Module 14 - Tertiary storage structure. In this chapter introduced the concept of primary, secondary, and tertiary storage. In this chapter, we discuss tertiary storage in more detail. First we describe the types of storage devices used for tertiary storage. Next, we discuss the issues that arise when an operating system uses tertiary storage. Finally, we consider some performance aspects of tertiary storage systems. | Lecture Operating system concepts Fifth edition Module 14 - Avi Silberschatz Peter Galvin Module 14 Tertiary-Storage Structure Tertiary Storage Devices Operating System Issues Performance Issues Silberschatz and Galvin 1999 Tertiary Storage Devices Low cost is the defining characteristic of tertiary storage. Generally tertiary storage is built using removable media Common examples of removable media are floppy disks and CD-ROMs other types are available. Silberschatz and Galvin 1999 Removable Disks Floppy disk thin flexible disk coated with magnetic material enclosed in a protective plastic case. Most floppies hold about 1 MB similar technology is used for removable disks that hold more than 1 GB. Removable magnetic disks can be nearly as fast as hard disks but they are at a greater risk of damage from exposure. Silberschatz and Galvin 1999 Removable Disks Cont. A magneto-optic disk records data on a rigid platter coated with magnetic material. Laser heat is used to amplify a large weak magnetic field to record a bit. Laser light is also used to read data Kerr effect . The magneto-optic head flies much farther from the disk surface than a magnetic disk head and the magnetic material is covered with a protective layer of plastic or glass resistant to head crashes. Optical disks do not use magnetism they employ special materials that are altered by laser light. Silberschatz and Galvin 1999 WORM Disks The data on read-write disks can be modified over and over. WORM Write Once Read Many Times disks can be written only once. Thin aluminum film sandwiched between two glass or plastic platters. To write a bit the drive uses a laser light to burn a small hole through the aluminum information can be destroyed by not altered. Very durable and reliable. Read Only disks such ad CD-ROM and DVD com from the factory with the data pre-recorded. Silberschatz and Galvin 1999 Tapes Compared to a disk a tape is less expensive and holds more data but random .
