Chapter 8 Secondary Storage

Competencies (Page 1 of 2) Distinguish between primary & secondary storage Describe the traditional floppy disk and compare it to high capacity floppy disks Compare internal hard disks, hard-disk cartridges, and hard-disk packs Page 210

Competencies (Page 2 of 2) Describe ways to improve hard-disk operations, including disk caching, redundant arrays of inexpensive disks, and data compression and decompression Discuss the different types of optical disks; mass storage Describe solid-state storage, Internet drives, and magnetic tape Page 210

Storage RAM Primary storage Secondary storage Volatile Temporary Secondary storage Nonvolatile Permanent Secondary storage characteristics Media Capacity Storage devices Access speed Secondary storage permanently saves information for future use; to share information with others; to modify at later date Secondary storage is nonvolatile – stores programs and data as opposed to temporary storage (RAM) Characteristics include: Media or medium – actual physical materials that holds the data and programs Capacity – measures how much a particular storage medium can hold Storage devices – hardware that reads data and programs from storage media (most also write to storage media) Access speed or access time – measures the amount of time required by the storage device to retrieve data and programs RAM Page 212

Secondary Storage Devices Most desktop microcomputer systems have floppy disks, hard disks, and optical disk drives Floppy disk – inexpensive and removable Optical disks – large storage capacity Hard disk – large storage capacity and fast retrieval times Page 212

Traditional Floppy Disk Also known as: Diskettes Floppies Portable storage media Floppy disk drives (FDD) Insert Art Work top of page 213 Floppy disks are removable storage media. Today’s standard is 1.44 MB. Data recorded in rings called called tracks; tracks divided into wedge-shaped sections called sectors Most disks manufactured currently preformatted w/tracks and sectors While called floppy, actually pieces of flat Mylar rotating within a hard plastic jacket The bits of data are represented by the presence or absence of magnetic charges Storage capacities range from 360 KB to 1.44 MB Write-protect notch or window to prevent inadvertent erasure or write-over Density refers to how tightly the bits can be packed next to one another; common density is 2HD A shutter on the disk slides to the side to expose the recording surface Labels provide an area to write or document the contents of the disk Page 212

High Capacity Floppy Disks Known as a floppy-disk cartridge Require special disk drives Three well known types Zip disks HiFD disks SuperDisks Zip disks – usually manufactured by Iomega; 100 MB, 250 MB, or 750 MB worth of storage; requires own drive HiDF disks – usually manufactured by Sony Corp; 200 MB or 750 MB capacity Biggest advantages: can use HiDF disk in floppy drive; popular with notebooks Super disks – usually manufactured by Imation; 120 MB or 240 MB capacity; SuperDisk disk drives can use standard floppy disks Zip disks – 100 MB, 250 MB or 750 MB HiFD disks - 200MB or 720MB SuperDisks – 120 MB or 240 MB Page 214

Hard Disks Use thicker, metallic platters for storage Faster than a floppy diskette Large capacity Sensitive instruments There are three types of hard disks: Internal Hard-disk cartridge Hard-disk pack Composed of metallic rather than plastic disks Platters – rigid metallic, stacked one on top of another Fast information storage and retrieval Read-write head is .000001 inch above surface An internal hard disk is also known as a fixed disk Page 215

Materials that Cause a Head Crash Head crash is a disaster for a hard disk Head crashes occur when the read-write head contacts with the disk surface or with particles on the disk's surface Head crashes are now rare A smoke particle, human hair, or fingerprint could cause a head crash Return Page 215

Internal Hard Disk Located inside system unit Known as a fixed disk Designated as the C drive Advantages over floppies Access speed Capacity Located inside the system unit; also known as fixed disk Used for storing the operating system, other programs, and large data files You should perform routine maintenance and periodically backup all important files Page 215

Optical Disks Compact Permanent storage Laser beams reflect off pits Two common types CD DVD Use laser technology. CD and DVD are optical disk formats. Compact, high capacity form of permanent storage (up to 17 gigabytes of data) Laser beam writes by creating a pattern of pits (holes) and lands (flat areas) to encode data bits Laser beams reflect off the pits and lands to read the data Optical disks come in many different sizes Most common is 4 ¾ inches Stored in a protective case called jewel boxes Page 219

Compact Disc Optical format From 650 MB to 1 GB capacity Rotation speeds vary Types Read only: CD-ROM Write once: CD-R Rewriteable: CD-RW Picture CDs and Photo CDs CD stands for compact disc Standard on most computers; can store from 650 MB up to 1 GB Speed determines how fast data can be transferred Read only: CD-ROM Commercial music CD Read only means it cannot be written on or erased Used to distribute large databases and references Write once: CD-R (CD-recordable) Known as burners Used to archive data or to record music downloaded from the Internet Rewriteable: CD-RW Known as erasable optical disks Can be changed Used to create and edit multimedia presentations Picture CDs and Photo CDs Special format developed by Eastman Kodak to store digital images Two types: Single-session or multisession Ideal for use as permanent data archives for essential company information Page 219

Digital Versatile Disc Digital Versatile Disk or Digital Video Disk (DVD) Similar to CDs, but can store more data Types Read only: DVD-ROM Write once: DVD+R; DVD-R Rewritable: DVD+RW; DVD-RW; DVD-RAM DVD-ROM Known as DVD players Used for videos DVD-R and DVD+R Two competing write once formats Write once format Used to create permanent archives for large amounts of data and to record videos DVD-RAM or DVD-RW – rewritable version DVD-RW DVD+RW DVD-RAM Each format has a unique way of storing data; older DVD players can’t read all formats but the new DVD players can Rapidly replacing the CD rewritable drives Use to store video from camcorders and developing large multimedia presentations that include extensive graphics and video Page 220

Other Types of Secondary Storage Solid-state storage Internet hard drives Magnetic tape Solid-state storage No moving parts Reliable, but expensive Internet hard drives Low cost Flexibility to access information from any location using the Internet Slower access speed Magnetic tape Slower sequential access Stores data and programs Used for making backups of data Page 221

Solid-State Storage Flash memory cards Key chain hard drives Widely used in notebook computers Used to record MP3 music files Key chain hard drives Key chain flash memory devices Connects to a USB port Key chain hard drives have recently been introduced Very compact Worn as a necklace or on a key ring Connect to a USB port Predicted that they will replace the floppy disk for transporting data Capacities up to 1 GB Return Page 221

Internet Hard Drives Known as i-drive or online storage Return These are Web sites that provide storage space Not used for storing highly personalized or sensitive information Return Page 224

Magnetic Tape External storage Provides sequential access Information stored in sequence Slower than disks which provide direct access Magnetic tape streamers or tape cartridges used by both mainframes and microcomputers Sequential access because they have to be fast forwarded or rewound before a specific location can be reached A common sequential access method of permanent storage method Common form of data backup in companies with larger computer systems; magnetic disk offer fast, direct access to data programs Two forms of tape storage Magnetic tape streamers Backup tape cartridge units used with microcomputer systems Capacities range from 120 MB to 5 GB Return Page 225