Understanding Data Storage: Media, Devices, and File Systems - Prof. Willis Boughton, Study notes of Computer Science

Download Understanding Data Storage: Media, Devices, and File Systems - Prof. Willis Boughton and more Study notes Computer Science in PDF only on Docsity! 1 Chapter 3 1 Storage medium (what data is stored on) Floppy disk, CD or DVD, etc. Can be removable or nonremovable from the storage device Storage device (device into which storage medium is inserted to be used) Floppy disk drive, CD or DVD drive, etc. Devices on Microsoft Windows are identified by name or letter a: device is floppy c: device is main disk drive Can be internal, external, or remote 2 Logical file representation (logical file system): refers to the user s view of the way data is stored What you see in Windows Explorer File: something stored on a storage medium, such as a program, document, or image Filename: name given to a file by the user Folder: named place on a storage medium into which files can be stored Shortcut (Microsoft Windows): a file that is a link to another file (an "alias" for another file) Physical file representation: physical way the data is stored on the media as viewed by the computer 5 Logical File Representation : Fle Edt View Favortes Tools Hep a” Fis | Gas Qh Psd pram | OT + Address le Documents and Settings Debbie My Docunents¥) Eco | Folders x Name eee ee (B vesto A) 140 Industries Proposal Meno- May 2007. doc — = E}eydoaents — Sek Day procedre meno Nov 2007.doc Hom 18 | BB Budgets Bl statt Evaluations Memo,doc Memos folder. oma 2 | fille 2 Se y Folders; Memos folder is selected, Explorer demo Magnetic: Data is stored magnetically; the data (0s and 1s) is represented using different magnetic alignments Floppy and hard disk Optical: Data stored as optical marks made by laser beam CDs and DVDs Electronic: Data stored electronically Flash memory (called memory but in fact is storage) 7 Floppy Disks A write-protect square can prevent accidentally writing to the disk; the square’s plastic window can be opened (for write- protection) and closed (for data storage) with your fingernail. Ahard plastic cover protects the disk from dirt and damage. A spring-loaded shutter ee exposes the surface of a disk so it can be read from. Liners remove dirt from the disk’s surfaces as it spins. A label can be placed on the disk to indicate its contents. The plastic surfaces of the disk are coated a with a magnetizable substance so that data can be recorded. A metal hub at the center of the disk is used to spin the disk inside the drive. 10 Low capacity, random access, removable magnetic disk made of flexible plastic permanently sealed inside a hard plastic cover Only 1.44 MB capacity Very slow Floppy disk drive: storage device that reads from and writes to floppy disks Sometimes referred to as a legacy drive and not included on all new PCs today Can buy external floppy drive and connect via USB 11 Physical file representation consists of tracks, sectors, and clusters Logical file system is installed by formatting Must be done before first use File system is always FAT 12 Physical file representation consists of tracks, clusters, sectors, and cylinders (pp 103) Logical file system installed by formatting Must be done before disk is first used Windows file system is usually NTFS. Read/write heads "fly" above spinning platters much like airplanes "Head crash" is when a head touches a platter Permanently ruins disk (pp 104) Platters hermetically sealed in disk body since a single grain of dust can cause head crash 15 Disk access time: time that it takes for a drive to start to read or write a file Depends on how fast the disk spins and how fast the read/write heads can move Typically about 10 ms (0.01 sec) Hard disk cache: RAM used to temporarily store data being read or written Greatly improves disk performance since data already in cache can be retrieved much faster RAM is on the motherboard or disk adapter card - not main memory 16 Dividing one hard disk into separate areas called partitions or logical drives One disk could have c:, d:, and e: drives, for example Used for: Installing more than one operating system Creating a recovery partition - restore system if main partition becomes unusable Creating separate partitions for programs and data Partitions demo 17 External hard drives: connect to an external port, usually USB, FireWire, or PC Card Drive can be moved from one PC to another Good for backup purposes May be slower and less reliable than internal drive Portable hard drives: designed to be carried around Good for backup purposes Less capacity and more expensive Either external or portable likely will break if dropped 20 Superdiskettes: High-capacity diskettes essentially Most widely used holds 100, 250, or 750 MB Proprietary (can only be used with their drive) Disappearing quickly - no advantages any more Hard disk cartridges: Removable hard disk that slides in and out of drive High capacity, like any hard drive, but proprietary 21 Optical discs (CDs and DVDs) store data optically using laser beams, not magnetically or electronically Typically 4½-inch in diameter, although smaller discs and custom shapes are also available Divided sectors like magnetic disks but with a single spiral track You do not format Uses either one side only or both sides of disk Can be read-only, recordable (write once), or rewritable (write many times) Capacity 650 MB or more (about 1 hour of music) 22 Can be read only, not written to CD-ROM (compact disc read-only memory) disc Usually holds about 650 MB Supported on every PC and every Mac Used to distribute software and audio CDs DVD-ROM (digital versatile disc read-only memory) disc Holds 4.7 GB (single-sided); 8.5 GB (double-sided) Used for video DVDs 25 Recordable Optical Discs, Cont'd RECORDABLE DVD+R DL DISC Dual-layer disc—holds 8.5 GB. REWRITABLE DVD-RAM DISC Holds 9.4 GB. REWRITABLE CD-RW DISC Single-layer disc—holds 650 MB. SONY a REWRITABLE BLU-RAY DISC. Holds 23.3 GB. 26 Can be recorded on, erased, and overwritten many times Unlike a magnetic disk, can overwrite only a limited number of times before disk fails More expensive than recordable discs Most common: CD-RW, DVD-RW, and DVD+RW discs 27 Flash Memory, Cont'd | = rd Ey LS PS = = ij Sy COMPACTFLASH CARD XD PICTURE CARD Samisk “4 Ait ‘ FLASH MEMORY CARD READER 1 O.: | This reader connects to a USB port and can be used with several different types of flash memory media. SECURE DIGITAL (SD) CARD MEMORY STICK 30 Flash memory drive: flash memory media and a reader in a single self-contained unit Typically portable drives that connect via a USB port Also called USB mini drives, USB flash drives, thumb drives, jump drives, and key drives Flash memory hard drives (solid state memory disks or SSDs) that use flash memory instead of magnetic media are also available Much more expensive than equivalent magnetic hard drive 31 Network storage: on a hard disk on a local network Online storage: on an Internet web site Upload to website using browser or FTP program Both used for: Backup Transferring files to others or to another PC Sharing files with others (online photo sites, etc.) 32 fl EU | Report] ee } tte 7 STRIPING When a file is written to a RAID system using striping, it is split among multiple drives. Cute MIRRORING When a file is written to a RAID system using mirroring, an identical copy of the file is sent to another drive in the system. 35 Smart card: credit card-sized piece of plastic that contains computer circuitry (processor, memory, and storage) Store small amount of data: 256 KB or less Commonly used to store prepaid amounts of digital cash or personal information Smart card readers are built into or attached to a PC, keyboard, vending machine, or other device Some smart cards store biometric data 36 Smart Cards, Cont'd CONVENTIONAL SMART CARDS Used to store and retrieve personal information, as well as pay for items using digital cash loaded onto the card. Smart card Smart card circuitry HIGH-CAPACITY SMART CARDS The StorCard smart card shown here contains a magnetic disk inside the card to increase S to rCa ge) storage capacity to 100 MB. i ee 37