Secondary Storage devices

Secondary Storage devices

1. Magnetic Media

   • Hard Disk
     • developed by IBM in the 50s
     • thin circular platter made of non-ferrous metal or plastic, read-write head
     • rotate up to 10,000x/min
     • platter is coated with iron of cobalt oxide particles = tiny magnets
     • magnetic particles are signed as 0 or 1 and binary is encoded
     • concentic rings called TRACKS which are divided up into SECTORS
     • both sides of the disk are used and multiples disks can run in parallel
     • address: surface(0/1), track(0-7000), sector(0-63)
   • Magnetic Tape
     • plastic tape coated on one sidewith a magnetic oxide
     • tape recorders
     • more reliable than paper tape systems
     • magnetised to record bit patterns
     • 10GB-800GB
     • 20KB of data per second - 20MB/s
     • serial; can only be written or read in the order they were written
     • early versions were open reels, sealed cartridges are more popular

2. Optical Media

   • Blu-ray
     • blue-violet laser for read/write
     • high density of tracks
     • 25GB single sided; 50GB dual sided
     • high data transfer speeds
     • supported by numerous hollywood films
   • HD DVD
     • 30GB
     • used to rival blu-ray
     • recent demise
   • Compact Disks
     • CD-ROM
       • CD read-only memory
       • used as software storage for distribution
       • 600-700MB
       • 3.5 miles of pits are impressed onto a spiral track
       • 200-500 revolutions/min
     • CD-R
       • written once, read many (WORM)
       • 120mm disks are etched with high power lasers
       • low power lasers read disk
       • 600-700MB
       • chemical reactions between gold film and bye creates less reflective areas
     • CD-RW/CD-E
       • true read/write disks
       • magnet and a laser
         • laser = read
         • magnet + laser = write
           • leaser heats to 200*C
           • magnet sets data
           • data is fixed as disk cools
       • datant is unaffected by external magnets
     • digitally encoded
   • Digital Versatile Disk
     • DVD-ROM
       • read only memory
     • DVD-RW
       • true read/write
       • often used to back up home recordings
       • faulty data can be erased
       • organic dye or phase metal can be used
     • DVD-R
       • WORM format
       • layer of dye is burnt into when writing
       • 4.7GB
       • used for archives
     • DVD-RAM
       • built in error control
       • best DVD format
       • easily written to and erased
       • concentric tracks compared to spiral track
       • 2.58-9.4GB
     • better storage capacity than CDs
     • /Digital Video Disk
     • more tracks in same space
     • shorter wave length laser beam

3. Solid-state Memory

   • USB Flash Drive
     • flash drive + UBS interface
     • small, light, cheap
     • better than floppy disks: robust, reliable, compact, data dense (12xfloppy disk)
     • Small circuit board,plastic or metal casing, USB connector, NAND memory chip
     • 63MB-32GB
     • flash memory is replacing magnetic hard disk memory in some laptops
     • Universal Serial Bus: allows periferals to be connected by a standard interface socket
   • Memory Card
     • used for data storage in digital cameras, telephones, computers, music players and games consoles
   • Type of EEPROM which can be erasued in blocks
   • To make a change, memory is copied to a buffer then erases the block and writes the altered data
   • includes a microprocessor and RAM buffer
   • can function as a music codec to turn a flash drive into an MP3