Secondary Memory:
Secondary memory is permanent memory. It is not directly accessible by CPU. It communicates with the CPU through the main memory. Secondary memory stores data and holds it even when power is off. It is used to store large amount of data or programs. It is less expensive than the primary memory.
Secondary memory refers to the various storage media on which a computer can store data and programs. Floppy disks, Hard Disks, magnetic disks, magnetic tapes are the examples of secondary memory.
The Secondary storage media are of two types:
- Fixed: Fixed Storage media is an internal storage medium like hard disk that is fixed inside the computer.
- Removable: Storage medium that are portable and can be taken outside the computer are termed as removable storage media like CD, DVD, Pen drive etc.
Characteristics of Secondary Memory:
- These are magnetic and optical memories.
- It is known as the backup memory.
- It is a non-volatile memory.
- Data is permanently stored even if power is switched off.
- It is used for storage of data in a computer.
- Computer may run without the secondary memory.
- Slower than primary memories.
(i) Magnetic Tapes:
Magnetic discs are made of hard metal or synthetic plastic material. Magnetic material is coated on both sides of the disc platter and both sides can be used for storage. The magnetic disk provides direct access to both small and large computer systems. Magnetic audio tapes are used to record sound and music. Magnetic video tapes are used to record analog voice and video signals. These are low cost tapes. Hard disks and floppy disks are examples of magnetic tapes.
(ii) Floppy Disk:
Also known as floppy diskette, it is a removable, portable secondary storage device. This was created in 1964 by IBM. It is a small plastic disc about 3.5 inches in size. These disks have very low storage capacity and can store approximately 1.4 MB of data. It can be read or written by a floppy disk drive.
(iii) Hard Disk:
Hard disks are the secondary storage devices used to store data permanently. It is directly connected to the disk controller on the motherboard. Hard disks are flat, circular plates made of aluminum or glass and coated with a magnetic material. Hard disk platters typically spin very fast at 5400 to 7200 cycles/minute.
It has unlimited storage space and its storage capacity ranges from 20 GB to 500 GB. It used to install a new program or application on the device. Software programs, images, videos, etc. all can be saved to the hard drive.
There are two types of hard disks.
1. Internal Hard Disk: Internal hard drives are located inside your computer. Most computers come with a single internal hard drive, which includes the operating system and pre-installed applications.
2. External Hard Drive:
An external hard drive, also called a portable hard drive. It is a device connected to the outside of a computer via a USB connection. It is often used to back up a computer or portable storage.
(iv) Optical Drives:
Optical drives are a storage medium from which data is read and written by a laser. Optical disks can store up to 6 GB of data. Optical storage devices are the most widely used and reliable storage devices.
The most commonly used types of optical storage devices are:
- CD-ROM
- DVD-ROM
- CD-RECORDABLE
- CD-REWRITABLE
- PHOTO-CD
1. CD:
A compact disc is a flat, round, optical storage medium invented by James Russell. It is a portable storage medium that was used to digitally store and play the audio, video and other data. Compact discs have greater storage capacity than floppy disks. These disks can store 650-700 MB of data. This is a very reliable storage media. There are two types of CDs :
(а) CD-R:
CD-R stands for Compact Disc-Recordabie, also known as ROM is a digital optical disk storage format. A CD-R disc is a compact disc that can be written once and arbitrarily read multiple times.
(b) CD-RW:
CD-RW (compact disc-rewritable) is a digital optical disk storage format introduced in 1997. A CD-RW compact disc (CD-RW) can be read, written, erased, and rewritten.
2. DVD:
Stands for Digital Video Disc or Digital Versatile Disc. It is a digital optical disc data storage format that was invented and developed in 1995 and released in late 1996. DVD is a type of optical media used to store digital data. It is the same size of a CD, but it has a large storage capacity. Some DVDs are specifically formatted for video playback, while others contain different types of data, such as software programs and computer files.
While using CDs and DVDs, we should keep the following in mind:
- CD / DVD should always be covered.
- The back shiny part of the CD / DVD should not be touched.
- Don’t write on the back of the CD / DVD.
- CD / DVD should not be folded.
- To clean CDs / DVDs / DVDs, a soft cloth should be used. You can also use water to remove dust from it.
3. Pen Drive:
A pen drive is a portable universal serial bus (USB) flash memory device. It is used to store and transfer audio, video and data files from a computer. The major advantage of USB pen drives over other portable storage devices such as floppy disks or DVDs / CDs is their compact shape and size; they work faster and can store more data.
4. Memory Card:
A memory card is a flash memory. It is used in electronic devices such as digital cameras, Mobile phones or video game consoles. The memory card can stores data, images, music, games or other computer files. Memory cards have no moving parts so they are not easily damaged. They are more compact and portable than CDs or DVDs, and they can store more data than CDs. The data stored in the memory card can be read with the help of card reader.
