Transcript Hardware and Software Interaction

Chapter 2
How Hardware and
Software Work
Together
You Will Learn…
• How hardware and software interact
• How system resources help hardware and
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software communicate
How BIOS and device drivers are used to send
instructions to hardware
How different operating systems work
The steps involved in booting your computer
Hardware and Software Interaction:
An Overview
• Software
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Intelligence of the computer
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Determines what hardware is present
• Decides how hardware is configured and used
• Uses hardware to perform tasks
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Consists of programs that instruct computers to
perform specific tasks
Hardware and Software Interaction
Operating System (OS)
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Software that controls a computer
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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
Categories of PC Software
• BIOS (basic input/output system) and device
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drivers
Operating system (OS)
Application software
Categories of BIOS (Firmware)
Programs
• System BIOS
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To control I/O devices
• Startup BIOS
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To control startup of computer
• CMOS setup
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To change setup information
Device Drivers
• Small programs stored on hard drive that tell
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computer how to communicate with an I/O
device
Necessary for communication between OS and
more complex devices
Operating System (OS)
• Works with system BIOS and device drivers to
provide instructions to hardware to perform
tasks
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
System Resources
The 8-bit and 16-bit ISA Slots
• 8-bit ISA bus had a limited number of system
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resources available to it
Number was increased with invention of 16-bit
ISA bus
Each line on a bus can perform several
functions (multiplexing)
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
Common Uses for Some IRQs
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)
IRQs
Use Device Manager to See How
IRQs Are Assigned
Use Device Manager to See How
IRQs Are Assigned
Memory Addresses
• Hexadecimal numbers, often written in
segment/offset form, assigned to RAM and
ROM so that the CPU can access both
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
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
Number of memory addresses partly depends on size
of memory bus
Division of Memory
Shadowing ROM
• Process of copying programs from ROM to
RAM for execution
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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
• Also called shadow RAM
I/O Addresses
• Numbers the CPU can use to access hardware
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devices, in much the same way it uses memory
addresses to access physical memory
Also called port addresses or ports
I/O Addresses
DMA Channels
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Provide shortcut method so an I/O device can send
data directly to memory, bypassing the CPU
A chip on the motherboard contains DMA logic and
manages the process
Each channel requires two lines to manage it:
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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
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)
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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)
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Uses OS to reboot
Faster than hard boot
Plug and Play (PnP) Standard
• Simplifies installation of hardware devices
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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
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
continued…
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
Startup BIOS Controls the
Beginning of the Boot
• Startup BIOS is in control for first three steps
and beginning of the fourth, where control is
turned over to the OS
Steps in the Boot Process
• Step 1: POST
• Step 2: ROM BIOS startup program searches
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for and loads an OS (most often from logical
drive C on the hard drive)
Step 3: OS configures the system and
completes its own loading
Step 4: User executes application software
Boot Step 1: POST
Boot Step 2: How BIOS Finds/Loads
the OS
Boot Step 3: Loading the
MS-DOS Core of Windows 9x
Autoexec.bat
• Stands for automatically executed batch
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program
Lists OS commands that are executed
automatically each time OS is loaded
Typical Commands in Autoexec.bat
File
• Path command (eg, PATH C:\;C:\PCTOOLS;)
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Directs OS to look in two different directories for
program files
• Restart command (Restart.com)
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Causes system to reboot
continued…
Typical Commands in Autoexec.bat
File
• Set command
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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)
Chapter Summary
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How hardware and software work together
What happens when a PC is turned on OS is loaded
System resources
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Interrupt request number (IRQ)
 Memory addresses
 I/O addresses
 DMA channels
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Booting up the computer