CHAPTER 8: TYPES OF STORAGE


Storage

• Storage holds data,instructions,and information for future use.
• A storage medium is the physical material on which a computer keeps data,instruction,and information.
• Capacity is the number of bytes a storage medium can hold.
• A storage device is the computer hardware that records and/or retrieves items to and from storage media.
• Reading is the process of transferring items from a storage medium into memory.
• Writing is the process of transferring items from memory to a storage medium.
• Access time measures:
• The amount of time it takes a storage device to locate an item on a storage medium.
• The time required to deliver an item from memory to the processor.

Hard Disks

• A hard disk contains one or more inflexible,circular platters that use magnetic particles to store data,instructions, and information.
• Hard disks can store data using longitudinal recording or perpendicular recording.
• Characteristics of a hard disk include:
• Capacity
• platters
• Read/Write heads
• cylinders
• sectors and tracks
• revolutions per Minute
• Transfer Rate
• Access Time
• Formatting is the process of diving the disk into tracks and sectors so that the operating system can store and locate data and information on the disk.

How a Hard Disks Works

Step 1: The circuit board controls the movement of the head actuator and a small motor.

Step 2: A small motor spins the platters while the computer is running.

Step 3: When software requests a disk access,the read/write heads determine the current or new location of the data.

Step 4: The head actuator positions the read/write head arms over the crrect location on the platters to read or write data.

• The hard disk arms move the read/write head,which reads items and writes items in the drive.
• Location often is referred to by its cylinder.
• A head crash occurs when a read/write head touches the surface of a platter.
• Always keep a backup of your hard disk.

How Disk Cache Works

Step 1: A special-purpose chip on the hard disk, called a controller,receives a request for data,instructions,or information from the processor.

Step 2: The controller first checks disk cache for the requested item.

Step 3: If the controller does not find the requested item in disk cache,it locates the requested item on the hard disk's platters.

Step 4: The controller transfers the requested item to the processor.

• RAID (REDUNDANT ARRAY OF INDEPENDENT DISKS) is a group of two or more integrated hard disks.
• A network attached storage (NAS) device e is a server connected to a network with the sole purpose of providing storage.
• An external hard disk is a separate free-standing hard disk that connects to your computer with a cable or wirelessly.
• A removable hard disk is a hard disk that you insert and remove from a drive.
• Internal and external hard disks are available in miniature sizes(miniature hard disks).
• A disk controller consists of a special-purpose chip and electronic circuits that control the transfer of data,instructions ,and information from a disk to and from the system bus and other components of the computer.
• SATA
• EIDE
• SCSI
• SAS

Flash Memory Storage

• Flash memory chips are a type of solid state media and contain no moving parts.
• Solid state drives (SSDs) have several advantages over magnetic hard disks:
• Faster access time
• Faster transfer rates
• Generate less heat and consume less power
• Last longer
• A memory card is a removable flash memory device that you insert and remove from a slot in a computer,mobile device,or card reader/writer.
• Compact Flash(CF)
• Secure Digital (SD)
• Secure Digital High Capacity (SDHC)
• microSD
• microSDHC
• xD Picture Card
• Memory Stick
• Memory Stick Micro (M2)
• USB flash drives plug into a USB port on a computer or mobile device.
• An Express Card module is a removable device that fits in an Express Card slot.
• Developed by the PCMCIA.
• Commonly used in notebook computers.

Cloud Storage

• is an Internet service that provides storage to computer users.
• Users subscribe to cloud storage for a variety of reasons:
• Access files from any computer
• Store large files instantaneously
• Allow others to access their files
• View time-critical data and images immediately
• Store offsite backups
• Provide data center functions

Optical Discs

• An optical disc consists of a flat,round,portable disc made of metal,plastic,and lacquer that is written and read by a laser.
• Typically store software,data,digital photos,movies,and music.
• Read only vs. rewritable

How a Laser Reads Data on an Optical Disc

Step 1: A laser diode shines a light beam toward the disc.

Step 2: If light strikes a pit, it scatters.If light strikes a land, it is reflected back toward the laser diode.

Step 3: Reflected light is deflected to a light-sensing diode,which sends a digital signal of 1 to the computer.Absence of reflected light is read as a digital signal of 0.

• Optical discs commonly store items in a single track that spirals from the center of the disc to the edge.
• Track is divided into evenly sized sectors.
• A CD-ROM can be read from but not written to
• Read from a CD-ROM drive or CD-ROM player.
• A CD-R is a multisession optical disc on which users can write,but not erase.
• A CD-RW is an erasable multisession disc
• Must have a CD-RW drive
• A DVD-ROM is a high-capacity optical disc on which users can read but not write or erase
• Requires a DVD-ROM drive
• A Blu-ray Disc-ROM (BD-ROM) has a storage capacity of 100GB.
• DVD-RW,DVD+RW, and DVD+RAM are high-capacity rewritable DVD formats.

Other Types of Storage

• Tape 
• Tape is a magnetically coated ribbon of plastic capable of storing large amounts of data and information.
• A tape drive reads and writes data and information on a tape.
• Magnetic stripe cards and smart cards
• A magnetic stripe card contains a magnetic stripe that stores information.
• A smart card stores data on a thin microprocessor embedded in the card.
• Microfilm and microfiche
• store microscopic images of documents on a roll or sheet film.
• Enterprise storage
• Enterprise storage stores huge volumes of data and information for large businesses
• Uses special hardware for heavy use,maximum availability,and maximum efficiency.

Putting It All Together

• Home user
• 500 GB hard disk
• Cloud storage
• Optical disc driver
• Card reader/writer
• USB flash drive
• Small Office/Home Office user
• 1 TB hard disk
• Cloud storage
• Optical disc drive
• External hard disk for backup
• USB flash drive
• Mobile
• 250 GB hard disk
• Cloud storage
• Optical disc drive
• Card reader/writer
• Portable hard disk for backup
• USB flash drive
• Power User
• 2.5 TB hard disk
• Cloud storage
• Optical disc drive
• Portable hard disk for backup
• USB  flash drive
• Enterprise User (desktop computer)
• 1 TB hard disk
• Optical disc drive
• Smart card reader
• Tape drive
• USB flash drive
• Enterprise User (server or mainframe)
• Network storage server
• 40 TB hard disk system
• Optical disc server
• Microfilm or microfiche