Revising concepts

1. The primary storage devices are used to store information only when the computer is on. 
2. Secondary storage devices were developed to store data and information permanently on them.
3. The different units of memory are bits, bytes, kilobytes, megabytes, gigabytes and terabytes.
4. The floppy disks are simplest and most popular secondary storage device. 
5. The commonly used floppy disks are of 3.5" diameter and 1.44MB storage capacity.
6. Hard disks are the secondary storage device installed inside the CPU of the computer. 
7. The speed of harddisks is 3600 revolutions per second and the storage capacity of the hard disks ranges from 10 GB to 40GB.
8. Compact discs commonly called CDs are used to store 60MB to 750MB of data. The CDs are also available as audio CDs to listen music and video CDs to watch movies.
9. The diameter of the CD ranges from 10 cms to 30 cms. A typical CD is of 13 cm diameter. 
10. One CD can store 600 MB to 750 MB data on it.
11. Laser reads the normally used CDs.
12. CD comprises of a transparent thin layer of aluminium covering the pitted surface for reflectivity