1. How Hardware and Software Work Together Chapter 2

2. Chapter Objectives • How an operating system manages hardware. • How system resources help hardware and software communicate. • The steps involved in booting your computer.

3. How an OS Manages Hardware • Operating System – software that controls the computer. • Manages hardware • Runs applications • Provides an interface for users • Stores, retrieves and manipulates files • The OS is the middle man between software and hardware.

4. How an OS Manages Hardware • Most common OS today are Windows XP, Windows 2000, and Windows 98/ME. • Mac OS and Linux are two OS not made by Microsoft. • Since the OS does relate directly to hardware, it needs drivers or BIOS to interface with the hardware. • Figure 2-2 pg. 41

5. How an OS Manages Hardware • Most PC software falls into 3 categories. • Device drivers or the BIOS • Operating System • Application software

6. How an OS Manages Hardware • Device drivers – small programs stored on the hard drive that tell the computer how to communicate with a specific hardware device. • Problem: see if you can locate the drivers for an HP 955c Deskjet printer (go to www.hp.com) • Basic input/output is hard coded directly on the BIOS chip.

7. How an OS Manages Hardware • ROM BIOS programs fall into 3 categories: • Programs to control I/O devices, called system BIOS. • Programs to control the startup of a computer, called startup BIOS. • Programs to change the setup information stored in CMOS, called CMOS setup,

8. How an OS Uses Device Drivers • Used to interface with specific hardware. • Stored on the hard drive. • Some device drivers are installed when the OS is first installed or when new hardware is added to a system. • Hardware such as printers, scanners, and digital cameras need device drivers in order to work. • Usually these drivers are installed before the component is connected.

9. How an OS Uses Device Drivers • Before installing a new hardware device on Windows 2000/XP systems, always check the hardware compatibility list (HCL) to determine if the driver will work under that OS. • http://www.microsoft.com/whdc/hcl/default.mspx

10. How an OS Uses System BIOS to Manage Devices • The OS communicates with simple devices, such as Floppy drives or keyboards through system BIOS. • System BIOS are also used to access the computers hard drive. • If the OS has the choice, it will choose to use device drivers instead of system BIOS.

11. How an OS Uses System BIOS to Manage Devices • Recall, system BIOS are stored in ROM. • Because RAM is accessed faster than ROM, system BIOS might be copied into RAM. • Called Shadow ROM or Shadow RAM.

12. System Resources • System Resource – a tool used by either hardware or software to communicate with the other. • When BIOS or a driver wants to send data to a device, or when the device needs attention, the device or software uses system resources to communicate.

13. System Resources • 4 types of system resources: • Memory addresses • I/O addresses • IRQ (Interrupt request numbers) • Direct memory address (DMA) channels. • Table 2-1 pg. 46

14. System Resources

15. System Resources • Hardware devices signal the CPU for attention by using IRQ. • Software addresses a device by using one of its I/O addresses. • Software looks at memory as a hardware device and addresses it with memory addresses. • DMA channels pass data back and forth between a hardware device and memory.

16. System Resources • Figure 2-7 • All four system resources depend on certain lines on a bus on the motherboard. • A bus system has 3 components: • Data bus carries the data • Address bus communicates addresses (both memory address and I/O addresses) • Control bus controls communication (IRQ’s and DMA channels)

17. IRQ • When the keyboard needs the CPU to process a keystroke after a key has been pressed, the device needs a way to get the CPU’s attention, and the CPU must know what to do once its attention is turned to the device.

19. IRQ • These interruptions to the CPU are called Hardware Interrupts. • The device initiates an interrupt by placing voltage on the designated IRQ line assigned to it. • This voltage on the line serves as a signal to the CPU. • Table 2-2 pg. 47 - 48

20. IRQ • On motherboards, part of the chip set called the interrupt controller manage the IRQs for the CPU. • If more than 1 IRQ is up at the same time, the IRQ with the lower value will be processed first. • Figure 2-8 pg. 49 • Figure 2-9 pg. 50 • Figure 2-10 pg. 51

21. IRQ • Polling – software that is constantly running has the CPU periodically check the hardware device to see if it needs service.

22. Memory Addresses • An OS relates to memory as a long list of cells that it can use to hold data and instructions. • Similar to a one dimensional spreadsheet. • Each cell, memory location, is assigned a number beginning with 0. • These numbers are assigned when the OS is loaded and are called Memory Addresses.

23. Memory Addresses • Figure 2-11 pg. 52 • Think of memory addresses as a seat number in a theater. • Each seat is assigned a number regardless of whether someone is sitting in the seat. • The person sitting in the seat can be the data. • The OS does not refer to the person by name, but only by seat number.

24. Input/Output Address • I/O addresses, or port addresses, are numbers the CPU can addresses to access physical memory. • Figure 2-12 pg. 53 • Basically, the CPU knows the hardware device as a group of I/O addresses.

25. DMA Channels • DMA – Direct memory access • Shortcut method that lets an I/O device to send data directly to memory bypassing the CPU. • Chip on the motherboard that contains the instructions and logic of DMA. • Figure 2-13 pg. 54

26. OS Tools to Examine a System • Device Manager • Allows you to manage hardware devices. • System Information Utility • Gives information similar to that given by the Device Manager. • Microsoft Diagnostic Utility • Used to view information about the system, including information about memory, video, ports, device drivers, and system resources.

27. Booting Up Your Computer • Booting – the computers ability to bring itself to an operable state without user intervention. • Soft boot – turning the system on by using the OS. • Usually a fast boot process. • Hard boot – turning the computer on with an on/off switch. • More stressful on the machine.

28. Booting Up Your Computer • If you have the choice, always perform a soft boot. • If you have to perform a hard boot, wait a few seconds before you turn the computer back on.

29. Startup BIOS Controls the Beginning of the Boot • Step 1: Startup BIOS runs the power on self test (POST) and assigns resources. • Step 2: The ROM BIOS startup program searches for and loads the OS. • Step 3: The OS configures the system and completes its own loading. • Step 4: Application software is loaded and executed.

30. POST and Assignment of System Resources • Steps Used In POST • When the power is first turned on, the system clock begins to generate clock pulses. • The CPU begins working and initializes itself. • The CPU turns to memory address FFFF0h, which is the memory address always assigned to the first instruction in the ROM BIOS to run POST. • This instruction directs the CPU to run the POST test. • POST first checks the BIOS program operating it, and then tests CMOS RAM.

31. POST and Assignment of System Resources • A test determines that there has not been a battery failure. • Hardware interrupts are disabled. • Tests are run on the CPU. • A check determines if this is a cold boot, and hardware is inventoried. • Hardware devices are tested and configured. • Some devices are sent to Sleep Mode to save electricity. • CMOS setup is ran if requested. • BIOS begins its search for an OS.