8 SECONDARY STORAGE CHAPTER Secondary storage devices are used to save, to back up, and to transport files Over the past several years, data storage capacity has expanded from saving numbers and text to include digital images and video Competent end uses need to know the capabilities, the limitations, and the uses of floppy disks, hard disks, opticak disks, and other types of secondary storage

Storage RAM Primary storage Secondary storage Volatile Temporary Secondary storage Nonvolatile Permanent Secondary storage characteristics Media Capacity Storage devices Access speed Permanently save information for: future use; to share info with others; to modify at later date Secondary storage is nonvolatile – stores programs and data as opposed to temporary storage (RAM) RAM

Secondary Storage Devices Floppy disk – inexpensive and removable Optical disks – large storage capacity Hard disk – large storage capacity and fast retrieval times

Traditional Floppy Disk Floppy Disks Diskettes Floppies Portable storage media Floppy disk drives (FDD) Traditional Floppy Disk 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

Traditional Floppy Diskette 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 A shutter on the disk slides to the side to expose the recording surface

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

Hard Disks Use thicker, metallic platters for storage Faster than a floppy diskette Large capacity Sensitive instruments Composed of metallic rather than plastic disks Fast information storage and retrieval Read-write head is .000001 inch above surface An internal hard disk is also known as a fixed disk

Materials that Cause a Head Crash Head crashes occur when the read-write head contacts 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

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

Hard-Disk Cartridges Removable hard disks Used to complement internal hard disk Large capacity PC Card Hard Disks Capacity limited only by number of cartridges; used to complement internal hard disk. PC Card hard disk available for notebooks with a capacity of up to 5 GB Popular vendors: Iomega and Peerless

Hard-Disk Packs Removable Massive storage capacity Common in mainframes Massive storage capacity Common in mainframe systems Composed of a larger number of platters, resembling a stack of record albums Most platters offer read-write surfaces on top and bottom Access time - time between the computer’s request for data from secondary storage and the completion of the data transfer; usually access time is faster with this type of secondary storage

Hard-Disk Pack Removable storage devices Multiple recording platters aligned one above the other Found on mainframes Hard-disk packs are stored in a hard plastic cover that is removed when mounted onto a special drive

Performance Enhancements Disk caching Redundant arrays of inexpensive disks (RAID) File compression and decompression Disk caching Uses hardware and software to anticipate data needs Frequently used data is stored in memory; when needed, the access time is much faster Redundant arrays of inexpensive disks (RAID) Groups of low cost hard-disk drives grouped together using networks and special software Performs as a single large-capacity disk; but faster than a single disk of comparable size File compression and decompression Increase storage capacity Reduce space required for storage; reduce up to ¼ of original size WinZip and PKZip are well-known programs

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

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 can't 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 Multi-session Ideal for use as permanent data archives for essential company information

Digital Versatile Disc Digital Versatile Disk or Digital Video Disk (DVD) Similar to CDs, but can store more data Types Read only Write once Rewritable DVD-ROM Known as DVD players Used for videos DVD-R and DVD+R Two competing write once formats Write once format Expensive and not widely used DVD-RAM or DVD-RW - rewritable version DVD-RW DVD+RW DVD-RAM

DataPlay Optical disk Write once format Quarter size 500 MB capacity Holds 5 hours of CD-quality sound Use for storing and playing music files Optical write once format similar to CD-R Size of a quarter Used to store music Harder to copy Music industry is supporting this format

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 Magnetic tape Slower sequential access Stores data and programs Used for making backups of data

Solid-State Storage Flash memory cards Key chain hard drives Widely used Can be 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

Internet Hard Drives These are Web sites that provide storage space Also called i-drive or online storage Not used for storing highly personalized or sensitive information

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 Magnetic disk offer fast, direct access to data programs; 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 *Two forms of tape storage Magnetic tape streamers Backup tape cartridge units used with microcomputer systems Capacities range from 120 MB to 5 GB Digital audio tape (DAT)

The End of Chapter 8