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Unformatted text preview: P ART F IVE P erhaps the messiest parts of the design of an operating system deal with the I/O facility and the file management system.With respect to I/O, the key issue is performance. The I/O facility is truly the performance battleground. Look- ing at the internal operation of a computer system, we see that processor speed con- tinues to increase and,if a single processor is still not fast enough,SMP configurations provide multiple processors to speed the work. Internal memory access speeds are also increasing, though not at as fast a rate as processor speed. Nevertheless, with the clever use of one, two, or even more levels of internal cache, main memory access time is managing to keep up with processor speed. But I/O remains a signifi- cant performance challenge, particularly in the case of disk storage. With file systems, performance is also an issue. Other design requirements, such as reliability and security, also come into play. From a user's point of view, the file system is perhaps the most important aspect of the operating system:The user wants rapid access to files but also guarantees that the files will not be corrupted and that they are secure from unauthorized access. ROAD MAP FOR PART FIVE Chapter 11 I/O Management and Disk Scheduling Chapter 11 begins with an overview of I/O storage devices and the organization of the I/O function within the operating system.This is followed by discussion of vari- ous buffering strategies to improve performance. The remainder of the chapter is devoted to disk I/O. We look at the way in which multiple disk requests can be scheduled to take advantage of the physical characteristics of disk access to improve response time.Then we examine the use of a disk array to improve performance and reliability. Finally, we discuss the disk cache. Chapter 12 File Management Chapter 12 provides a survey of various types of file organizations and examines op- erating system issues related to file management and file access. It discusses physical and logical organization of data. It examines the services relating to file manage- ment that a typical operating system provides for users. It then looks at the specific mechanisms and data structures that are part of a file management system. Input/Output and Files 494 M11_STAL6329_06_SE_C11.QXD 2/21/08 9:33 PM Page 494 I/O M ANAGEMENT AND D ISK S CHEDULING 11.1 I/O Devices 11.2 Organization of the I/O Function The Evolution of the I/O Function Direct Memory Access 11.3 Operating System Design Issues Design Objectives Logical Structure of the I/O Function 11.4 I/O Buffering Single Buffer Double Buffer Circular Buffer The Utility of Buffering 11.5 Disk Scheduling Disk Performance Parameters Disk Scheduling Policies 11.6 Raid 11.7 Disk Cache Design Considerations Performance Considerations 11.8 UNIX SVR4 I/O Buffer Cache Character Queue Unbuffered I/O UNIX Devices 11.9 LINUX I/O Disk Scheduling Linux Page Cache 11.10 Windows I/O Basic I/O Facilities Asynchronous and Synchronous I/O...
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