How Hardware and Software Work Together

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Chapter 2

• How Hardware and Software Work Together

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You Will Learn

• How hardware and software interact
• How BIOS and device drivers are used to send
  instructions to hardware
• How different operating systems work
• The steps involved in booting your computer

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Hardware and Software Interaction An Overview

• Software
• Intelligence of the computer
• Determines what hardware is present
• Decides how hardware is configured and used
• Uses hardware to perform tasks
• Consists of programs that instruct computers to
  perform specific tasks

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Operating System (OS)

• Software that controls a computer
• Manages hardware
• Runs applications
• Provides user interface
• Stores, retrieves, and manipulates files
• Communicates with hardware using system
  resources uses BIOS or device drivers for
  interface to system resources

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Categories of PC Software

• BIOS (basic input/output system) and device
  drivers
• Operating system (OS)
• Application software

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BIOS and Device Drivers

• Categories of BIOS (firmware) programs
• System BIOS
• Startup BIOS
• CMOS setup
• Device drivers
• Small programs stored on hard drive that tell
  computer how to communicate with an input/output
  device
• Necessary for communication between OS and more
  complex devices

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Operating System (OS)

• Works with system BIOS and device drivers to
  provide instructions to hardware to perform tasks

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System Resources

• Tools used by hardware or software to communicate
  with the other
• Memory addresses
• I/O addresses
• Interrupt request numbers (IRQs)
• Direct memory access (DMA) channels
• All four types depend on certain lines on a bus
  on the motherboard

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System Resources
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The 8-bit and 16-bit ISA Slots

• 8-bit ISA bus had a limited number of system
  resources available to it
• Number was increased with invention of 16-bit ISA
  bus

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Interrupt Request Number (IRQ)

• Line on a bus that a device uses to alert the CPU
  that it needs servicing
• Interruptions to CPU are called hardware
  interrupts
• Polling is an alternative to an interrupt

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Common Uses for Some IRQs
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IRQs

• Preconfigured assignments make it easier to
  configure devices and avoid conflicts with other
  devices
• COM1 and COM2 (for serial devices such as modems)
• LPT1 and LPT2 (for parallel devices such as
  printers)

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IRQs
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Memory Addresses

• Hexadecimal numbers, often written in
  segment/offset form, assigned to RAM and ROM so
  that the CPU can access both

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How Memory AddressesAre Assigned

• CPU has fixed number of memory addresses,
  determined by CPU and bus it is using
• They can be assigned to any type of physical
  memory in the system that needs to be addressed
  by the CPU
• Once addresses have been assigned (usually during
  boot process), CPU sees physical memory as a
  single list that can be accessed using memory
  addresses

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How Memory AddressesAre Assigned
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Shadowing ROM

• Process of copying programs from ROM to RAM for
  execution

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I/O Addresses

• Numbers the CPU can use to access hardware
  devices, in same way it uses memory addresses to
  access physical memory
• Also called port addresses or ports

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Assignments for I/O Addresses
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DMA Channels

• Provide shortcuts for a device to send data
  directly to memory bypasses CPU
• A chip on the motherboard contains DMA logic and
  manages the process
• Each channel requires two lines to manage it
• One for DMA controller to request clearance from
  CPU
• One used by CPU to acknowledge that DMA
  controller is free to send data over data lines
  without interference from CPU

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DMA Channels
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Booting up Your Computer

• Refers to the computer bringing itself up to an
  operable state without user intervention
• Hard boot (cold boot)
• Involves initially turning on power with on/off
  switch
• More stressful than soft boot because of initial
  power surge through equipment
• Soft boot (warm boot)
• Uses OS to reboot
• Faster than hard boot

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Plug and Play (PnP) Standard

• Makes installing hardware devices less
  complicated
• Rather than having to reset DIP switches and
  jumpers, OS and/or startup BIOS automatically
  configures hardware devices to reduce or
  eliminate conflicting requests for system
  resources
• Applies to OS, BIOS on the motherboard, and BIOS
  on devices

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Functions PerformedDuring the Boot

• Startup BIOS tests essential hardware components
  (power-on self test or POST)
• Setup information is used to configure both
  hardware and software
• Hardware components are assigned system resources
  they will later use for communication

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Functions PerformedDuring the Boot

• Startup BIOS finds the OS, which is loaded,
  configured, and executed
• Hardware devices are matched up with the BIOS and
  device drivers that control them
• Some application software may be loaded and
  executed

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Startup BIOS Controls the Beginning of the Boot

• Startup BOS is in control for first three steps
  and beginning of the fourth, where control is
  turned over to the OS

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Parts of the Boot Process

• Step 1 POST
• Step 2 ROM BIOS startup program searches for and
  loads an OS
• Step 3 OS configures the system and completes
  its own loading
• Step 4 User executes application software

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Boot Step 1
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How BIOS Finds/Loads the OS
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Boot Step 3
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Chapter Summary

• How hardware and software work together
• What happens when a PC is turned on OS is loaded
• System resources
• Interrupt request number (IRQ)
• Memory addresses
• I/O addresses
• DMA channels
• Booting up the computer, including when hard
  drive has failed