1. NANJING UNIVERSITY OF INFORMATION SICENCE & TECHNOLOGY Competencies Competencies  primary storage and secondary storage  Traditional floppy disk and high-capacity floppy disks  Internal hard disks, hard-disk cartridges and hard disk packs  How to improve hard-disk performance, such as disk caching, Raid, data compression and decompression  Different types of optical discs  Solid-state storage, internal drives, and magnetic tape  Mass storage and mass storage devices Chapter 8 Secondary Storage

2. NANJING UNIVERSITY OF INFORMATION SICENCE & TECHNOLOGY Storage Storage  Primary storage devices: Memory, volatile or temporary  Secondary storage devices Provide permanent or nonvolatile storage Provide permanent or nonvolatile storage Characteristics of secondary storage: Characteristics of secondary storage: Media Media Capacity Capacity Storage devices Storage devices Access speed Access speed

3. NANJING UNIVERSITY OF INFORMATION SICENCE & TECHNOLOGY Floppy disks Floppy disks  portable and removable storage media  typically used to store and transfer relatively small data and files  use flexible flat circular pieces of Mylar plastic that coated with a magnetic material  Floppy disk drives: used to store and read data which are represented by positive and negative charges used to store and read data which are represented by positive and negative charges  Traditional floppy disk: 1.44MB, 2HD 3.5inch disk 2HD: two-side, high-density 2HD: two-side, high-density Density: how tightly the bits can be packed next to one another Density: how tightly the bits can be packed next to one another Have a thin exterior jacket made of hard plastic to protect the inside flexible disk Have a thin exterior jacket made of hard plastic to protect the inside flexible disk

4. NANJING UNIVERSITY OF INFORMATION SICENCE & TECHNOLOGY Metal Shutter: can slide to one side to expose the recording surface(Data access area) Metal Shutter: can slide to one side to expose the recording surface(Data access area) label: provide an area for users to write the contents of the disk label: provide an area for users to write the contents of the disk Write-protect notch: Write-protect notch: have a slide that opens and closes. have a slide that opens and closes. When is closed: can either read data or save file to the disk When is closed: can either read data or save file to the disk When is opened: file cannot be saved to the floppy disk When is opened: file cannot be saved to the floppy disk Format: should be formatted first before saving file to it Format: should be formatted first before saving file to it Formatting: segment the recording surface into tracks and sectors Formatting: segment the recording surface into tracks and sectors Tracks: concentric rings without visible grooves Tracks: concentric rings without visible grooves Sectors: each track is divided into invisible wedge-shaped sections called sectors Sectors: each track is divided into invisible wedge-shaped sections called sectors

5. NANJING UNIVERSITY OF INFORMATION SICENCE & TECHNOLOGY  High-capacity floppy disks Also known as floppy disk cartridges Also known as floppy disk cartridges Also 3.5 inches in diameter Also 3.5 inches in diameter however it is thicker, can store more information and requires special disk drives however it is thicker, can store more information and requires special disk drives Popular used high-capacity floppy disks Popular used high-capacity floppy disks Zip disk produced by Iomega, typically has a 100MB, 250MB, or 750MB capacity Zip disk produced by Iomega, typically has a 100MB, 250MB, or 750MB capacity

6. NANJING UNIVERSITY OF INFORMATION SICENCE & TECHNOLOGY Hard disks Hard disks  Also save files by altering the magnetic charges of the disk’s surface  However use thicker, rigid metallic platters that are stacked one on top of another  Store and organize files using tracks, sectors, and cylinders  Cylinder: a stack of overlapped platters  Could store and retrieve information much faster and have a greater capacity than floppy disks.  Read/write head: Used to read or write information on a cushion of air without contacting the hard disk’s surface  Head Crash: Head/write head makes contact with the hard disk’s surface Head/write head makes contact with the hard disk’s surface It is a disaster for a hard disk which will destroy the data. It is a disaster for a hard disk which will destroy the data.

7. NANJING UNIVERSITY OF INFORMATION SICENCE & TECHNOLOGY  Internal Hard disk: Located in the system unit and usually being divided into different partitions, such as C drive, D drive, and so on. Located in the system unit and usually being divided into different partitions, such as C drive, D drive, and so on. Have fixed amount of storage and cannot be easily removed. Have fixed amount of storage and cannot be easily removed. Mainly used to store operating system, application software and large files. Mainly used to store operating system, application software and large files. Has two advantages over floppy disks Has two advantages over floppy disks Capacity: 500GB, 700GB, 1000GB Capacity: 500GB, 700GB, 1000GB Access speed: the time required to find and retrieve information on the disk. Access speed: the time required to find and retrieve information on the disk. Hard disk rotates very faster and the read/write head is close to the recording surface, it works much faster than floppy disks. Hard disk rotates very faster and the read/write head is close to the recording surface, it works much faster than floppy disks. To ensure adequate performance and security, routine maintenance and periodic backup should be performed. To ensure adequate performance and security, routine maintenance and periodic backup should be performed.

8. NANJING UNIVERSITY OF INFORMATION SICENCE & TECHNOLOGY Features of internal hard disks Features of internal hard disks Capacity: 500GB, 700GB, 1000GB Capacity: 500GB, 700GB, 1000GB Size: 3.5inch(for desktop computer), 2.5inch(for laptop) Size: 3.5inch(for desktop computer), 2.5inch(for laptop) Rotational Speed: 5400RPM, 7200RPM, 10000RPM(Rotation Per Minute) Rotational Speed: 5400RPM, 7200RPM, 10000RPM(Rotation Per Minute) Cache: 16MB, 32MB, 64MB Cache: 16MB, 32MB, 64MB Interface: Interface:  IDE(PATA): Data Transmission Rate: 100MB/s, 133MB/s Data Transmission Rate: 100MB/s, 133MB/s Rotational Speed: 5400RPM, 7200RPM Rotational Speed: 5400RPM, 7200RPM  Serial ATA(SATA) : Data Transmission Rate: SATA-1(150MB/s), SATA-2(300MB/s) Data Transmission Rate: SATA-1(150MB/s), SATA-2(300MB/s) Rotational Speed: 7200RPM, 10000RPM Rotational Speed: 7200RPM, 10000RPM  SCSI(): support hot swap  SCSI(Small Computer System Interface): support hot swap Data Transmission Rate: 320MB/s Data Transmission Rate: 320MB/s Rotational Speed: 10000RPM, 15000RPM Rotational Speed: 10000RPM, 15000RPM

9. NANJING UNIVERSITY OF INFORMATION SICENCE & TECHNOLOGY  Hard Disk Cartridges Can be removed easily, so can be used for protecting sensitive information Can be removed easily, so can be used for protecting sensitive information The number of cartridges can be expanded to increase the storage capacity The number of cartridges can be expanded to increase the storage capacity Mainly used to complement the internal hard disk and provide additional capacity Mainly used to complement the internal hard disk and provide additional capacity Categories: Categories: Removable hard disks Removable hard disks PC Card hard disks PC Card hard disks

10. NANJING UNIVERSITY OF INFORMATION SICENCE & TECHNOLOGY  Hard Disk Packs Use more large platters aligned one above the other to store massive amounts of information Use more large platters aligned one above the other to store massive amounts of information The pack is mounted onto special drives The pack is mounted onto special drives The drive rotates the pack and access arm move in and out between the rotating platters. The drive rotates the pack and access arm move in and out between the rotating platters. Each access arm has two read/write heads, one reads the disk surface above it and the other read the disk surface below it. Each access arm has two read/write heads, one reads the disk surface above it and the other read the disk surface below it. All the access arms move in and out together. However, only one of the read/write head is activated at a moment. All the access arms move in and out together. However, only one of the read/write head is activated at a moment. A disk pack with 11 disks provides 20 recording surfaces, because the top and bottom outside surfaces are not used. A disk pack with 11 disks provides 20 recording surfaces, because the top and bottom outside surfaces are not used.

11. NANJING UNIVERSITY OF INFORMATION SICENCE & TECHNOLOGY  Performance Enhancement Disk caching through hard disk cache Disk caching through hard disk cache Hard disk cache acts as a temporary high-speed holding area between the hard disk and the CPU. Hard disk cache acts as a temporary high-speed holding area between the hard disk and the CPU. Frequently used data is first detected and read from the hard disk into the cache. Then the data is accessed directly from cache to CPU when needed. Frequently used data is first detected and read from the hard disk into the cache. Then the data is accessed directly from cache to CPU when needed. The performance is increased since the transfer rate from memory is much faster than from the hard disk The performance is increased since the transfer rate from memory is much faster than from the hard disk

12. NANJING UNIVERSITY OF INFORMATION SICENCE & TECHNOLOGY RAID(Redundant Array of Inexpensive Disk) RAID(Redundant Array of Inexpensive Disk) Several inexpensive hard disks are connected to one another to provide large amount of storage capacity. Several inexpensive hard disks are connected to one another to provide large amount of storage capacity. RAID technology and special RAID devices are used to connect or group the hard disks together. RAID technology and special RAID devices are used to connect or group the hard disks together. can provide large capacity, fast access speed and high reliability can provide large capacity, fast access speed and high reliability Mainly used by Servers in large companies or organizations Mainly used by Servers in large companies or organizations

13. NANJING UNIVERSITY OF INFORMATION SICENCE & TECHNOLOGY Levels RAID Level 1: Provides disk mirroring. Data written to one disk is mirrored to second disk. Level 2: Bit-interleaved data. The data is interleaved across drives. Check disks used to identify disk errors. Level 3: Bit-interleaved data with fewer check disks. Disk controller detects errors, check disk recovers data. Level 4: Interleaved data, independent reads and writes. Spreading data Transfer across disks provides higher performance. Level 5: Data and parity are spread over all disks. No check disk required. Performance and useful storage capacity improved.

14. NANJING UNIVERSITY OF INFORMATION SICENCE & TECHNOLOGY Stripe mirror Stripe+parity Stripe+mirror

15. NANJING UNIVERSITY OF INFORMATION SICENCE & TECHNOLOGY File compression and file decompression File compression and file decompression Reduce file size to save store capacity Reduce file size to save store capacity Helps to speed up transmission of files over the Internet Helps to speed up transmission of files over the Internet Redundant information, such as repeating patterns in the file can be replace by a token. Redundant information, such as repeating patterns in the file can be replace by a token. Some characteristic tokens should be kept so that the original file can be rebuilt or decompressed. Some characteristic tokens should be kept so that the original file can be rebuilt or decompressed. Popular used software: Popular used software: WinZip WinZip WinRAR WinRAR

16. NANJING UNIVERSITY OF INFORMATION SICENCE & TECHNOLOGY Optical discs Optical discs  Two Laser Beams of the optical disc drive: Read/Write  unlike the floppy disks and hard disks use the magnetic charges, optical discs use flat areas called lands and bumpy areas called pits on the disc surface to represent 1s and 0s.  Optical discs only use concentric rings called tracks to record the information  Compact Disc(CD) Popular Capacity: 640MB, 720MB Popular Capacity: 640MB, 720MB Three types Three types Read only---CD-ROM(compact disc-read only memory): can’t write and erase Read only---CD-ROM(compact disc-read only memory): can’t write and erase Write once----CD-R (CD-recordable): can write once Write once----CD-R (CD-recordable): can write once Rewritable--- CD-RW (compact disc rewritable, erasable optical discs): Rewritable--- CD-RW (compact disc rewritable, erasable optical discs): can erase and write for many times can erase and write for many times

17. NANJING UNIVERSITY OF INFORMATION SICENCE & TECHNOLOGY  DVD (digital versatile disc or digital video disc) Popular Capacity: from 4.7GB-17GB Popular Capacity: from 4.7GB-17GB DVD ROM Driver DVD ROM Driver Three types Three types Read only---DVD-ROM: can’t write and erase Read only---DVD-ROM: can’t write and erase Two categories of DVD that can be write once Two categories of DVD that can be write once  DVD+R: stands for recordable DVD proposed by Sony, Philips and HP stands for recordable DVD proposed by Sony, Philips and HP  DVD-R: stands for write once DVD proposed by Pioneer stands for write once DVD proposed by Pioneer

18. NANJING UNIVERSITY OF INFORMATION SICENCE & TECHNOLOGY Rewritable Rewritable DVD-Rewritable: DVD-Rewritable:  DVD-RW  DVD+RW DVD-Random Access Memory  DVD-RAM

19. NANJING UNIVERSITY OF INFORMATION SICENCE & TECHNOLOGY  High-definition Discs DVD have sufficient capacity to record standard-definition movies and music, but they are insufficient to record high-definition video. DVD have sufficient capacity to record standard-definition movies and music, but they are insufficient to record high-definition video. The next generation of optical disc: hi def(high-definition disc) The next generation of optical disc: hi def(high-definition disc) Two hi def discs: Two hi def discs: HD DVD(High definition DVD): HD DVD(High definition DVD): have the capacity of 15 to 45 GB have the capacity of 15 to 45 GB Blue-Ray (BDs): Blue-Ray (BDs): a different format from DVD or HD DVD which need a special Blue-Ray driver a different format from DVD or HD DVD which need a special Blue-Ray driver have the capacity of 25 to 50 GB have the capacity of 25 to 50 GB HD DVD and Blue-Ray Discs are not compatible with one another. HD DVD and Blue-Ray Discs are not compatible with one another. Which will be the next-generation standard? Who knows? Which will be the next-generation standard? Who knows?

20. NANJING UNIVERSITY OF INFORMATION SICENCE & TECHNOLOGY Other Types of Secondary Storage Other Types of Secondary Storage  Specialized storage: solid-state storage, Internet hard drives and magnetic tape  Solid-state storage: have no moving parts and needn’t special drivers and read/write heard. Flash Memory cards: Flash Memory cards: high speed, easily removable, reliable, usually used for digital cameras. high speed, easily removable, reliable, usually used for digital cameras. Usually used to store images captured from digital video cameras and then to transfer to the computers. Usually used to store images captured from digital video cameras and then to transfer to the computers. Some of the laptops have the Flash memory card port for card insertion Some of the laptops have the Flash memory card port for card insertion categories: SD card, CF card, XD card, memory stick categories: SD card, CF card, XD card, memory stick

21. NANJING UNIVERSITY OF INFORMATION SICENCE & TECHNOLOGY USB drives: USB drives: Directly connect to a computer’s USB port Directly connect to a computer’s USB port Usually have the capacities of 2GB, 4GB, 8GB, 16GB, and even 32GB and 64GB Usually have the capacities of 2GB, 4GB, 8GB, 16GB, and even 32GB and 64GB Replacing the floppy disks due to the small size and high capacities Replacing the floppy disks due to the small size and high capacities

22. NANJING UNIVERSITY OF INFORMATION SICENCE & TECHNOLOGY  Internet Hard Drives Special service sites on the Internet provide users with storages Special service sites on the Internet provide users with storages Internet hard drive Internet hard drive Advantages: Advantages: Low cost Low cost Flexibility to access information from any location using the Internet Flexibility to access information from any location using the Internet Disadvantages: Disadvantages: Access speed is slower because all information must travel across the Internet Access speed is slower because all information must travel across the Internet Security is a problem for Internet storage Security is a problem for Internet storage Unfit for storing high personalized and sensitive information Unfit for storing high personalized and sensitive information Some Internet Hard Drivers examples: iback, Xdrive and so on Some Internet Hard Drivers examples: iback, Xdrive and so on

23. NANJING UNIVERSITY OF INFORMATION SICENCE & TECHNOLOGY  Magnetic Tape Two different access approaches to external storage Two different access approaches to external storage Direct access: Direct access: Disks provide fast direct access. Disks provide fast direct access. Sequential access: Sequential access: Tapes provide slower sequential access. Tapes provide slower sequential access. Information is stored in sequence Information is stored in sequence Searching must begin from the beginning one by one, which takes time Searching must begin from the beginning one by one, which takes time Store data by altering the electromagnetic charges on the recording surface. Store data by altering the electromagnetic charges on the recording surface. Although slower to access information, it is an effective and commonly used tool for backing up data. Although slower to access information, it is an effective and commonly used tool for backing up data. Magnetic tape reels, tape cartridges or magnetic tape streamers Magnetic tape reels, tape cartridges or magnetic tape streamers

24. NANJING UNIVERSITY OF INFORMATION SICENCE & TECHNOLOGY Mass Storage Devices Mass Storage Devices  Mass storage refers to the tremendous amount of secondary storage required by large organizations  Mass storage devices are specialized high-capacity secondary storage devices used by large organizations  Enterprise storage system: Promote efficient and safe used of data across the networks within the organizations  Support the following strategy: File servers File servers Raid systems Raid systems Tape library Tape library DVD-ROM jukeboxes DVD-ROM jukeboxes Organizational Internet storage Organizational Internet storage