Understanding Computers Ch.41 Chapter 4 Storage

Understanding Computers Ch.42 Learning Objectives Explain the difference between storage systems and memory. Name several general properties of storage systems. Identify the two primary types of magnetic disk systems and describe how they work. Discuss the various types of optical disc systems available and how they differ from each other and from magnetic systems.

Understanding Computers Ch.43 Overview This chapter covers: Common characteristics of storage systems Magnetic disk storage systems Optical disc storage systems

Understanding Computers Ch.44 Properties of Storage Systems: Storage Devices and Media Involve two physical parts: a storage device and a storage medium. Can be internal (located inside the system unit), or external (located outside the system unit). Storage devices are identified by names and/or letters (e.g. C for first hard drive).

Understanding Computers Ch.45 Properties of Storage Systems: Non-Volatility Storage media are non-volatile: When power to the device is shut off, data stored on the medium remains. This is in contrast to most types of memory, which are volatile.

Understanding Computers Ch.46 Properties of Storage Systems: Removable vs. Fixed Media Fixed media: typically faster and less expensive. Removable media: unlimited capacity and can be easily transported and secured.

Understanding Computers Ch.47 Properties of Storage Systems: Random vs. Sequential Access Random access ( direct access ): data can be retrieved in any order, independent of its physical location (most types of storage media). Sequential access: data can be retrieved only in the same sequence in which it is physically stored (magnetic tape).

Understanding Computers Ch.48 Properties of Storage Systems: Logical vs. Physical Representation Logical file representation refers to the users view of the way data is stored (filename, folders, etc.). Physical file representation is the actual physical way the data is stored on the storage media as viewed by the computer.

Understanding Computers Ch.410 Magnetic Disk Systems Magnetic disks are the most widely used storage medium in computers today. Data is stored by magnetizing particles on the storage medium. Two common types: Floppy disks Hard disks

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Understanding Computers Ch.412 Floppy Disks and Drives Floppy disk characteristics Typically 3½ inches in diameter. Typically hold 1.44 megabytes. Inserted into floppy disk drive to be read from or written to.

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Understanding Computers Ch.414 Floppy Disks and Drives, Contd. Disk is divided into tracks, sectors, and clusters. The disks file directory keeps track of the contents of the disk so files can be retrieved (by filename) at a later time.

Understanding Computers Ch.415 Floppy Disks and Drives, Contd. Using floppy disks Must be inserted into the proper drive in the proper direction. Should not be removed when the disk is being accessed. High-capacity removable magnetic disks and drives Zip disks (750 MB) SuperDisks (240 MB)

Understanding Computers Ch.416 Hard Disk Drives Hard drive characteristics Metal disk onto which data is stored magnetically. Disks are usually permanently sealed inside the hard driveallows faster speeds and storage of more data than removable systems. Can be internal or external.

Understanding Computers Ch.418 Hard Disk Drives, Contd. Hard drive characteristics, contd Organized into tracks, sections, clusters, and cylinders (the collection of tracks located in the same location on a set of hard disk surfaces). Read/write head doesnt touch the surface of the disk. Bumping PC when disk is being accessed or dust or other obstacles on a hard-disk system can cause a head crash and damage the surface of the disk.

Understanding Computers Ch.419 Hard Disk Drives, Contd. Disk access time. Factors: seek time, rotational delay, data movement time Can use multiple partitions. Disk cachestrategy for speeding up system performance. Hard drive standards (EIDE, SCSI, Fibre Channel, USB).

Understanding Computers Ch.420 Hard Disk Drives, Contd. Portable hard drive systems Offer large storage capacities and portability. Either entire drive or just hard disk cartridge is transported.

Understanding Computers Ch.421 Hard Disk Drives, Contd. Storage systems for large computer systems and networks Storage servers containing racks of hard drives. Network attached storage (NAS). Storage area networks (SANs). RAID (for increased performance and/or fault tolerance).

Understanding Computers Ch.422 Optical Disc Systems Laser beams write and read data packed at very tight storage densities, many times finer than that of a typical magnetic disk. Are typically 4½-inch discs, but can be a variety of shapes and sizes. Data is stored optically on a continuous spiral track. Can be CDs or DVDs.

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Understanding Computers Ch.424 Read-Only Discs: CD-ROM and DVD- ROM Discs CD-ROM discs cannot be written to or erased and typically hold 650 MB (e.g. music CDs). DVD-ROM discs are similar to CD-ROM discs, but have higher capacity of 4.7 GB to 17 GB (e.g. movie DVDs). Data is stored by burning pits into the disc surface that can be read using a laser beam.

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Understanding Computers Ch.426 Other Types of Storage Systems, Contd Flash memory media Chip-based storage. Solid state storage systemhas no moving parts, so are more shock-proof and portable than conventional storage systems. Commonly used with digital cameras, digital music players, handheld PCs, notebook computers, smart phones, etc.

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Understanding Computers Ch.428 Other Types of Storages Systems, Contd Magnetic tape systemsplastic tape that is magnetized to represent data. Used primarily for backup and archival purposes (sequential access only). Read from and written to via a tape drive. Most tape media are in the form of cartridge tapes, though detachable-reel tapes exist as well.

Understanding Computers Ch.429 Other Types of Storage Systems, Contd Remote storage storage devices that are not directly connected to your PC. Network storage accessible through a local network. Online storage accessible via the Internet and used for back up, as well as to transfer files to others.

Understanding Computers Ch.431 Comparing Storage Alternatives Factors to consider: speed, expense, portability, storage capacity, and compatibility. Most PC users require: Hard drive CD or DVD drive Floppy drive Additional devices (flash memory card reader, etc.) as needed for the devices being used in conjunction with the PC (e.g. digital camera)

Understanding Computers Ch.432 Summary Properties of storage systems Magnetic disk systems Optical disc systems Other types of storage systems Comparing storage alternatives