2. MEANING OF SECONDARY STORAGE Secondary storage of the computer’s memory is non-volatile and has lower cost per bit stored,but it generally has an operating speed far slower than that of the primary storage.This section of the memory is used to store large volume of data on a permanent basis,which can be partially transferred to the primary stage, as and when required for processing.
5. MAGNETIC TAPE: It is the most popular storage medium for large data,which are sequentially accessed and processed.the magnetic tape medium is a plastic ribbon,which is usually ½ inch or ¼ inch wide, and 50 to 2400 feet long.It is coated with a magnetizable recording material, such as iron oxide or chromium dioxide.Data are recorded on the tape in the form of any tiny invisible magnetized spots on the coated surface of the tape.The tape ribbon is itself stored in reels or a small cartridge or cassette.
6. TYPES OF MAGNETIC TAPE : 1. 1/2-inch tape reel 2. 1/2-inch tape cartridge 3. 1/4-inch streamer tape 4. 4-mm digital audio tape(DAT)
7. ADVANTAGES OF MAGNETIC TAPE Their storage capacity is virtually unlimited, because as many tapes, as required ,can be used for strong very large data sets. With the low cost of tape reels and cartridges, and high data recording densities , the cost per bit of second is very low for magnetic tapes.It can also be erased and reused many times. The tape reels and cartridge are compact and light weight,they are easy to handle and store.very large amount of data can be stored in a small storage space.
8. LIMITATIONS OF MAGNETIC TAPE They must be stored in a dust-free environment, because specks of dust can cause tape-reading errors. They must also be stored in an environment with properly controlled temperature and humidity levels otherwise, the tape ribbon may get twisted due to warping, resulting in loss of stored data. They must be properly labeled, so that some useful data stored on a tape is not erased by mistake.
9. Transferring of data and program from one computer to another,which are not linked together. Archiving of data which are not used frequently, but which may be used once in a while. Backing up of data stored on an on-line storage device,such as a disk,for its off-line storage. USES OF MAGNETIC TAPES
10. MEANING OF DIRECT ACCESS STORAGE In many applications, we need to access information in a more direct manner than sequential-access devices allow.For example, in a computerized bank at any instance it is required to determine the exact balance in the savings account of a particular customer.These direct access devices are also called random-access devices, because the information is literally available at random, i.e.it is available in any order.Hence, a random-access storage is one in which any location in the device may be selected at random, access to the information stored is direct, and approximately euqal access time is required for each location.Magnetic and Optical disk are examples of direct access storage devices.
11. 1. MAGNETIC DISK: Magnetic disk is the most popular storage medium for direct access secondary storge.Due to their random access capability,magnetic disks are the most popular on-line secondary storage device.A magnetic disk is thin, circular plate/platter made of metal or plastic,which is usually coated on both sides with a magnetizable recording material such as iron oxide. Data are recorded on the disk in the form of tiny invisible magnetized and non-magnetized spots on the coated surfaces of the disk.
12. ADVANTAGES OF MAGNETIC DISK Magnetic disks are suitable for both on-line and off-line storage of data. Due to their low cost and high data recording densities, the cost per bit of storage is low for magnetic disks. Magnetic disk are often used simultaneously by multiple user as a shared device.
13. LIMITATION OF MAGNETIC DISK It is more difficult to maintain the security of information stored on magnetic disk. They must be stored in a dust free environment. Some type of magnetic disks,such as disk packs and winchester disks, are not so easily portable like magnetic tapes.
14. USES OF MAGNETIC DISKS For application that are based on random data processing. Transferring of data and programs from one computer to another, which are not linked together. Distribution of software by vendors. As a shared, on line secondary storage device.
15. 2. OPTICAL DISK: An optical disk storage system consist of a rotating disk, which is coated with a thin metal or some other material that is highly reflective.Laser beam technology is used for recording/reading of data on the disk.Due to the use of laser beam technology, optical disk are also known as Laser disks or optical laser disks. As compared to magnetic tape and magnetic disk,optical disk is a new secondary storge medium.
16. ADVANTAGES OF OPTICAL DISKS The cost per bit of storage for optical disk is very low, because of their low cost and enormous storage density. The use of a single spiral track makes optical disks an ideal storage medium for reading large blocks of sequential data,such as music. Due to their compact size and light weight, optical disk are easy to handle,store,and port from one place to another.
17. LIMITATIONS OF OPTICAL DISKS It is a read-only (permanent) storage medium.Data once recorded,cannot be erased, and hence, the optical disks cannot be reused. The data access speed for optical disks is slower than magnetic disks. Optical disks require a more complicated drive mechanism than magnetic disks.
18. USES OF OPTICAL DISKS For distribution of electronic version of conference proceedings,journals,magazines etc. For distributions of new or upgraded versions of software products by software vendors. For storage and distribution of a wide variety of multimedia applications, such as video games. For archiving of data, which are not used frequently, but which may be used once in a while.
