1. How Hardware and Software Work Together
Chapter 2
How Hardware and Software Work Together

2. You Will Learn… How hardware and software interact
How system resources help hardware and 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

3. Hardware and Software Interaction: An Overview
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

4. Hardware and Software Interaction

5. 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
Does not relate directly with hardware; uses BIOS or device drivers for the interface

7. Categories of PC Software
BIOS (basic input/output system) and device drivers
Operating system (OS)
Application software

8. Categories of BIOS (Firmware) Programs
System BIOS
To control I/O devices
Startup BIOS
To control startup of computer
CMOS setup
To change setup information

9. Device Drivers
Small programs stored on hard drive that tell computer how to communicate with an I/O device
Necessary for communication between OS and more complex devices

10. Operating System (OS)
Works with system BIOS and device drivers to provide instructions to hardware to perform tasks

11. 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

12. System Resources

13. 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
Each line on a bus can perform several functions (multiplexing)

16. 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

17. Common Uses for Some IRQs

18. 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)

19. IRQs

20. Use Device Manager to See How IRQs Are Assigned

21. Use Device Manager to See How IRQs Are Assigned

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

23. How Memory Addresses Are Assigned
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

24. Division of Memory

25. Shadowing ROM
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
Also called shadow RAM

26. I/O Addresses
Numbers the CPU can use to access hardware devices, in much the same way it uses memory addresses to access physical memory
Also called port addresses or ports

27. I/O Addresses

29. DMA Channels
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:
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

30. DMA Channels

31. 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

32. Plug and Play (PnP) Standard
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
Applies to OS, BIOS on the motherboard, and BIOS on devices

33. Functions Performed During 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
continued…

34. Functions Performed During 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

35. 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

36. Steps in the Boot Process
Step 1: POST
Step 2: ROM BIOS startup program searches 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

37. Boot Step 1: POST

38. Boot Step 2: How BIOS Finds/Loads the OS

40. Boot Step 3: Loading the MS-DOS Core of Windows 9x

41. Autoexec.bat Stands for automatically executed batch program
Lists OS commands that are executed automatically each time OS is loaded

42. Typical Commands in Autoexec.bat File
Path command (eg, PATH C:\;C:\PCTOOLS;)
Directs OS to look in two different directories for program files
Restart command (Restart.com)
Causes system to reboot
continued…

43. Typical Commands in Autoexec.bat File
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)

44. 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