Hard Disk
The computer may also have a hard disk houses inside the computer's cabinet. Hard disks are similar to floppy disks except that they are rigid. They also have larger storage capacities and can be written and read more quickly by the computer. Programs can be copied into the hard disk from floppy disk. So, this is a convenient way of putting new programs onto a computer. Once the hard disk the program can be read more quickly and easily.
The device into which a disk fits is called a disk drive. Most PCs have a combination of hard disk drive and floppy disk drive. If there are multiple disk drives they are often labelled 'A', 'B', 'C', e.t.c. The storage capacity of hard disk in micros ranges from 10MB to several gigabytes.
Advantages of Disk Storage Devices
As in the case of magnetic tape, once data have been recorded on a magnetic disk, they may be read in an indefinite number of times and will remain on disk until they are written over. Disk Storage Devices are capable of reading and writing data sequentially or directly, which makes them very flexible.
Disk packs also provide the capacity of easy removal and portability. A disk storage facility contains multiple disk units and can provide direct access storage in gigabytes, access any record stored in an average time of a few thousandths of a second, and transfer information between it and the CPU at a rate more than 2million bytes per second.
Magnetic Bubble Storage
Bubble memory consists of a thin magnetic film in which cylindrical magnetic fields or 'bubbles', are generated. The bubbles are carrying with them opposite polarity (i.e. magnetic north instead of south or vice versa) to the thin film of magnetic crystal line material that contains them.
A magnetic field moves the bubbles around the chip, but the bubbles are microscopic and stay within the magnetic film. Bubble memory is non-volatile, and so data is not lost when power is turned off.
Storage capacities are quite high. It's performance is unaffected by dirt, humidity and wide changes in temperature. It has high level of immunity to radio and electromagnetic interference.
However, bubble memory is expensive and not a challenge to disk-based backing store in the home or office. But in military and space application, and also in some industrial contexts, the ruggedness of bubble memory is essential.
Optical Disks
Although a relatively new entrant into the microcomputer secondary storage arena, optical Disks have been used for music videos and audio recording for some time. The optical disk used with computers is similar to the magnetic disk in that data is recorded in sectors within tracks, but it is different in the method used to record the data.
Writing is accomplished by momentarily directing a laser beam onto the surface of the disk! Optical systems are available that allow the user to write data once and read it many times. These systems are called WORM (Write Once Read Many) systems. CD-ROM (Compact Disk — Read Only Memory) Systems are also available that can only read pre-recorded disks.
Also Erasable Optical Disks are available: these combine optical and magnetic technologies, such that you can read and write to the disk. These systems are practical for large universally used common databases (document and images), education, reference and home entertainment; e.g. a multi-volume encyclopedia can be held on one CD.
What makes optical disk an attractive storage medium is that the life expectancy of data stored optically is approximately three times the shelf life of magnetically recorded information. These optical media have an enormous storage capacity, ten to thirty times than that of magnetic media.
In terms of cost effectiveness, the optical disk is ideal for storing large volumes of relatively permanent data. However, one big disadvantage with the CD-ROM and WORM is that once data has been burnt onto the disk, it is there forever.
Conclusion
Storage Devices are very essential in our computer system. It has many special components that enables us to write data onto the disk. A known example being the Hard Disk is a secondary storage device. However, this hard disk also stores instructions that enables our system to boot successfully!