Understanding Computer Storage: Memory vs. Storage Devices and Mediums - Prof. Wooyoung Ki, Study notes of Computer Science

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Copyright: Louise Henry at GSU - CS Chapter 7: Storage Memory Versus Storage What is storage?  Media and devices used to store and retrieve data, instructions, and information How does storage differ from memory?  (Memory is also called primary storage or RAM)  Storage (also called secondary storage):  Stores items for future use, rather than temporarily  Storage is nonvolatile, rather than volatile  When you want to work with a file, you read it from storage and place it in memory  When you are finished with the file, you write it from memory into storage How does volatility compare?  Screen display and contents of most RAM (memory) erased when power is off  Contents of storage retained when power is off What is a storage device and a storage medium?  Storage device o Hardware that records and retrieves items to and from a storage medium  Storage medium o Physical material on which a computer keeps data, instructions, and information What is reading and writing?  Reading o Process of transferring data, instructions, and information from a storage medium into memory o Serves as a source of input  Writing o Process of transferring items from memory to a storage medium o Serves as a source of output What is access time?  Amount of time it takes device to locate item on disk  Defines speed of disk storage device o Tape (slowest, least expensive) o Floppy Disk Page 1 of 25 o Compact Disc o Hard Disk What is capacity?  Number of bytes (characters) storage medium can hold o Kilobyte KB – 1 thousand o Megabyte MD – 1 million o Gigabyte GB – 1 billion o Terabyte TB – 1 trillion o Petabyte PB – 1 quadrillion Floppy Disks What is a floppy disk?  Portable, inexpensive storage medium  Today’s standard disk is 3.5” wide  HD (High Density disk) Stores 1.44MB What are the parts of a floppy disk?  Thin, circular, flexible film enclosed between two liners How are floppy disk drives designated?  One floppy drive o drive A  Two floppy drives o drive A o drive B How does a floppy disk drive work?  1: Shutter moves to expose recording surface on disk  2: Signal sent to control movement of read/write heads and disk  3: If write instruction, circuit board verifies whether disk can be written to  4: Motor causes floppy disk to spin  5: Motor positions read/write heads over correct location on disk  6: Read/write heads read data from or write data on the floppy disk What are tracks and sectors?  Track is narrow recording band that forms full circle on disk surface  Sector can store up to 512 bytes of data Page 2 of 25 What is an Internet hard drive?  Service on Web that provides storage to computer users o Most offer free storage o Revenues come from advertisers What are advantages of an Internet hard drive?  Large audio, video, and graphics files can be downloaded to an Internet hard drive instantaneously  Files can be accessed from any computer or device with Web access  Others can be authorized to access data from your Internet hard drive  Allows offsite backups of data Compact Discs What is a compact disc (CD)?  Storage medium  Most PCs include some type of compact disc drive  Available in variety of formats o CD-ROM o CD-R o CD-RW o DVD-ROM  DVD+RW How do you use a compact disc?  CD drives can read compact discs, including audio discs How does a laser read data on a compact disc?  1: Laser diode shines light beam toward compact disc  2: If light strikes pit, it scatters. If light strikes land, it is reflected back toward laser diode.  3: Reflected light deflected to light-sensing diode, which sends digital signal of 1. Absence of reflected light read as digital signal of 0. How is data stored on a compact disc?  Typically stores items in single track  Track divided into evenly sized sectors that store items  Single track spirals to edge of disc What is a jewel box?  Protective case for compact disc How should you care for a compact disc? CD-ROMs Page 5 of 25 What is a CD-ROM?  Compact disc that uses same laser technology as audio CDs for recording music  Cannot erase or modify contents (can only be read)  Typical CD-ROM holds about 650 MB  Commonly used to distribute software and games What is the data transfer rate of a CD-ROM drive?  40X o 40 X 150 KB per second = 6,000 KB per second or 6 MB per second  75X o 75 X 150 KB per second = 11,250 KB per second or 12.25 MB per second CD-R and CD-RW What is a CD-R (compact disc-recordable)?  Compact disc onto which you can record text, graphics, and audio  Write on CD-R (only once) using CD burner (recorder)  CD-R drive can read and write both audio CDs and standard CD-ROMs  Cannot erase disc’s contents What is a CD-RW (compact disc-rewritable)?  Erasable disc you can write on multiple times  Must have a CD-RW disc, CD-RW software, and CD-RW drive How is an audio CD created? DVD-ROMs What is a DVD-ROM (digital video disc-ROM)?  High capacity compact disc capable of storing from 4.7 GB to 17 GB (telephone book for USA)  Must have DVD-ROM drive or DVD player to read DVD-ROM  Primarily used for movies  Next-generation software will be delivered on DVD How does a DVD-ROM store data?  Two layers of pits are used, where lower layer is semitransparent o Laser can read through it to upper layer  Bits are closer together  Can be double-sided  DVD+RW is a rewritable DVD (similar to CD-RW)  4.7 GB – 17 GB Tapes Page 6 of 25 What is tape?  Magnetically coated ribbon of plastic capable of storing large amounts of data and information at a low cost  Primarily used for backup What is sequential access versus direct access?  Sequential access o Reading and writing data consecutively o Method used for tape  Direct access o You can locate a particular data item or file immediately o Method used for floppy disks, hard disks, and compact discs o Also called random access Enterprise Storage Systems What is an enterprise storage system?  Strategy that focuses on availability, protection , organization, and backup of storage in a company o RAID o Tape Library o CD-ROM jukeboxes PC Cards What are uses of PC Cards?  Used for notebook and mobile computing: o Type I RAM, flash memory o Type II Modem, Sound o Type III Hard disk Miniature Mobile Storage Media What is miniature mobile storage media?  Handheld devices use to augment internal storage o Memory Card o Memory Stick How is miniature storage media used?  Handheld devices, such as players and wallets, read or display contents of miniature storage media such as memory cards  Digital cameras Page 7 of 25 Chapter 8: Systems Software Composed of Operating System and Utility Programs Operating Systems What is an operating system (OS)?  Set of programs that coordinates all activities among computer hardware resources What are the functions of an operating system?  start up the computer  administer security  control a network  access the Web  monitor performance and provide housekeeping services  schedule jobs and configure devices  manage memory  manage programs  provide user interface Where is the operating system located?  operating system resides on ROM in handhelds  operating system resides on hard disk in most cases What is a cross-platform application?  One that runs identically on multiple operating systems o Windows 95, 98, 2000, ME, and XP Operating System Functions What is booting?  Process of starting or restarting a computer  Cold boot o Process of turning on a computer after it has been powered off completely  Warm boot o Process of restarting a computer that is already powered on What messages display on the screen when you boot the computer?  BIOS version and copyright notice  Total amount of memory  Devices detected and tested  Windows message  Sound card and CD-ROM drivers loaded Page 10 of 25 How does a personal computer boot up?  Step 1: Power supply sends signal to components in system unit  Step 2: The processor accesses BIOS to start computer  Step 3: BIOS checks components such as mouse, keyboard connectors, and expansion cards  Step 4: Results of POST (Power-on Self Test) are compared to data in the CMOS chip  Step 5: BIOS looks for system files in drive A (floppy disk drive) and then drive C (hard disk) o Drive that contains operating system is called boot drive  Step 6: Boot program loads kernel of operating system into RAM from boot drive o Operating system in memory takes control of computer  Step 7: Operating system loads configuration information and displays desktop on screen  Operating system executes programs in StartUp folder  Click Start to display list of applications you can run What is an emergency recovery disk?  Floppy disk that contains system files that will start computer when hard disk becomes damaged and computer cannot boot  Also called repair disk, boot disk, or rescue disk What is a user interface?  Controls how you enter data and instructions and how information displays on screen o command-line (DOS) interface o graphical (Windows) interface What is multitasking?  Allows single user to work on two or more applications that reside in memory at same time  Foreground contains active application - the one you currently are using  Background contains inactive programs that are running but are not in use o Background applications listed on taskbar What are other program management features of operating systems?  Multiuser o Operating system enables two or more users to run a program simultaneously  Multiprocessing o Operating system can support two or more processors running programs at same time  Fault-tolerant computer o Continues to operate even if one of its components fails o Computer has duplicate components such as processors, memory, and disk drives What is memory management? Page 11 of 25  Optimizes the use of random access memory (RAM) o allocates, or assigns, data and instructions to area of memory while they are being processed o monitors contents of memory o clears items from memory when processor no longer requires them What is virtual memory (VM) management?  Operating system allocates portion of hard disk to function like RAM o Paging o Thrashing (characterized by program stopped responding and hard disk’s LED blinking repeatedly) How does an operating system schedule jobs?  Adjusts schedule based on job’s priority job What is spooling?  Print jobs sent to buffer instead of directly to printer, where print jobs wait their turn o Print queue What is a device driver?  Small program that tells operating system how to communicate with a device  Each device requires its own specific driver in order to work correctly How do you install a device driver?  Use Control Panel How does an operating system monitor performance?  Provides a program, called performance monitor, that assesses and reports information about various system resources and devices How does an operating system manage files?  Includes a program called file manager, such as Windows Explorer  Functions related to storage and file management o Commands include Copy, Rename, Delete, Move, Format, and New Folder What is a file allocation table (FAT)?  A table of information that operating system uses to locate files on a disk  Reformatting disk usually erases only file allocation table and leaves actual files on disk What are features of a network operating system?  Organizes and coordinates how multiple users access and share resources  Server is computer that controls access to network and provides centralized storage area  Other computers on network are called clients How do operating systems administer security? Page 12 of 25 o Screen saver (Causes monitor's screen to display a moving image or blank screen if there is no activity for a specified time period) Chapter 8 Complete Page 15 of 25 Chapter 9: Communications and Networks Communications What are computer communications?  Process in which one computer transfers data, instructions, and information to another computer(s)  Communications system contains many types of devices o personal computers o notebook computers o Web-enabled cellular telephones o Web-enabled handheld computers o WebTV™ o GPS receivers What is needed for successful communications?  Sending Device  Communications Device  Communications Channel  Communications Device  Receiving Device What is the primary function of a communications device?  To convert digital signals to analog signals or analog signals to digital signals  Analog signal o Continuous electrical wave  Digital signal o Distinct pulses that represent bits grouped together into bytes Sending and Receiving Devices What is a sending and receiving device?  Initiates or accepts transmission of data, instructions, and information o Notebook computers o Desktop computers o Mid-range servers o Mainframe computers o Internet appliances & Web-enabled devices Uses of Communications Technologies What are some uses of communications technology? Page 16 of 25  Voice mail  E-mail  Newsgroups  Collaboration  Fax  Instant messaging  Telephony  Groupware  Chat rooms  Videoconferencing  Global positioning system (GPS) What is instant messaging (IM)?  Real-Time Internet Communications service  Notifies users when people are online so they can exchange messages o 1: Login to the IM server o 2: Server checks if any established friends, family, or co-workers, called buddies, are online o 3: Send instant messages to online buddy o 4: Instant message travels through messaging server and then to online buddy What is a chat room?  Permits users to converse in real time via the Internet  Types of chat rooms o Voice chats o Video chats o Radio chats What is a newsgroup?  Area on the Web where users conduct written discussions about a particular subject  Also called threaded discussion What is Internet telephony?  Enables you to talk to other people over the Internet What is collaboration?  Working with other users connected to a server  You can conduct online meetings  Allows you to share documents with others in real time o Microsoft’s NetMeeting allows collaboration Page 17 of 25  LAN technology that controls access to network by requiring network devices to share or pass a special signal, called a token  Device with token can transmit data over network  Only one token exists per network  Based on ring topology, although it can use star topology What is TCP/IP?  Short for Transmission Control Protocol/Internet Protocol  Transmits data by breaking it up into packets  Commonly used for Internet transmissions  Packets o Data divided into small pieces called packets  Routers o Devices that direct packets along fastest available path  Packet switching o Technique of breaking a message into packets, sending packets, and then reassembling data What is the Wireless Applications Protocol (WAP)?  Allows wireless mobile devices to access Internet and its services o Web o E-mail  Wireless device contains client software, which connects to Internet service provider's server What is an intranet?  Internal network that uses Internet technologies  Lets company make information accessible to employees and facilitate working in groups  Typically includes a connection to Internet o Has a Web server o Accessible via a Web browser o Users can post and update information on intranet by creating and posting a Web page What is an extranet?  Allows customers or suppliers to access part of company’s intranet What is a firewall?  Hardware and/or software that restricts access to data and information on network What is a home network?  Ways to connect o Ethernet – connect each computer via cable Page 20 of 25 o HomePLC (powerline cable) – use electrical lines in house o Phoneline – use telephone lines o HomeRF (radio frequency) – wireless What is an intelligent home network?  Extends basic home network to include features such as lighting control, thermostat adjustment, and security system Communications Software What is communications software?  Programs that help establish connection to another computer or network What is file transfer protocol (FTP)?  Internet standard that allows you to upload and download files to and from a Web server, called the FTP server The Telephone Network What is the public switched telephone network (PSTN)?  Worldwide telephone system that handles voice-oriented telephone calls o Analog Signal from home or office o Most of the PSTN uses digital technology What is a dial-up line and a dedicated line?  Dial-up line is temporary connection using telephone line for communications  Dedicated line is line always connected between two communications devices  Advantages of dial-up line o 1. Costs no more than making regular call o 2. Computers at any two locations can establish a connection using modems and telephone network  Advantages of dedicated line o 1. Quality and consistency of connection are better o 2. Computer locations are fixed o 3. Can be digital or analog What is transfer rate?  Speed at which a line carries data and information  Faster the transfer rate, the faster you can send and receive data and information  Usually expressed as a measure of bits per second o bps - bits per second Page 21 of 25 o Kbps - kilobits per second o Mbps - megabits per second o Gbps - gigabits per second What are popular types of digital dedicated lines?  ISDN (Integrated Services Digital Network) o Standards for digital transmission o Over standard copper telephone lines  Cable TV  DSL (Digital Subscriber Line)  T-carrier o Digital Line o Carries multiple signals over a single communications line o T1 line is the most popular  ATM (Asynchronous transfer mode) Communications Devices What is a communications device?  Any type of hardware capable of transmitting data, instructions, and information between sending device and receiving device o Dial-up modems o ISDN and DSL modems o Cable modems o Network interface cards What is a dial-up modem?  Communications device that converts computer's digital signals to analog signals and analog signals to digital signals  Mo + dem o Modulate  To convert a digital signal into an analog signal o Demodulate  To convert an analog signal into a digital signal  ISDN and DSL use digital modem with a digital telephone line What is a cable modem?  Modem that sends and receives data over cable television network Page 22 of 25