Chapter 3

1. Chapter 3 Storage

2. 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.

3. 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).

4. 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.

5. 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.

6. 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).

7. 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.

8. 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

10. 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.

12. 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.

13. 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)

14. 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.

16. 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.

17. 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) .

18. 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.

19. 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).

20. 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.

22. 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.

24. 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.

25. 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.

27. Other Types of Storage Systems • Magneto-optical discs • A combination of magnetic and optical technology. • Can store up to 9.1 GB per disk.

28. Other Types of Storage Systems, Cont’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.

29. Other Types of Storage Systems, Cont’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.

31. Other Types of Storages Systems, Cont’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.  

32. Holographic Storage Systems • 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 .

33. Holographic Storage Systems, cont’d • 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) Source: http://www.inphase-technologies.com/products/markets.asp?subn=3_3

34. Other Types of Storage Systems, 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.

35. Other Types of Storage Systems, Cont’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.

37. 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)