Magnetic storage media depend on the magnetic properties of certain materials (iron and nickel alloys being the most common). Magnetic material is coated on the surface of a disk or tape that can be magnetized in such a way as to represent a l or a 0. Many hard disk drives are made up of more than one disk and these disks are known as platters. Each platter is made from glass, ceramic or aluminum coated in a nickel alloy that can be magnetized. In the case of tape, plastic that is coated in a magnetic material is used to store the data.
Fixed/internal hard disk drive (HDD)
Fixed hard disk drives are available on all computers and are the main method used for data storage. On a PC this is usually a fixed hard disk with read/write heads allowing data to be written to or read from the disk surface. The disk surface is coated in a magnetic film that allows data to be stored by altering the magnetic properties to represent binary Is or Os (the fundamental units of computer memories). The hard disks usually store the disk operating system (DOS) and other systems software, as well as applications software and files.
Applications software (such as spreadsheets and word processors) also needs a hard drive to allow them to quickly retrieve and save data.
Uses
• To store the operating system, systems software and working data/files.
• Storing applications software that needs fast retrieval and storage of data.
• ,Used in real-time systems (tor example, robots, control of a chemical plant. where data for the process is stored to allow real-time operations) and in online systems (for example, booking airline tickets or automatic stock control using EFTPOS, which allows immediate updating of the stock files).
• Used in file servers for computer networks.
Advantages
• They have a very fast data transfer rate and fast access times to data.
• They have very large memory capacities.
Disadvantages
• Can be easily damaged if the correct shut down procedure is not carried out; this can lead to a head crash which would result in a loss of data.
• They have many moving parts when compared to, for example solid state drives (SSDs).
• Their read/write operation can be quite noisy compared to SSDs.
These devices work in much the same way as fixed hard disk drives but are usually connected to the computer via the USB (universal serial bus) port and can be disconnected and used on different computers. The disks are generally capable of storing more data than the equivalent optical disk (CD, DVD and so on).
Uses
• They can be used as backup systems to prevent loss of data.
• They can be used to transfer data/files/software between Computers.
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.
Disadvantages
• They can be easily damaged if drop pad or subjected to a strong magnetic field; as with fixed hard disk drives, an incorrect shut-down procedure could also lead to loss of data.
Magnetic tapes
A magnetic tape is a very thin strip of plastic that has been coated in a magnetic layer. They are read and written to by a read/write head. The data is stored in magnetic areas that represent Is and 0s. Data is read from the tape using serial access (see earlier description). This type of storage is useless in real-time or online applications (due to the very slow data access speeds) and is best suited to offline or batch processing.
Uses
• In applications where batch processing is used, for example, clearing bank cheques, utility billing (gas, electricity, water) and producing pay slips; in these applications there is no need for any specific processing order and speed of data access is not essential.
• Used as a backup media since all the data needs to be stored.
• Used in long-term archiving of data; magnetic tapes have huge data storage capacities and are known to be very stable, which makes them ideal for long-term storage.
Advantages
• They are generally less expensive (per byte) than the equivalent hard disk.
• It is a very robust technology (they don't deteriorate very much over time).
• They have a huge data storage capacity.
• The data transfer rate is actually fast (this should nor be confused with data access time, which is very slow for magnetic tapes).
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 needed to store the final updated version.
• They are affected by magnetic fields; a strong magnet can corrupt data stored on the tape.
