case, it's the first
  instruction, located on a flash memory chip on
  the computer's motherboard. This chip holds a few
  small programsthat determine how your computer
  works. All together, they're called the BIOS.
• Now the BIOS awakens the computer's components,
  performing the power-on self-test (POST) to make
  sure the computer is functioning properly.

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Boot

• BIOS checks a small, 64-byte chuck of RAM that is
  kept alive by a battery even when the computer is
  off that contains the official record of which
  components are installed in your system.
• The BIOS and CPU check to make sure they're
  working right.
• The BIOS loads device drivers and interrupt
  handlers into memory the for the basic hardware
  in the system, such as the keyboard, mouse, hard
  drive, and floppy drive.
• To be sure all the PC's operations function in a
  synchronized, orderly fashion, the CPU also
  checks the system's clock, which is responsible
  for pacing signals.
• The CPU sends signals over the system bus to be
  sure all of the components are functioning.
• The POST tests the memory contained on the
  display adapter and the video signals that
  control the display. At this point, you'll first
  see something appear on your PC's monitor.
• The BIOS checks to see if it's engaged in a cold
  boot, meaning the computer had been turned off,
  or if it's a warm boot, or reboot, by checking
  the value at memory address 00000472.
• For a cold boot the BIOS runs a series of tests
  to ensure that the RAM chips are functioning
  properly.
• The tests write data to each chip, and then read
  it and compare what they read with the data sent
• The POST sends signals over specific paths on the
  bus to the internal floppy, optical, and hard
  disk drives, and listens for a response to
  determine which drives are available.

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After the POST

• A typical Windows XP boot sequence starts with
  the MBR loading the bootstrap loader for the OS,
  which will tell the computer everything it needs
  to know about its memory and how to use it, how
  the files are stored, and put up the boot menu.
• In many computers, the boot menu is not shown
  unless the user asks for it. The bootloader then
  launches a program that collects more information
  about the hardware installed in it and then loads
  the core operating system files.
• Then, it reads the registry from which it gathers
  the information necessary to communicate with
  different components, and then load the necessary
  programs (drivers) to communicate with devices
  attached to the computer.

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After the POST

• Once this is done, the bootloader loads the
  program that shows the welcome or logon screen.
  Once the user logs in, the computer loads the
  shell (Explorer), which shows the desktop to the
  user. At this point, the OS is loaded and the
  computer is ready for use.
• A typical boot takes about a minute, with the
  BIOS boot sequence taking about 10-15 seconds.
• The term booting is short for bootstrapping. The
  word bootstrapping is derived from the phrase
  "pulling himself up by his bootstraps", which has
  its origins in the tall stories narrated by Baron
  Munchhausen, a German nobleman in the eighteenth
  century.

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How an Operating System Controls PC Hardware

• OPERATING systems originally were developed to
  handle one of the most complex input/output
  operations communicating with a variety of disk
  drives. This is evidenced by the names given to
  early operating systems, which often contained
  the acronym DOS, for disk operating system.
  Eventually, the operating system quickly evolved
  into an all-encompassing bridge between your PC
  and the software you run on it.

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41
How Hardware and Software Work Together

• Choose a command, like save
• Word processor tells OS to save
• OS knows how to control hardware
• OS does infrastructure work
• Program does your work

42
How Hardware and Software Work Together

• Device Drivers
• A device driver, or a software driver is a
  specific type of computer software, typically
  developed to allow interaction with hardware
  devices.
• This usually constitutes an interface for
  communicating with the device, through the
  specific computer bus or communications subsystem
  that the hardware is connected to,
• Driver provides commands to and receives data
  from the device, and on the other end, the
  requisite interfaces to the operating system and
  software applications.
• Often called simply a driver, it is a specialized
  hardware-dependent computer program, which is
  operating system specific, that enables another
  program, typically an operating system or
  applications software package, to interact
  transparently with the given device.
• Usually provides the requisite interrupt handling
  required for any necessary asynchronous
  time-dependent hardware interfacing needs.

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Types of Hardware Drivers

• Because of the diversity of modern hardware and
  operating systems, many ways exist in which
  drivers can be used. Drivers are used for
  interfacing with
• Printers
• Video adapters
• Network cards
• Sound cards
• Local buses of various sorts - in particular, for
  bus mastering on modern systems
• Low-bandwidth I/O buses of various sorts (for
  pointing devices such as mice, keyboards, USB,
  etc.)
• computer storage devices such as hard disk,
  CD-ROM and floppy disk buses (ATA, SATA, SCSI)
• Implementing support for different file systems
• Implementing support for image scanners and
  digital cameras

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Enhanced Integrated Drive Electronics (EIDE)

• A disk drive device driver
• An enhanced version of the IDE drive interface
• Expands the maximum disk size from 504 MB to 8.4
  GB,
• More than doubles the maximum data transfer rate,
  
• And supports up to four drives per PC (as opposed
  to two in IDE systems).
• Now that hard disks with capacities of 1 GB or
  more are commonplace in PCs,
• EIDE is an extremely popular interface.
• EIDE's primary competitor is SCSI-2, which also
  supports large hard disks and high transfer
  rates.

45
Enabling Disk Access

• Disk controller translates instructions from the
  BIOS and Disk Drivers into electrical signals
• Move drives read/write head to proper location
• Create or read magnetic signals that represent
  data

46
HW Interrupts

1. Press a key, an electrical signal identifies what
   key you pressed, to the keyboard controller.
2. The keyboard interrupt arrives on one of 16
   interrupt request (IRQ) lines. Seven of the IRQs
   monitor specific components, such as the keyboard
   controller.
3. The controller relays a signal to the interrupt
   controller that determines which of the 256
   possible kinds of interrupts request the CPU's
   attention.
4. More than one expansion card on the PCI
   Peripheral Component Interconnect (PCI) and
   PCI-Express slots can use the same IRQ because
   the requests are managed by the Plug 'n' Play
   function.
5. The interrupt controller sends a signal called
   the INTR, used for normal interrupt signals.
6. The CPU puts whatever it was doing on hold.
7. A CPU uses one of two methods from computing
   polling and interrupts.
8. The CPU checks to find out what key you pressed.
   The CPU checks a section of memory called the
   interrupt descriptor table (IDT). Specifically,
   the CPU performs the instructions at one of the
   IDT's locations associated with the key.
9. When the interrupt software completes its job, it
   sends an instruction to the CPU. That tells the
   CPU it is free to return to whatever it was doing
   before it was interrupted.

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How Plug and Plan Works

• With Plug and Play under Microsoft
  Windows Server 2003, you can connect a hardware
  device to your system and leave the job of
  configuring and starting the device to the
  operating system. If the device and drivers are
  not designed to take advantage of Plug and Play,
  Windows Server 2003 will not be able to
  automatically configure and start the device.
  Plug and Play in Windows Server 2003 supports a
  wide range of devices.
• In Windows Server 2003, Plug and Play support is
  optimized for computers that include an Advanced
  Configuration and Power Interface (ACPI) BIOS.
  ACPI devices are defined by the Advanced
  Configuration and Power Interface (ACPI)
  Specification, a hardware and software interface
  specification that combines and enhances the Plug
  and Play and Advanced Power Management (APM)
  standards. ACPI devices include low-level system
  devices such as batteries and thermal zones.
• Plug and Play detection runs with the logon
  process and relies on system firmware, hardware,
  device drivers, and operating system features to
  detect and enumerate new devices. ACPI firmware
  provides enhanced features, such as hardware
  resource sharing. When Plug and Play components
  are coordinated, Windows Server 2003 can detect
  new devices, allocate system resources, and
  install or request drivers with minimal user
  intervention.

48
Plug and Play Architecture
49
Plug and Plan Driver Installation
When a hardware device is connected as when you
plug a USB camera into a USB port Plug and Play
Manager goes through the following steps to
install the device.

• When a hardware device is connected as when you
  plug a USB camera into a USB port Plug and Play
  Manager goes through the following steps to
  install the device.
• After receiving an insertion interrupt, Plug and
  Play Manager checks what hardware resources the
  device needs
• memory ranges, I/O ranges, and DMA channels. Plug
  and Play Manager then assigns those resources.
• Plug and Play Manager checks the hardware
  identification number of the device.
• Plug and Play Manager then checks the hard drive,
  floppy drives, CD-ROM drives, and Windows Update
  for drivers that match the number of the device.
• If multiple drivers are found, Plug and Play
  Manager chooses the driver that is the best match
  by looking for the closest hardware ID or
  compatible ID match, driver signatures, and other
  driver features.
• Plug and Play Manager then installs the
  best-match driver and the operating system starts
  the device.

50
Homework

• Prepare a single page paper addressing each of
  the following questions
• What is the registry?
• What does it do?
• How does it work?
• Why does a PC require a registry?

Due Next Week