Page 379 - DCAP103_Principle of operating system

Principles of Operating Systems

Notes Objectives

After studying this unit, you will be able to:
• Discuss input/output of Windows

• Explain Windows 2000 file system

• Explain security in Windows 2000

• Understand caching in Windows 2000
Introduction

A large part of the I/O manager’s role is the management of communication between drivers.
All drivers supply a standard set of services that the I/O manager can call. This uniform
interface allows the I/O manager to communicate with all drivers in the same way, without
any knowledge of how the devices they control actually work.

Drivers communicate with each other using data structures called I/O request packets. The
drivers do not pass I/O request packets to each other directly. Instead, they pass the packets to
the I/O manager, which delivers them to the appropriate destination drivers using the drivers’
standard services. The packets passed at the various stages are different—it’s a primary job of
each layer to construct the appropriate request packets to pass to the next layer.

13.1 Input/Output in Windows 2000

The goal of the Windows 2000 I/O system is to provide a framework for efficiently handling a
very wide variety of I/O devices. Current input devices include various kinds of keyboards, mice,
touch pads, joysticks, scanners, still cameras, television cameras, bar code readers, microphones,
and laboratory rats. Current output devices include monitors, printers, plotters, beamers, CD-
recorders, and sound cards. Storage devices include floppy disks, IDE and SCSI hard disks,
CD-ROMs, DVDs, Zip drives, and tape drives. Finally, other devices include clocks, networks,
telephones, and camcorders. No doubt many new I/O devices will be invented in the years to
come, so Windows 2000 has been designed with a general framework to which new devices can
easily be attached. In the following sections we will examine some of the issues relating to I/O.

13.1.1 Fundamental Concepts of Input/Output in Windows 2000

The I/O manager is on intimate terms with the plug-and-play manager. The basic idea behind
plug and play is that of an enumerable bus. Many buses, including PC Card, PCI, USB, IEEE
1394, and SCSI, have been designed so that the plug-and-play manager can send a request to
each slot and ask the device there to identify itself. Having discovered that what is out there,
the plug-and-play manager allocates hardware resources, such as interrupt levels, locates the
appropriate drivers, and loads them into memory. As each one is loaded, a driver object is
created for it. For some buses, such as SCSI, enumeration happens only at boot time, but for
other buses, such as USB and IEEE 1394, it can happen at any moment, requiring close contact
between the plug-and-play manager, the bus driver (which actually does the enumeration),
and the I/O manager.

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