Common types of storage - magnetic storage
Introduction
There are three main types of technology for storage. These are optical, magnetic and solid state technology.
Magnetic devices - hard drives
A typical hard drive is made up of a number of disks, also called platters, arranged on top of each other. These spin very fast, up to 10 000 times a second. A read / write head moves across each side of each disk. When you are writing to a disk, the head magnetises and demagnetises tiny areas to represent binary ones and zeros. To read from a disk, the head moves over the disk and 'reads' whether an area is magnetised or not. It collects all of this information, processes it and then uses it.
What makes a 'good' hard drive?
Each side of each disk in a hard disk is arranged into tracks, like the tracks on an old vinyl record. Each track is further split up into sectors. Every sector has a unique address. Data is stored in these sectors. The time taken for the Read / Write head to get to a particular sector is known as the seek time and is one important technical piece of information to check when buying a new hard drive - the faster the seek time, the faster you can read / write to the disk.
Another thing to look out for if you ever have to buy a new hard drive is how fast the disk spins - the faster they spin, the quicker reading and writing data can take place so the faster your computer can work.
Magnetic devices - magnetic tape
Magnetic tape is most commonly used to back-up entire networks because tapes can hold huge amounts of data. The technology is similar to hard drives in that areas are magnetised and demagnetised to write to the tape using a reading head positioned over the tape. The same head is used to read whether areas are magnetised or demagnetised, to read back data.
Serial access versus random access (also called direct access)
Unlike hard disks, the tape doesn't spin! The head is in a fixed position and the tape moves over it in a serial manner. We talk about magnetic tape being a serial access device, because to get some data back, you have to start at the beginning of the tape and work your way through it. A hard disk, on the other hand, is not serial access. You can go straight to a particular sector on a disk. We say that it is a random access device.
Advantages and disadvantages of magnetic storage devices
-
- Magnetic tape is a really good choice for data storage where huge volumes of data need to be stored, but where access times are relatively unimportant.
- Hard drives are really fast random access devices and like tape, can store large amounts of data.
- Both hard drives and magnetic tape are tried and tested storage technologies that are widely supported.
- Magnetic storage devices cost very little per megabyte.
- Hard drives have moving parts and are very sensitive; they are susceptible to damage, especially in portable devices like laptops which get frequent knocks.
- Data on a hard drive or tape can be corrupted if it gets too close to a source of magnetism.
- Compared to solid state devices, the data access speeds are slow. Another way to dramatically improve a computer's performance (especially an old computer) is to swap the magnetic hard drive for a solid state one.