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Chapter 3. Storage. Overview. This chapter covers: Common characteristics of storage systems Magnetic disk storage systems Optical disc storage systems Other types of storage, such as flash memory, magnetic tape, remote storage, smart cards, Solid State Drives, and Holographic storage.

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Chapter 3

Chapter 3



  • This chapter covers:

    • Common characteristics of storage systems

    • Magnetic disk storage systems

    • Optical disc storage systems

    • Other types of storage, such as flash memory, magnetic tape, remote storage, smart cards, Solid State Drives, and Holographic storage.

Properties of storage systems storage devices and media
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).

Properties of storage systems non volatility
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.

Properties of storage systems removable vs fixed media
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.

Properties of storage systems random vs sequential access
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).

Properties of storage systems logical vs physical representation
Properties of Storage Systems: Logical vs. Physical Representation

  • Logical file representation refers to the user’s 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.

Magnetic disk systems
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

Floppy disks and drives
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.

Floppy disk geometry
Floppy Disk Geometry

  • Disk is divided into tracks, sectors, and clusters.

  • The disk’s file directorykeeps track of the contents of the disk so files can be retrieved (by filename) at a later time.

Floppy disks and drives cont d
Floppy Disks and Drives, Cont’d.

  • 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)

Hard disk drives
Hard Disk Drives

  • Hard drive characteristics

    • Metal disk onto which data is stored magnetically.

    • Disks are usually permanently sealed inside the hard drive—allows faster speeds and storage of more data than removable systems.

    • Can be internal or external.

Hard disk drives cont d
Hard Disk Drives, Cont’d.

  • Hard drive characteristics, cont’d

    • 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 doesn’t 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.

Hard disk drives cont d1
Hard Disk Drives, Cont’d.

  • Disk access time.

    • Factors: seek time, rotational delay, data movement time

  • Can use multiple partitions.

  • Disk cache—strategy for speeding up system performance.

  • Hard drive standards (EIDE, SCSI, Fibre Channel, USB) .

Hard disk drives cont d2
Hard Disk Drives, Cont’d.

  • Portable hard drive systems

    • Offer large storage capacities and portability.

    • Either entire drive or just hard disk cartridge is transported.

Hard disk drives cont d3
Hard Disk Drives, Cont’d.

  • 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).

Optical disc systems
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.

Read only discs cd rom and dvd rom discs
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.

Recordable discs cd r dvd r and dvd r discs
Recordable Discs: CD-R, DVD-R, and DVD+R Discs

  • Recordable discs can be written to, but not erased or rewritten.

  • Burning a CD or DVD permanently records data onto the disc.

  • CD-R discs are commonly used to store data and for custom music CDs.

  • DVD-R/DVD+R discs are commonly used for home movies and other high-capacity applications.

Rewritable discs cd rw dvd rw dvd rw dvd ram bd rom and hd dvd rom discs
Rewritable Discs: CD-RW, DVD-RW, DVD+RW, DVD-RAM, BD-Rom and HD-DVD-ROM Discs

  • Rewritable discs can be used in the same way as magnetic disks—data can be stored and erased as needed.

  • Phase-change technology is used to record data onto the disc using reflectivity.

  • Rewritable discs can be erased by reverting the reflectivity back to the original state.

  • Blue laser discs are an emerging higher-capacity (25 GB) form of optical disc.

Other types of storage systems
Other Types of Storage Systems HD-DVD-ROM Discs

  • Magneto-optical discs

    • A combination of magnetic and optical technology.

    • Can store up to 9.1 GB per disk.

Other types of storage systems cont d
Other Types of Storage Systems, HD-DVD-ROM DiscsCont’d

  • Flash memory media

    • Chip-based storage.

    • Solid state storage system—has 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.

Other types of storage systems cont d1
Other Types of Storage Systems, HD-DVD-ROM DiscsCont’d

  • Flash memory media, cont’d.

    • Common forms of flash memory:

      • Flash memory sticks.

      • Flash memory cards—CompactFlash, Secure Digital (SD), MiniSD, MultiMedia (MMC), SmartMedia, and xD Picture cards.

      • Flash memory drives, such as USB flash drives.

Other types of storages systems cont d
Other Types of Storages Systems, HD-DVD-ROM DiscsCont’d

  • Magnetic tape systems—plastic 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.  

Holographic storage systems
Holographic Storage Systems HD-DVD-ROM Discs

  • Storing data in 3-D

  • same shape as DVD, but it stores 18-64 times as much data.

  • stores bytes throughout its depth, not just on one flat or two layers.

  • A blue laser beam burns layers at several angles

  • Drive and 300-gigabyte disks, available in 2009 form InPhase .

Holographic Storage Systems, cont’d HD-DVD-ROM Discs

  • Holographic storage system:

    • 462 CDs

    • 64 DVDs

    • 12 BDs

  • Target market is HD movie archives, data centers etc. and no consumer version.

  • Drive (also called Tapestry) is about $18,000 (about EGP 99,000) disk is about $180 (about EGP990)


Other types of storage systems cont d2
Other Types of Storage Systems HD-DVD-ROM Discs, Cont’d

  • 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 backup, as well as to transfer files to others.

Other types of storage systems cont d3
Other Types of Storage Systems, HD-DVD-ROM DiscsCont’d

  • Smart card:credit-card-sized piece of plastic that contains some type of computer circuitry.

    • Holds less than a few megabytes.

    • Commonly used to store prepaid amounts of digital cash or personal information.

    • Smart card readers are attached to a PC or built into a cell phone, keyboard, or other device.

Comparing storage alternatives
Comparing Storage Alternatives HD-DVD-ROM Discs

  • 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)