Learning Objectives

„ Explain the difference between storage systems and Chapter 4 memory.

„ Name several general properties of storage systems.

Storage „ Identify the two primary types of magnetic disk systems and describe how they work.

Learning Objectives, cont’d. Overview

„ Discuss the various types of optical disc systems „ This chapter covers: available and how they differ from each other and from magnetic systems. „ Common characteristics of storage systems

„ List at least three other types of storage systems. „ Magnetic disk storage

„ Summarize the storage alternatives for a PC, „ Optical disc storage including which storage systems should be included in all PCs and when the other systems would be appropriate. „ Magnetic tape and other types of storage systems

Properties of Storage Systems: Properties of Storage Systems: Physical Parts Nonvolatility Property

„ Involve two physical parts: a storage device and a „ Storage media are nonvolatile: storage medium.

„ When power to the device is shut off, data stored „ Can be internal (configured into the system unit), or on the medium remains. external (separate devices).

„ This is in contrast to most types of memory, which „ Media must often pass by a read/write head in the are volatile. storage device to be read from or written to.

1 Properties of Storage Systems: Properties of Storage Systems: Removable vs. Fixed Media Random vs. Sequential Access

„ Fixed media: typically faster and less expensive „ Sequential access: records in a file can be retrieved only in the same sequence in which they are physically stored (like tape) „ Removable media: unlimited capacity and can be easily transported and secured „ Direct access (random access): records can be retrieved in any sequence, independent of physical storage (most disks and optical media)

Properties of Storage Systems: Logical vs. Physical Representation

„ Logical file representation refers to the user’s view of the way data is stored.

„ 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 disks are the most important storage medium in computers today.

„ Two popular types:

„ floppy disks

„ hard disks

„ Data is written by magnetizing particles on the disks in a certain way to represent 1s and 0s.

2 Floppy Disks

„ Physical properties

„ Most are 3½ inches in diameter and hold 1.44 megabytes.

Floppy Disks, cont’d. Floppy Disks, cont’d.

„ Tracks, sectors, and clusters „ Using floppy disks

„ The disk’s file directory keeps track of the „ Must be inserted into the proper drive in the contents of the disk. proper direction

„ Should not be removed when the disk is being accessed

„ Superdiskettes

„ Zip drives, SuperDisk drives, HiFD drives

Hard Disks

„ Physical properties

„ Permanently sealed inside the hard drive—allows faster speeds than removable systems

„ Sizes: 3½-inch on PCs, 2½-inch on notebooks or smaller (IBM microdrive – size of a quarter)

„ Rotation: 5,400-15,000 revolutions per minute (RPM)

„ Types: internal or external

3 Hard Disks, cont’d. Hard Disks, cont’d.

„ Reading and writing data „ Hard disk addressing (like on diskette plus)

„ Obstacles on a hard-disk system can damage the „ Disk cylinder—the collection of tracks located in surface and read/write head. the same location on a set of hard disk surfaces

„ Movable access mechanism positions read/write heads over the surface of the platters

„ Head crash occurs if the head comes in contact with the surface of the disk

Hard Disks, cont’d. Hard Disks, cont’d.

„ Disk access time factors: „ Disk standards

„ seek time – time to position read/write heads over „ ATA/IDE – attachment/integrated drive electronics the cylinder Controller is built into drive.

„ rotational delay – time to rotate disk into proper „ SCSI – small computer system interface – position controllers are built into computers or on a special

„ data movement time – time for data transfer SCSI card. „ ATA are less expensive and easier to configure. SCSI are faster. „ Disk cache „ Fibre Channel – extremely fast (up to 2 Gbps) „ Strategy for speeding up system performance

Hard Disks, cont’d. Hard Disks, cont’d.

„ Hard disk systems for notebooks

„ Removable hard disk „ Can use either internal or removable hard drives systems

„ Offer large storage capacities and portability

4 Hard Disks, cont’d. RAID

„ Hard disk systems for large computer systems „ RAID – Redundant Array of Independent Disks

„ May use a system consisting of multiple hard „ Increases performance

drives; RAID is a recent trend „ Increases fault tolerance (ability of system to recover from hardware or software failure)

„ RAID levels from 0 to 5

„ RAID 0 – disk stripping (no fault tolerance)

„ RAID 1 – disk mirroring

Optical Discs CD fabrication

„ Laser beams write and read data packed at very tight „ The CD fabrication machine uses a high-powered storage densities, several times finer than that of a laser to etch the bump pattern into photoresist typical magnetic disk. material coated onto a glass plate

„ Through an elaborate imprinting process, this pattern is pressed onto acrylic discs

„ The discs are then coated with aluminum (or another metal) to create the readable reflective surface

„ Finally, the disc is coated with a transparent plastic layer that protects the reflective metal from nicks, scratches and debris.

General CD Structure CD pits

5 CDs CD-ROM Drive

„ CD-ROM (compact disk, read-only memory)

„ Tiny depressions on the disk are called pits

„ CDs are permanently etched when data is stored on the disc.

„ Recordable (CD-R) discs can be written to, but not erased and rewritten.

„ Rewritable (CD-RW) CDs can be used in the same way as magnetic disks—data can be stored and erased as needed.

CD-Rs CD-R (recordable)

„ CD-Rs, don't have any pits or flat areas at all

„ Instead, they have a smooth reflective metal layer, which rests on top of a layer of photosensitive dye.

„ When the disc is blank, the dye is translucent: Light can shine through and reflect off the metal surface.

„ But when you heat the dye layer with concentrated light of a particular frequency and intensity, the dye turns opaque: It darkens to the point that light can't pass through.

CD-RW (rewritable) CD-RW (rewritable) cont’d

„ CD-RW discs have taken the idea of writable CDs a step further, building in an erase function so you can record over old data you don't need anymore

„ These discs are based on phase-change technology

6 DVDs DVD types

„ DVD (Digital Versatile Disk)

„ Stores 4.7 Gb per side per layer (up to 17Gb on two-sided double-layer disks)

„ DVDs are read-only and will replace VHS as the movie media of choice

DVD-5 (Single-side, single-layer) DVD-10 (double-sided)

DVD-9 (single-sided, dual-layer) DVD-17 (double-sided, dual-layer)

7 DVD fabrication DVD Structure

„ Once the clear pieces of polycarbonate are formed, a „ Pits on DVDs are half as wide as on CDs.

thin reflective layer is sputtered onto the disc, „ Distance between pits is half as large as on CDs. covering the bumps „ The microscopic dimensions of the bumps make the „ Aluminum is used behind the inner layers, but a spiral track on a DVD extremely long semi-reflective gold layer is used for the outer layers, „ If you could lift the data track off a single layer of a allowing the laser to focus through the outer and DVD, and stretch it out into a straight line, it would onto the inner layers be almost 7.5 miles long! „ After all of the layers are made, each one is coated „ That means that a double-sided, double-layer DVD with lacquer, squeezed together and cured under would have 30 miles of data! infrared light

DVDs Recordable DVDs history

„ Recordable DVDs (2 standards + and -) „ Pioneer released 3.95G DVD-R(A) 1.0 drives allow to record once in October 1997 (about 6 months late) for $17,000 „ Rewritable DVDs (DVD-RAM or DVD+/-RW) allow users to record on DVD discs multiple times „ New 4.7G DVD-R(A) 1.9 drives appeared in limited quantities in May 1999 for $5,400

„ Pioneer's DVR-A03 DVD-R(G) drive was released in May 2001 for under $1000

Magneto-Optical Discs Magnetic Tape Systems

„ M-O discs use a combination of magnetic and optical „ Magnetic tape is used primarily for backup technologies. purposes.

„ Can store up to 5.2 GB per disc. „ The device that reads tapes is called a tape drive.

„ Most tape media are in the form of cartridge tapes, though detachable-reel tapes exist as well.

8 Online Storage

„ Online storage is usually storage on a server accessible over the Internet or another network.

„ Online storage can be used as a primary storage medium or for backup or distribution purposes.

Smart Cards Flash Memory Devices

„ Smart card: credit-card-sized piece of plastic that „ Flash memory sticks

contains some type of computer circuitry. „ Size of a stick of gum; hold from 4 to 64 MB each

„ Holds less than a few megabytes „ Flash memory cards

„ Commonly used to store prepaid amounts of „ Standards include CompactFlash, SmartMedia, digital cash, or personal information Secure Digital (SD), and MultiMedia Card (MMC)

„ Flash memory drives

„ Smart card readers are attached to a PC or built into „ Have no moving parts—are more shock-proof and a cell phone, keyboard, or other device. portable than conventional drives

Comparing Storage Alternatives

Speed, expense, portability, and compatibility

„ Most PC users require

„ Hard drive

„ CD or DVD drive

„ Floppy drive

9