Chapter 1. How Hardware and Software Work Together

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Chapter 1 How Hardware and

Software Work

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You Will Learn…

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How hardware and software interact

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How system resources help hardware and software communicate

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How BIOS and device drivers are used to send instructions to hardware

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How different operating systems work

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Hardware and Software Interaction:

An Overview

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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}

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Operating System (OS)

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Software that controls a computer

 Manages hardware

 Runs applications

 Provides user interface

 Stores, retrieves, and manipulates files

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Communicates with hardware using system resources

 Does not relate directly with hardware; uses BIOS or device drivers for the interface

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Categories of PC Software

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BIOS (basic input/output system) and device drivers

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Operating system (OS)

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Categories of BIOS (Firmware)

Programs

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System BIOS

 _{To control I/O devices}

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Startup BIOS

 _{To control startup of computer}

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CMOS setup

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Device Drivers

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Small programs stored on hard drive that tell computer how to communicate with an I/O device

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Necessary for communication between OS and more complex devices

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Operating System (OS)

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

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System Resources

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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

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All four types depend on certain lines on a bus on the motherboard

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The 8-bit and 16-bit ISA Slots

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8-bit ISA bus had a limited number of system resources available to it

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Number was increased with invention of 16-bit ISA bus

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Each line on a bus can perform several functions (multiplexing)

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Interrupt Request Number (IRQ)

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Line on a bus that a device uses to alert the CPU that it needs servicing

 _{Interruptions to CPU are called hardware interrupts}

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IRQs

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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}

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Use Device Manager to See How

IRQs Are Assigned

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Use Device Manager to See How

IRQs Are Assigned

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Memory Addresses

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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 Addresses

Are Assigned

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CPU has fixed number of memory addresses, determined by CPU and the bus it is using

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They can be assigned to any type of physical memory in the system that needs to be addressed by the CPU

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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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Number of memory addresses partly depends on size of memory bus

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Shadowing ROM

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Process of copying programs from ROM to RAM for execution

 _{If ROM programs are executed directly from ROM}

chips, memory addresses are assigned to this ROM

 _{If programs are first copied to RAM, and then}

executed, the same memory addresses are assigned to this area of RAM

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I/O Addresses

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Numbers the CPU can use to access hardware devices, in much the same way it uses memory addresses to access physical memory

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DMA Channels

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Provide shortcut method so an I/O device can send data directly to memory, bypassing the CPU

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A chip on the motherboard contains DMA logic and manages the process

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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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Booting up Your Computer

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Refers to the computer bringing itself up to an operable state without user intervention

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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

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Soft boot (warm boot)

 Uses OS to reboot

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Plug and Play (PnP) Standard

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Simplifies installation of hardware devices

 _{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

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Applies to OS, BIOS on the motherboard, and BIOS on devices

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Functions Performed

During the Boot

1. Startup BIOS tests essential hardware

components (power-on self test or POST)

2. Setup information is used to configure both hardware and software

3. Hardware components are assigned system resources they will later use for

communication

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Functions Performed

During the Boot

4. Startup BIOS finds the OS, which is loaded, configured, and executed

5. Hardware devices are matched up with the BIOS and device drivers that control them

6. Some application software may be loaded and executed

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Startup BIOS Controls the

Beginning of the Boot

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

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Steps in the Boot Process

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Step 1: POST

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Step 2: ROM BIOS startup program searches for and loads an OS (most often from logical drive C on the hard drive)

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Step 3: OS configures the system and completes its own loading

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Boot Step 2: How BIOS Finds/Loads

the OS

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Boot Step 3: Loading the

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Autoexec.bat

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Stands for automatically executed batch program

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Lists OS commands that are executed automatically each time OS is loaded

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Typical Commands in Autoexec.bat

File

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Path command (eg, PATH C:\;C:\PCTOOLS;)

 _{Directs OS to look in two different directories for}

program files

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Restart command (Restart.com)

 _{Causes system to reboot}

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Typical Commands in Autoexec.bat

File

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Set command

 _{Appends a path to Path command without editing}

existing Path command line itself

(eg, SET PATH=%PATH%;C:\VERT)

 Creates and assigns a value to an environmental variable that can later be read by an application (eg, SET MYPATH=C:\VERT)

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Chapter Summary

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How hardware and software work together

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What happens when a PC is turned on OS is loaded

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System resources

 Interrupt request number (IRQ)

 Memory addresses

 I/O addresses

 DMA channels