SECONDARY STORAGE
Introduction :-
Secondary storage devices are used to save create backup, and even transport files consisting of data or programs from one cation or computer to another. At one time, most all files contained only numbers and letter. The demands for saving these files were easily met with low-capacity storage devices Data storage has expanded from text and numeric files to include digital music files photographic files, video files, and much more. These new types of files require secondary storage devices that have much greater capacity.
Secondary storage devices have always been an indispensable element in any computer system. They have similarities to output and input devices. Like output devices, secondary storage devices receive information from the system unit in the form of the machine language of Os and 1s. Rather thant translating the information, secondary storage devices save the information in machine language for later use. Like input devices, secondary storage devices send information to the system unit for processing. However, the information, since it is already in machine form, does not need to be translated. It is sent directly to memory (RAM), where it can be accessed and processed by the CPU.
To efficiently and effectively use computers, you need to be aware of the different types of secondary storage. You need to know the capabilities, limitations, and uses of hard disk, solid-state drives, optical discs, cloud storage, and other types of secondary storage. Additionally, you need to be aware of specialty storage devices for portable computers and to be knowledgeable about how large organizations manage their extensive data resources.
An essential feature of every computer is the ability to save, or store, random-access memory (RAM) holds or stores data and programs that the CPU is presently processing. Before data can be processed or a program can be run, it must be in RAM. For this reason, RAM is sometimes referred to as primary storage.
Secondary storage provides permanent or nonvolatile storage. Using secondary storage devices such as a hard-disk drive data and programs can be retained after the computer has been shut off. This is accomplished by writing files to and reading files from secondary storage devices. Writing is the process of saving information to the secondary storage device. Reading is the process of accessing information from secondary storage. This chapter focuses on secondary storage devices.
These are important characteristics of secondary storage:
● Media are the physical material that holds the data and programs.
● Capacity measures how much a particular storage medium can hold.
● Storage devices are hardware that reads data and programs from storage media. Most also write to storage media.
● Access speed measures the amount of time required by the storage device to retrieve data and programs.
Most desktop personal computer systems have hard-disk and optical disc drives, as well as ports where additional storage devices can be connected.
HARD DISKS
Hard disk save files by altering the magnetic charge of the disk's surface io represent 1s and Os. Hard disk retrieve data and programs by reading these charges from the magnetic disk. Characters are represented by positive (+) and negative (-) charges using the ASCII, EBCDIC, or Unicode binary codes. For example, the letter A would require a series of 8 charges. Density refers to how tightly these charges can be packed next to one another on the disk.
Hard disks use rigid metallic platters that are stacked one on top of another. Hard disks store and organize files using tracks, sectors, and cylinders. Tracks are rings of concentric circles on the platter. Each track is divided into invisible wedge-shaped sections called sectors. A cylinder runs through each track of a stack of platters. Cylinders are necessary to differentiate files stored on the same track and sector of different platters. When a hard disk is formatted, tracks, sectors, and cylinders are assigned.
Hard disks are sensitive instruments. Their read/write heads ride on a cushion of air about 0.000001 inch thick It is so thin that a smoke particle. fingerprint, dust, or human hair could cause what is known as a head crash.
There are two basic types of hard disks: internal and external.
◆ INTERNAL HARD DISK
An internal hard disk is located inside the system unit. These hard disks are able to store and retrieve large quantities of information quickly. They are used to store programs and data files. For example, nearly every personal computer uses its internal hard disk to store its operating system and major applications such as Word and Excel.
To ensure adequate performance of your internal hard disk and the safety of your data, you should perform routine maintenance and periodically make backup copies of all important files.
◆ EXTERNAL HARD DRIVES
While internal hard disk provide fast access, they have a fixed amount of storage and cannot be easily removed from the system unit. External hard disks provide slower access and are typically connected to a USB or Thunderbolt port on the system unit and are easily removed. Like an internal hard disk, external hard disks have a fixed amount of storage. However, since each removable hard disk can be easily replaced by another removable hard disk, a single por on the system unit can provide access to an unlimited amount of storage.
● PERFORMANCE ENHANCEMENTS
Three ways to improve the performance of hard disks are disk caching, redundant arrays of inexpensive disks, and file compression/ decompression.
Disk caching improves hard-disk performance by anticipating data needs. It performs a function similar to cache memory. While cache memory improves processing by acting as a temporary high-speed holding area between memory and the CPU, disk caching improves processing by acting as a temporary high-speed holding area a between secondary storage device and the CPU. Disk caching requires a combination of caching hardware and software.
During idle processing time, frequently used data is automatically identified and read from the hard disk into the disk cache. When needed, the data is then accessed directly from memory. The transfer rate from memory is much faster than from the hard disk. As a result, overall system performance is often increased by as much as 30 percent.
Redundant arrays of inexpensive disks (RAID) improve performance by expanding external storage, improving access speed, and providing reliable storage. Several inexpensive hard disk drives are connected to one another. These connections can be by a network or within specialized RAID devices. The connected hard-disk drives are related or grouped together, and the computer system interacts with the RAID system as though it were a single large-capacity hard-disk drive. The result is expanded storage capability, fast access speed, and high reliability. For these reasons, RAID is often used by Internet servers and large organizations.
File compression programs scan files for ways to reduce the amount of required storage. One way is to search for repeating patterns. The repeating patterns are replaced with a token, leaving enough tokens so that the original can be rebuilt or decompressed These programs often shrink files to a quarter of their original size.
Windows and Mac operating systems provide compression and decompression utilities. For more advanced compression schemes, you can use specialized utilities such as WinZip. For summary of performance enhancement techniques.
SOLID-STATE STORAGE
Unlike hard disks, which rotate and have read/write heads that move in and out, solid-state storage devices have no moving parts. Data and information are stored and retrieved electronically directly from these devices much as they would be from conventional computer memory.
Solid-state storage devices provide access to flash memory, also known as solid-state storage. As we discussed in Chapter 5, flash memory offers a combination of features of RAM and ROM. Like RAM it can be updated and like ROM it does not lose information when a computer is turned off. Flash memory is a little slower than traditional memory but much faster than traditional hard disks.
SOLID-STATE DRIVES
Solid-state drives (SSDs) are designed to be connected inside a personal computer system the same way an internal hard disk would be but contain solid- state memory instead of magnetic disks to store data.
FLASH MEMORY CARDS
Flash memory cards are small solid-state storage devices widely used in portable devices. Some of the cards are used within devices such as laptops, smartphones, and GPS navigation systems. Other cards provide removable storage. For example, flash memory is used to store images captured from digital cameras and then to transfer the images to desktop and other computers. Flash memory is used in digital media players like the iPod to store and play music and video files.
USB DRIVES
USB drives, or flash drives, are so compact that they can be transported on a key ring. These drives conveniently connect directly to a computer's USB port to transfer files and can have capacities ranging from 1 GB to 256 GB, with a broad price range to match. Due to their convenient size and large capacities, USB drives have become a very popular option for transporting data and information between computers, specialty devices, and the Internet.
What is solid-state storage?
How is it different from hard-disk drives?
What are solid-state drives?
What are they used for?
What are flash memory cards?
What are USB drives?
What are they used for?
OPTICAL DISCS
Today's optical discs can hold over 128 gigabytes of data. I That is the equivalent of millions of typewritten pages or a medium-sized library all on a single disc. Optical discs are very common, with most software and many movies available on optical disc.
Like hard disks, optical discs use tracks and sectors to organize and store files. Unlike the concentric tracks and wedge-shaped sectors used for hard disks, however, optical discs typically use a single track that spirals outward from the center of the disc. This single track is divided into equal sized sectors.
The most widely used optical discs are CD, DVD, and Blu-ray discs.
● Compact discs (CDs) were the first widely available optical format for PC users. Typically. CD drives store 700 MB (megabytes) of storage. Optical discs that store music are often CDs.
● Digital versatile discs (DVDs) are the standard optical discs in PCs. DVDs are very similar to CDs except that typical DVD disc can store 4.7 GB (gigabytes) seven times the capacity of CDs. Optical discs that store movies or software are often DVDs, DVD drives and CD drives look very similar.
● Blu-ray disc ( BDS ) are the newest form of optical storage designed to store hi def (high definition) video, which uses the HD 720 and HD 1080 resolutions discussed in Chapter 6. The name Blu-ray comes from a special blue-coloured laser used to read the disc that gives them a typical capacity of 50 GB- ten times the capacity of DVDs Optical disks that store high def video and the newest video games are often Blu-ray discs.
Each of these optic disc has three basic formats: read only, write once, and rewritable,
● Read-only (ROM for read-only memory) discs are diseases that cannot be written on or erased by the user. Optical discs that you buy in a store, such as music CDs DVD movies, and Blu-ray video games, are often read only.
● Write-once (R for recordable) discs can be written on once. After that, the disc can be read many times but cannot be written on or erased. These discs are ideal for creating permanent archives, such as CD-R, often used for storing family photos, and DVD-R, often used to store home movies.
● Rewritable (RW for rewritable or RAM for random-access memory) discs are similar to write-once discs except that the disc surface is not permanently altered when data is recorded. These changeable, portable storage options are popular for storing and sharing audio, video, and large multimedia presentations.
Some optical discs, referred to as double-sided discs, contain information on both sides of the disc and need to be flipped over to read the other side, effectively doubling the storage capacity of the disk. For example, a double-sided DVD can store 9.4 GB, or twice as much as a single-sided DVD. Another way to add capacity to an optical disc is by adding multiple recording layers. These discs store information on several layers sandwiched together on one side of the disc. For example, some Blu-ray discs have multiple layers that increase storage capacity from 50 GB to 128 GB.
CLOUD STORAGE
Recently, many applications that would have required installation on your Computer to run have moved to the web. This is known as cloud computing, where the Internet acts as a "cloud" of servers that supply applications to clients as a service rather than a product. Additionally, these servers provide cloud storage, also known as online storage.
If you have used Google Drive Docs to create a word processing document or a spreadsheet, you have already used cloud computing. The service provider's server runs the applications and your computer displays results, The applications and data can be accessed from any Internet-ready device. This means that even devices with little storage, memory, or processing power, such as a smartphone, can run the same powerful applications as a desktop computer.
The benefits to this arrangement are numerous:
● Maintenance -The cloud service will take care of disk defragmentation, backups, encryption, and security.
● Hardware upgrades -The cloud service will never run out of disk space and can replace failed hard disk without interruption to the User.
● File sharing and collaboration- Users can share documents, spreadsheets, and files with others from anywhere with an Internet connection.
Of course, there are some disadvantages of cloud storage:
● Access speed-The data transfer rate is dependent upon the speed of your Internet connection, which most likely is not as fast as a user's internal network.
● File security- Users are dependent upon the cloud service's security procedures, which may not be as There are numerous websites that provide cloud storage services.
Questions :-
What is cloud computing?
What is cloud storage?
What are some of the advantages and disadvantages of cloud storage?
MASS STORAGE DEVICES
It is natural to think of secondary storage media and devices as they relate to us as individuals. It may not be as obvious how important these matters are to organizations. Mass storage refers to the tremendous amount of secondary storage required by large organizations: Mass storage devices are specialized high-capacity secondary storage devices designed to meet organizational demands for data storage. These mass storage solutions allow large corporations and institutions to centralize their maintenance and security of data, thereby reducing costs and personnel.
ENTERPRISE STORAGE SYSTEM
Most large organizations have established a strategy called an enterprise storage system to promote efficient and safe use of data across the networks within their organizations. Some of the mass storage devices that support this strategy are:
● Network attached storage (NAS)-a type of file server designed for homes and small businesses. NAS is less expensive, easier to set up, and easier to manage than most file servers. However, it does not include powerful management tools and features found in many large-scale file servers.
● RAID systems-larger versions of the specialized devices discussed earlier in this chapter that enhance organizational security by constantly making backup copies of files moving across the organization's networks.
● Organizational cloud storage-high-speed Ite connection to a dedicated remote storage facility. These facilities contain banks of file servers to offer enormous amounts of storage.
STORAGE AREA NETWORK
A recent mass storage development is storage area network (SAN) systems. SAN is an architecture to link remote computer storage devices, such as enterprise storage systems, to computers such that the devices are as available as locally attached drives. In a SAN system, the user's computer provides the file system for storing data, but the SAN provides the disk space for data.
The key to a SAN is a high-speed network connecting individual computers to mass storage devices. Special file systems prevent simultaneous users from interfering with each other SANS provide the ability to house data in remote locations and still allow efficient and secure access.
Questions :-Define mass storage and mass storage devices.
What is an enterprise storage system?
What is a storage area network system?
