SECONDAR Y STORAGE DEVICES The storage devices are broadly classified into Secondary storage and primary storage. The secondary storage is known as peripheral storage, and is used to stores information of the computer that is not in current use. The secondary storage is typically slower and is of higher capacity than primary storage. The secondary storage is almost nonvolatile. The secondary storage is slow due to serial access. The Primary storage is used to refer for local random access disk storage and is properly called secondary storage. If this type of storage is called primary storage, then the term secondary storage would refer to offline. This usually occurs in the slower, larger forms of storage which is used to develop the vendors to provide secure device management services, authentication services, as well as encryption for data. There is software and application based solutions; however softwarebased encryption solutions can impact performance during the storage process. Vendors provide hardware based solutions, which are appliances that provide authentication to protect the data. These devices are taken into account for the different requirements of securing data on primary or secondary storage. The primary storage performance and access specifications for the tape environment and requires the encrypting to tape would require integration with backup schemas for primary storage scenarios. NeoScale research indicated that users looking to encrypt data onto tape had lower price and different deployment requirements. These factors drove NeoScale to provide two product offerings to address the needs of each storage environment. The secondary storage helps in securing the data on media types and storage categories, as data is vulnerable to network attacks, administrative access and media theft. There are many organizations who are working with third parties and disaster recovery efforts. Often data goes offsite and is in the
hands of employees that are not authorized to see critical company data. And storage consolidation opens the door to greater administrative access. All of these trends drive the need to ensure the data at rest is secure. However, the nature of the data located on primary storage certain specifications for encryption appliances. First, let’s look at data located on primary storage arrays. Primary data is critical to the operation of the organization on a daily basis. Primary storage often contains current financial, customer, design, process or transactional information. The data must be highly available and access should be immediate, with minimal latency, particularly in transactional database environments. Many applications do not work effectively if there is excessive latency in the data path. An encryption appliance for primary storage would need to address all of these issues. Performance would be critical; the appliance cannot introduce any latency into the data path. The appliance itself would also need to be extremely secure and transparent to the network , providing levels of authentication for access to the device itself. Unauthorized users should not be able to access the encryption keys or change the configuration of the device, including policies and administration permissions. Thus, both the primary and secondary storage plays the vital part in maintaining the system storage. 1. HARD DISK : The hard disk is the basic storage device that is used in any computer system. The hard disk drive is the heart of the computer where all the information is stored. There are as usual two types of memories, one is the primary memory and the other is the secondary memory. The hard disk drive is the example of secondary memory device. The hard disk drives are available these days in many configurations such as apart from speed, the users are also looking for the access speed. That is the how fast the data can be accessed from the hard disk drive. Let us consider the basic structure of the hard disk drive. The structure of any storage media
is as much similar to that of the floppy diskette. But the major difference between the hard disk drive and the floppy disk is that the hard disk has more than just more than two sides. It is also much faster than any floppy disk. The recording media that are used for the floppy disks are the soft and hence they are called as the floppy disk. Where as the hard disk drives uses the hard surface recording media that are called as the platters. These platters are placed one above the other. The platters are where the data or the user information is stored. There are many platters over the hard disk drive. Physically the platters in the hard disk utilize the two sides also. The number of the platters is dependent over the capacity of the hard disk. The hard disks that were available earlier had considerably low memory as compared to the hard disk drives that are presently available. Hard disk drives that are available now have the memory ranging from the 40 giga bytes to that in tera bytes. One tera byte is as equal to that of 1000 of giga bytes. Each of the side of the platter of the hard disk drive has a read write head that is used for retrieval or the storage of the data over the hard disk. Each disk surface is coated with some sort of the magnetic material. This magnetic media and the read write head stores the data over it by rearranging the magnetic field. It reads the data from the surface by interpreting the variations in the magnetic field. The platters are mounted on a fixed spindle which rotates at the speed of about 5600 rpm – revolutions per minute (this is the speed of the hard disk that further categorizes it. The read write head moves horizontally across the platters from the edge to the center so that they can read or write data to any part of the surface. All the heads are assembled with an actuator, the movement of which is controlled by the stepper motor called the head stepper motor. A stopper is provided for the indication of the track 0 when the head moves towards the outermost track.
A series of the concentric circles on each platter are what known as the tracks. The division of the tracks into the smaller units is called as the sectors. The collection of the tracks that can be accessed without moving the head is called as the cylinder. . 2. Magnetic Tape : Magnetic tapes are used for large computers like mainframe computers where large volume of data is stored for a longer time. In PC also you can use tapes in the form of cassettes. The cost of storing data in tapes is inexpensive. Tapes consist of magnetic materials that store data permanently. It can be 12.5 mm to 25 mm wide plastic filmtype and 500 meter to 1200 meter long which is coated with magnetic material. The deck is connected to the central processor and information is fed into or read from the tape through the processor. It similar to cassette tape recorder.
Fig. 2.3 Magnetic Tape Advantages of Magnetic Tape: • Compact: A 10inch diameter reel of tape is 2400 feet long and is able to hold 800, 1600 or 6250 characters in each inch of its length. The maximum capacity of such tape is 180 million characters. Thus data are stored much more compactly on tape. • Economical: The cost of storing characters is very less as compared to other storage devices. • Fast: Copying of data is easier and fast. • Long ter m Storage and Reusability: Magnetic tapes can be used for long term storage and a tape can be used repeatedly with out
loss of data. 3. Magnetic Disk : You might have seen the gramophone record, which is circular like a disk and coated with magnetic material. Magnetic disks used in computer are made on the same principle. It rotates with very high speed inside the computer drive. Data is stored on both the surface of the disk. Magnetic disks are most popular for direct access storage device. Each disk consists of a number of invisible concentric circles called tracks. Information is recorded on tracks of a disk surface in the form of tiny magnetic spots. The presence of a magnetic spot represents one bit and its absence represents zero bit. The information stored in a disk can be read many times without affecting the stored data. So the reading operation is nondestructive. But if you want to write a new data, then the existing data is erased from the disk and new data is recorded. 4. Floppy Disk : It is similar to magnetic disk discussed above. They are 5.25 inch or 3.5 inch in diameter. They come in single or double density and recorded on one or both surface of the diskette. The capacity of a 5.25inch floppy is 1.2 mega bytes whereas for 3.5 inch floppy it is 1.44 mega bytes. It is cheaper than any other storage devices and is portable. The floppy is a low cost device particularly suitable for personal computer system.
Fig. 2.5 Floppy Disk
5. Optical Disk : With every new application and software there is greater demand for memory capacity. It is the necessity to store large volume of data that has led to the development of optical disk storage medium. Optical disks can be divided into the following categories: 1. Compact Disk/ Read Only Memory (CDROM): CDROM disks are made of reflective metals. CDROM is written during the process of manufacturing by high power laser beam. Here the storage density is very high, storage cost is very low and access time is relatively fast. Each disk is approximately 4 1/2 inches in diameter and can hold over 600 MB of data. As the CDROM can be read only we cannot write or make changes into the data contained in it. 2. Write Once, Read Many (WORM): The inconvenience that we can not write any thing in to a CDROM is avoided in WORM. A WORM allows the user to write data permanently on to the disk. Once the data is written it can never be erased without physically damaging the disk. Here data can be recorded from keyboard, video scanner, OCR equipment and other devices. The advantage of WORM is that it can store vast amount of data amounting to gigabytes (109 bytes). Any document in a WORM can be accessed very fast, say less than 30 seconds. 3. Erasable Optical Disk: These are optical disks where data can be written, erased and rewritten. This also applies a laser beam to write and rewrite the data. These disks may be used as alternatives to traditional disks. Erasable optical disks are based on a technology known as magnetic optical (MO). To write a data bit on to the erasable optical disk the MO drive's laser beam heats a tiny, precisely defined point on the disk's surface and CD Disks 1. Speed: Much slower than hard disks. The original CDROM
specification is now given a value of 1x speed, and later, faster CDROMs are quoted as a multiple of this value. Thus, a 50x CDROM is 50 times as fast as the original 1x speed CDROM specification. 3. Capacity: Around 650 Mbytes. 4. Cost: CD drives are becoming very inexpensive. The disks themselves are so cheap that they are often given away when they contain samples or demo software (i.e. Free versions).
DVD Dr ives
1. Speed: Much faster than CD drives but not as fast as hard disks. 2. Capacity: Up to 17 Gbytes. 3. Cost: Slightly higher than CD drives.
6. PEN DRIVES : The Pen Drive has the flash memory that is used in it. The Pen Drive is usually connected to the USB port that is available in the computer motherboards. The USB port or as the abbreviation stands for the Universal Data Bus is the most popular type of connector these days to provide the connection to the many different devices. There is also available these days the mouse that has the USB connectivity. Mostly the USB connector is used for the connection of the printers. The USB as a matter of fact has become so popular these days that its place is brought to the front of the computer from the previously rear end of the computer case. This shows a sort of promotion. Hence it means that there are many devices that are available now that utilize the services of the USB port. The pen drive is also one among them. The kind of memory used in the Pen Drive is the flash memory. This Flash memory is gaining momentum in almost all type of devices that utilize the services of the digital memory. The flash memory chips are available in the market for even enhancing the
existing memory capacity. The pen drive is actually the USB flash memory. The conventional name may be same as that of the USB flash memory. But the name given here is to catch the attention of the customer. The pen drive is so called because it has the memory that is built in the drive and is similar to the shape of the pen. The features like the compactness and sleek look make it very popular. The pen drive is usually so designed for the purpose of the data transfer. The other features like the mp3 players and the radio or the key chain etc may be available with it but in normal conditions are optional. These are available in the memory capacity that may start the range from 32 MB to as much as 2 GB presently. In the near future it is expected that the storage capacity will still be upgraded. The concept involved in the pen drive is that the memory is stored in the form of the array where in the information or the data is stored. The information or the data is stored in the form of the array of transistors. This array of transistors is called as the cells. Each of these cells stores at least one bit of information traditionally. But due to the advancements in the technology the newer versions may even have multi level cells. The data can be stored in more than a bit or specifically only one bit per cell. This is done by the technique of varying the number of electrons that are placed over the floating gate of the cell. The concept of the flash memory is based on the principle of the Floating Gate Avalanche Injection Metal Oxide Semiconductor or in short referred to as the FAMOS transistor. This is the NMOS transistor. This transistor has an additional conductor that is suspended in between the source/drain terminals and gate. The flash memory comes usually in two types. These is two types are mentioned below: the first one is the NOR flash and the second one being the NAND flash. The names given to the types of the flash memory actually refer to the type of the logic gate that is used in each storage cell.
The flash memory that is used in the pen drive is actually a non volatile memory that is the contents remain intact even if there is a power failure.
7. FLASH DRIVES: The type of the memory that is used in the flash drives is the flash memory. The flash memory is a type of chip that is called as the EEPROM. It has the grid that consists of the columns and the rows. It also has a cell. There are two transistors in the cell at each intersection point. The thin oxide layer is responsible for the separation of the two transistors. The first of the transistors is called as the floating gate. The next or the second transistor is called as the control gate. The only link from the floating gate to the row or the word line is through the other gate that is the control gate. If this is working properly then the cell the value of 1 is there. If the value is to be changed to the 0 then the process known as the tunneling or appropriately known as the Fowler Nordheim tunneling is used. The most useful examples include the following that are listed below: That is these are the things where in you can find the flash memory. The first one is the BIOS of any computer. The other examples include the compact flash, smartmedia, PCMCIA – used in the solid state disks mostly in the laptops (this is of the type I and also of the type II), the memory stick that is found in the digital cameras etc, USB pen drives and so on. The flash drive is also used in the memory cards of the mobiles etc. The electronic memory is currently available in many forms and many different prices. The important properties of the flash memory are that it is much fast and
very much easier in use. The different types of devices where the services of the flash drive can be utilized also include the computer system. Here the flash drive can be efficiently used for the purpose of data transfer and also for can be used for as if the hard disk drive of any computer is used. The flash memory is quite expensive as compared to the hard disk drive. But the major advantage of the flash memory over the hard disk is that it is compact and much efficient for the data transfer. The flash memory is also a type of the solid state storage device. That is it means that there are no mobile parts in it. As in the hard disk there are the platters and the read write head moves over it. This is type of mechanism in the hard disk drive is somewhat mechanical in nature but in the consideration with the flash memory this is not the case. There is no such mechanical component in the flash memory drive. Hence it is a purely electronic device. The other flash types also include the one that is known as the Compact flash card. These compact flash cards were introduced by the Sandisk. This was the case as in the year of 1994. The two things differentiate the compact flash drives from the Smart Media cards: The first one is that they utilize the controller chip in them and the second one is that they are thicker. The Compact flash has small circuit board. This circuit board contains the flash memory chips along with a controller chip. This all is covered in a casing that is much thicker in size than a Smart media card. The concept of the dual voltage is supported by the compact flash. That is they can even operate on a voltage of 3.5 as well as on a voltage of 5 volts. In comparison to the smart media card the hard casing and the controller chip, its weight and size, all add to the complexity of the compact flash drive. But the storage capacity of the compact flash drive is more then the smart media.