Chapter 7 Secondary Storage

Chapter 7 – Secondary storage Storage RAM Pri ar Storage 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. We also need external storage because users need much more storage capacity than is typically a aila le i a o pute ’s p i a o RAM e o .  Secondary storage provides permanent or nonvolatile storage.  Writing is the process of saving information to the secondary storage device.  Reading is the process of accessing information from secondary storage. 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. • A ess speed the amount of time required by the storage device to retrieve data and programs. Hard disks  Sa e files alte i g the ag eti ha ges of the disk’s su fa e to epresent 1s and 0s, Then 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.  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 and provide a large amount of capacity. Store and organize files using : • T a ks—concentric rings on the platter. (Each track is divided into sections called sectors) • Se to s—wedge-shaped sections. • C li de s—run through each track of a stack of platters. Hard disks are sensitive instruments. It is so thin that a smoke particle, fingerprint, dust, or human hair could cause what is known as a head crash.  A head crash o u s he the ha d disk akes o ta t ith the d i e’s ead-write heads. 41 Two types of disks are: 1. 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. 2. External Hard Drives provide slower access and are typically connected to a USB or Thunderbolt port on the system unit and are easily removed.  Because they are easily removed, they are particularly useful to protect or secure sensitive information. And backing up the contents of the internal hard disk and providing additional hard-disk capacity. Performance Enhancements Three ways to improve the performance of hard disks are disk caching, redundant arrays of inexpensive disks, and file compression/ decompression. 1) Disk caching improves hard-disk performance by anticipating data needs. It performs a function similar to cache memory.  improves processing by acting as a temporary high-speed holding area between a secondary storage device and the CPU. As a result, overall system performance is often increased by as much as 30 percent. 2) 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 result is expanded storage capability, fast access speed, and high reliability.  RAID is often used by Internet servers and large organizations. 3) File compression and file decompression increase storage capacity by reducing the amount of space required to store data and programs.  It is frequently used to compress files on DVDs, CDs, and flash drives as well.  File compression also helps to speed up transmission of files from one computer system to another.  File compression programs scan files for ways to reduce the amount of required storage.  A way to reduce required storage : is to search for repeating patterns. 42 Solid-State Storage    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 solidstate storage. 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.  SSDs are faster and more durable than hard disks, and require less power.  SSDs are more expensive and generally have a lower capacity than hard disks.  SSDs are widely used in tablets, smartphones, and other mobile devices. 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. USB Drives or flash drives . These d i es o e ie tl o e t di e tl to a o pute ’s USB po t to t a sfe files . can have capacities ranging from 1 GB to 256 GB. a broad price range to match,( Due to their convenient size and large capacities). Optical Discs   can hold over 128 gigabytes of data. In optical disc technology, : a laser beam alters the surface of a plastic or metallic disc to represent data.  Unlike hard disks: which use magnetic charges to represent 1s and 0s, optical discs use reflected light. The 1s and 0s are represented by flat areas called lands and bumpy areas called pits on the disc surface.  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) store 700 MB .( often store music )  Digital versatile discs (DVDs) can store 4.7 GB-- seven times the capacity of CDs. (Often store movies or software ).  Blu-ray discs (BDs) designed to store hi def (high definition) video, which uses the HD 720 and HD 1080 resolutions.  The name Blu-ray comes from a special blue-colored laser used to read the discs . Each of these optical discs has three basic formats: read only, write once, and rewritable. 43 • Read-only (ROM for read-only memory) discs : cannot be written on or erased by the user.  such as music CDs, DVD movies, and Blu-ray video games .(they 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.  such as CD-R, often used for storing family photos, and DVD-R, often used to store home movies. • Re rita le RW for re rita le or RAM for ra do -access memory) discs are similar to write-once discs except that the disc surface is not permanently altered when data is recorded.  popular for storing and sharing audio, video, and large multimedia presentations. How to add capacity to an optical disc : 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. Adding multiple recording layers: These discs store information on several layers sandwiched together on one side of the disc. Cloud Storage The I te et a ts as a loud of servers that supply applications to clients as a service rather than a p odu t. A d p o ides loud s o age o li e sto age . The benefits / advantages of loud sto age : • Less Mai te a e. • Ha d a e upg ades. • File sharing and collaboration disadvantages of loud sto age: • A ess speed—dependent upon the speed of your Internet o e tio . • File se u it —depe de t upo the loud se i e’s se u it p o edu es. Mass Storage Devices 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 A stategy established by large organaziation to promote efficient and safe use of data across the networks. Some of the mass storage devices that support this strategy are: 44 • File ser ers—dedicated computers with very large storage capacities that provide users access to fast storage and retrieval of data. • Net ork atta hed 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. • RAID s ste s—enhance organizational security by constantly making backup copies of files o i g a oss the o ga izatio ’s et o ks. • Orga izatio al loud storage—high-speed Internet connection to a dedicated remote storage facility. These facilities contain banks of file servers to offer enormous amounts of storage. Storage Area Network) is a method of using enterprise-level remote storage systems as if they were local to your computer. SANs provide the ability to house data in remote locations and still allow efficient and secure access 45