SECONDARY STORAGE DEVICE

 Secondary Memory:

Secondary memory refers to the permanent storage of data. It is also known as backup memory. It has higher storage capacity than the primary memory. There are various types of secondary storage devices. Some of them are:

1.Magnetic Disk:  Magnetic Disks are storage devices that are also made up of magnetic coated material. The surface of each disk is marked with invisible circular tracks. The data is stored in the form of magnetic spot on disk.

• Hard Disk: It is the most widely used internal storage magnetic disk. It is made up of spindles of smooth metallic plates coated with thin layer of magnetic material. Each plate of a hard disk is called a platter. Each platter has two (read/write) heads, one on each side. It has high storage capacity and is much faster which provides an easy access to data.
• Hard disk is also known as Winchester Disk.
• Hard Disk is invented by ‘Reynold Johnson’ at IBM in 1956.
• Seagate is the 1^st company to ship the hard disk of 8TB storage capacity.

   2.Optical Disk: Optical disks are commonly used as an external storage device in which the laser beam helps to read data from the flat surface of the optical disk.

• CD: CD or Compact Disk is a common optical disk. It is made up of light weight plastic material with a chemical coating on one side where data is stored. It is inserted into a CD/DVD Drive or CD/DVD writer of a CPU. The capacity of 120mm standard CD is 700MB.
•   DVD: DVD or Digital Versatile/Video Disk is an optical disk which looks like a CD but has a capacity to store data upto 17.1 GB.  DVD is merging of video and audio in a common format.
• Blue-ray disk: Blue ray disk can store data upto 128 GB. It has been developed by Blue Ray Disk Association (BDA). It is much advanced than CD or DVD. Blue violet laser is used to read or write data in blue ray disk.
• Diameter of a CD, DVD or Blue Ray disk is 120mm.
• DVD can also be of 80mm diameter that can hold data upto 1.5GB.
• CD can be used and played in a DVD ROM or DVD player but DVD cannot be operated in a CD player.
• A combo drive is a device which contains all the features of a CD writer and a DVD ROM.

  3.Flash Memory: Flash memory is an external  storage device that is commonly used in digital cameras and MP3 players and is smaller in size. It is connected or attached to the computer’s USB or Fire wire port.

•   PEN/Flash Drive: It is small in size, handy and is a detachable device from which data can be read, copied or transferred from one system to another. It is re-writable, portable and store more data than a CD. It weight less than 25gm. It has an attachment slot which can be easily inserted or attached into the computer’s USB port to read and write data.
•   Memory Stick: Memory stick is a detachable flash memory card device that was launched by Sony in 1998. The data stored in memory card can be read or written with a memory stick. Memory stick has a high storage capacity and provides faster speed of data transfer. Memory sticks vary in their size and capacity from 1GB to 128 GB. It is a common device widely used in digital camera and mobile phones. It is available in different names Like: MMC, SDC, Micro SD, etc.