Storage

Storage

1. Primary memory

   • RAM and ROM

2. Secondary storage

   • why back up data?
     • 1. to safeguard against loss of data due to the failure of the original secondary storge device
     • 2.to safeguard against damage caused by hackers
     • 3.backups are also made in case the files need to be used elsewhere
     • 4.backups don't necessarily guard against the effect of a virus

3. Backing up

   • copying of files/data to a different medium (disk, tape, flash drive, etc)
   • In case of a problem with the main secondary storage device.

4. Types of access

   • three terms
     • field
     • file.
     • record
   • serial access
     • The transaction file contains all the new data to allow the master file to be updated.
   • direct access
     • The computer uses the key filed to caculated position
     • Access is much faster than with serial access

5. Secondary storage media

   • measurement of storge
     • byte
     • kilobytes(kB)
     • megabytes(MB)
     • gigabytes(GB)
     • terabytes(TB)

6. Magnetic storage

   • fixed/internal hard disk drive(HDD)
     • Disadvantage
       • can be easily damaged it
       • they have many moving parts when compare to(eg solid state drive SSD)
       • their read/write operation can be quite noisy compare to SSDs
     • Advantages
       • they have a very fast data transfer rate and fast access times to data
       • they have very large memory capacities
   • Portable hard disk drives
     • Disadvantages
       • they can be easily damaged if dropped or subjected to a strong magnetic field
     • Advantages
       • the data access time and data transfer rate is very fast
       • they have a large memory capacity
       • they can be used as a method of transferring information between computers.
   • Magnetic tapes
     • Advantages
       • They have a huge data storage capacity.
       • The data transfer rate is actually fast.
       • They are generally less expensive than equivalent hard disk
       • It is a very robust technology
     • Disadvantages
       • Very slow data access times(need to read all the earlier records on the tape until the required record is found).
       • When updating, another tape is need to store the final updated version
       • They are affected by magnetic fields

7. Optical storage media

   • CD-ROM and DVD-ROM
     • Advantages
       • They hold far more data than floppy disks
       • They are less expensive than hard disk drive systems
     • Disavantages
       • They data transfer rate/data access time is slower than for hard disks.
   • R-write once only ROM-can only be read RW-can be written to or read for many times
   • CD-R and DVD-R
     • Disavantages
       • If finalised, the CD-R/DVD-R can only be recorded on once
       • Not all CD/DVD players can read CD-R/DVD-R
     • Advantages
       • Cheaper than RW disks
       • Once burned (like a ROM)
   • CD-RW and DVD-RW
     • Disavantages
       • Can be relatively expensive
       • It is possible to accidentally overwrite data
     • Advantages
       • Can be written over mant times
       • Can use different file formats each time it is used
   • DVD-RAM
     • Disadvantages
       • Many systems won't recognise the DVD-RAM format.
       • Relatively expensive
       • They have been superseded by newer technologies such as solid state memories
     • Advantages
       • It is possible to da a rewrite operation over 100000 times
       • They offer the ability to read data at the same time as data is being written
       • Very fast access if the files are fairly small
       • Reliable-they have in-built verification software ,accuracy of the data is ensured
       • They have a long life
       • Very large capacity
       • No need to finalise the disk
   • Blu-ray discs
     • Advantages
       • The data access speed is also greater than with other optical media
       • Very fast data transfer rate
       • Blu-ray discs automatically come with a secure encryption system, which helps to prevent piracy and copyright infringement
       • Very large storage capacity(storing high-definition moves)
     • Disavantages
       • Relatively expensive
       • Encryption problems when used to store video
       • There are fewer movie titles on Blu-ray format, which is reducing its impact on the home movie market.
   • The future of optical media
     • Many computer systems bow come with USB connectors only and no DVD or CD drive.

8. Solid state storage media

   • Solid state deives(SSD)
     • Disadvantages
       • Most SSD devices are conservatively rated at only 20GB write operations per day over a three-year period
     • Advantages
       • They are more reliable
       • They are considerably lighter(suitable for laptops)
       • They don't have to get 'up to speed' before they work properly.
       • They have a lower power consumption.
       • They run much cooler than HDDs(very suitable for laptops)
       • Because there are no moving parts, they are very thin
       • Data access is considerably faster than HDD.
   • Flash memory cards
     • Disavantages
       • Expensive oer gigabyte of memory when compare to HDDs
       • Have a lower storage capacity than hard disks
       • Have a finite life regarding the number of times they can be read from or written to.
     • Advantages
       • Very compact and can be easily removed and used un another device or for transferring photos directly to a computer or printers.
       • Since they are solid state mrmories, they are very robust.
   • Memory sticks/pen drives
     • Advantages
       • Very compact and portable media
       • Very robust
       • Doesn't need additional software to work on most computers.
     • Disadvantages
       • Can't write-protect the data/file
       • Easy to lose
       • The user needs to be very careful when removing a memory stivk from a computer-incorrect removal

Images and files in the map