1. Unit 3

2. DATA Backing up Is the copying of files/data to a different medium (if there is a problem with the main secondary storage devices) Are often stored in a different place I case there is a fire or some other situation that could lead to loss of key data/files. For what purpose? Safety if the original file/data is lost Safety against damage caused by hackers Protects the original against possible corruption or loss

3. Types of access field= where the data are stored record= information about only one data file= all the data put together

4. Serial access Serial access is where data records are stored one after the other with no regard to the order. This is usually an unprocessed file. When using it, it is necessary to start at the beginning of the file and then access each record in turn until the required record if found. Used on magnetic tape systems and it is a very slow form of data access. When the original magnetic tape (master file) needs updating, an additional tape (transaction file) is required. Transaction file contains all the new data that allow the master file to be updated. Key field= field used to sort the records Master file=(MF) Transaction file= (TF) ISBN= Key field

5. Direct access Direct access is used with magnetic disks, optical media and solid state media. The computer uses the key field to calculate where the data should be stored. Then it is able to access the data directly. When updating takes place, the old data/records are written over. Used where data access speed is vital

6. Magnetic storage media

7. HDD= fixed/internal hard disk drive  In a personal computer, a hard disk drive (HDD) is the mechanism that controls the positioning, reading, and writing of the hard disk, which furnishes the largest amount of data storage for the PC USES  Store the operating system, system software and working data/files  Used in real-time systems(robots, control of chemical plant,..)  Used in file severs for computer networks Advantage  Fast data transfer rate & fast access times to data  Large memory capacities Disadvantage  Easily damaged  noisy

8. Portable hard disk drives  A magnetic disk drive that plugs into a USB, FireWire or eSATA port on a computer. Used for backup, secondary storage as well as transport, portable hard drives rival the capacity of many internal hard drives. USES  Used as backup systems to prevent loss of data  Used to transfer data/files/software between computers ADVANTAGE  Fast  Large memory capacity DISADVANTAGE  Easily damaged

9. Magnetic tapes  is a system for storing digital information on magnetic tape using digital recording USES  Applicatioons where batch processing is used  As backup media  Long-term archiving of data ADVANATGE  Less expensive  Robust technology  Huge data storage capacity  Data transfer rate is fast DiSADVANTAGE  Slow  When updating, another tape is needed  Affected by magnetic fields

10. Optical storage media

11. CD/DVD disk  Optical storage device. Laser ight is used to read the data. Both use a thin layer of metal. Data is stored in `pits` and `bumps` on the spiral track. Red laser is used to read and write data. Designated by:  R-write once only  ROM- can only be read  RW- can be written to or read from many times  CDs and DVDs are similar in composition and usage, however DVDs offer more data storage capacity compared to CDs. CDs are also commonly used for audio and program files, while DVDs are used for video and program files.

12. CD-rom and dvd-rom CD-ROM  Used to store music files, software, computer games,… ADVANTAGE  Hold more data than floppy disk  Less expenisve DISADVANTAGE  Slow to transfer data DVD-ROM  Store films,computer data,…

13. CD-R and DVD-R  DVD-R is a digital optical disc storage format. A DVD-R is a DVD that can be written once and read arbitrarily many times  CD-R (Compact Disc-Recordable) is a digital optical disc storage format. A CD-R disc is a compact disc that can be written once and read arbitrarily many times. USES  Home recording of music ADVANTAGE  Cheaper than RW-disks  Once burned they are like a ROM DISADVANTAGE  Can only be recorded on once  Not all CD/DVD players can read them

14. CD-rw and dvd-rw  A DVD-RW disc is a rewritable optical disc with equal storage capacity to a DVD-R  CD-RW (Compact Disc-ReWritable) is a digital optical disc storage format. A CD-RW disc is a compact disc that can be written, read arbitrarily many times, erased and written again USES  Record television programms  Not as wasteful as R format  Used in CCTV systems ADVANTAGE  Can be written over many times  Can use different file formats DISADVANTAGE  Expensive  Possible to overwrite data

15. Dvd-ram  DVD-RAM is a DVD (optical disc) technology for high-capacity data storage for computers. Like ordinary random access memory (RAM), it can be repeatedly read, written to, and erased. Intended mostly for removable computer storage, DVD-RAM provides the capabilities of Rewriteable CD (CD-RW) - users can run programs from the discs, copy files to them and rewrite or delete them. USES  Recording devies, such as satellite receivers  Camcorders, to store movies ADVANTAGE  Long life  Rewrite over 100000 times  Reliable  Fast  No need to finalise  Large capacity DISADVANTAGE  Not as compatible as R- and RW-format  Expensive

16. Blu-ray discs  Blu-ray or Blu-ray Disc (BD, BRD) is a digital optical disc data storage format. It was designed to supersede the DVD format, in that it is capable of storing high-definition video resolution (1080p)  Uses blue lasers rather than red lasers USES  Home video consoles  Storing and playing back movies  Useful for PC storage  Camcorders use media to store movie footage ADVANTAGE  Large storage capacity  Fast data transfer  Automatically come with a secure encryption system,which helps to prevent piracy and copyright infringement DISADVANTAGE  Expensive

17. Solid state storage media

18. Solid state drives (SSD)  A solid-state drive (SSD) (also known as a solid-state disk, though it contains no actual disk, nor a drive motor to spin a disk) is a solid-state storage device that uses integrated circuit assemblies as memory to store data persistently. Some solid state storage devices use EEPROM.  Electronically erasable programmable read-only memory (EEPROM), is a type of non- volatile memory used in computers and other electronic devices to store small amounts of data that must be saved when power is removed o More reliable o Considerable lighter o Lower power consumption o Run much cooler than HDDs o No moving parts, so very thin

19. Memory sticks/pen drives  Store several gigabytes of data and use solid state technology. Usually connected to a computer through the usb port and power. Extremely small and very portable. USES  Transporting files betweeen computers  Used as a security device to prevent softwarepiracy ADVANTAGE  Compact and portable media  Robust  Not affected by magnetic fields DISADVANTAGE  Can not write-protect the data  Easy to lose  User needs to be careful

20. Flash memory cards  Form of EEPROM and example of solid state memories USES  Storing photos on digital cameras  Used as mobile phone memory cards  Used in MP3 players to store music files  Used as backup store in hand-held computer devices ADVANTAGE  Compact  Very robust DISADVANTAGE  Expensive per gigabyte  Finite life  Lower storage capacity