Copyright: Louise Henry at GSU - CS
Chapter 7: Storage
Memory Versus Storage
What is storage?
; Media and devices used to store and retrieve data, instructions, and information How does storage differ from memory?
; (Memory is also called primary storage or RAM)
; Storage (also called secondary storage):
; Stores items for future use, rather than temporarily
; Storage is nonvolatile, rather than volatile
; When you want to work with a file, you read it from storage and place it in memory ; When you are finished with the file, you write it from memory into storage How does volatility compare?
; Screen display and contents of most RAM (memory) erased when power is off ; Contents of storage retained when power is off
What is a storage device and a storage medium?
; Storage device
o Hardware that records and retrieves items to and from a storage medium ; Storage medium
o Physical material on which a computer keeps data, instructions, and information What is reading and writing?
o Process of transferring data, instructions, and information from a storage medium into
o Serves as a source of input
o Process of transferring items from memory to a storage medium
o Serves as a source of output
What is access time?
; Amount of time it takes device to locate item on disk
; Defines speed of disk storage device
o Tape (slowest, least expensive)
o Floppy Disk
o Compact Disc
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o Hard Disk
What is capacity?
; Number of bytes (characters) storage medium can hold
o Kilobyte KB – 1 thousand
o Megabyte MD – 1 million
o Gigabyte GB – 1 billion
o Terabyte TB – 1 trillion
o Petabyte PB – 1 quadrillion
What is a floppy disk?
; Portable, inexpensive storage medium
; Today’s standard disk is 3.5” wide
; HD (High Density disk) Stores 1.44MB
What are the parts of a floppy disk?
; Thin, circular, flexible film enclosed between two liners How are floppy disk drives designated?
; One floppy drive
o drive A
; Two floppy drives
o drive A
o drive B
How does a floppy disk drive work?
; 1: Shutter moves to expose recording surface on disk ; 2: Signal sent to control movement of read/write heads and disk ; 3: If write instruction, circuit board verifies whether disk can be written to
; 4: Motor causes floppy disk to spin
; 5: Motor positions read/write heads over correct location on disk ; 6: Read/write heads read data from or write data on the floppy disk What are tracks and sectors?
; Track is narrow recording band that forms full circle on disk surface ; Sector can store up to 512 bytes of data
o 80 tracks per side X 18 sectors per track X 2 sides per disk X 512 bytes per sector =
1,474,560 bytes = 1.44 MB
What is formatting?
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; Process of preparing disk for reading and writing
; Formatting marks bad sectors as unusable
How do you care for a floppy?
; Proper care helps maximize disk’s life
; Floppy disk can last at least seven years
o Never open the shutter and touch the disk’s recording surface
o Avoid exposure to heat and cold
o Avoid exposure to magnetic fields
o Avoid exposure to contaminants such as dust, smoke, or salt air
o Keep disks in a storage tray when not using them What is a write-protect notch?
; Small opening with a cover that you slide
; Protects floppy disks from being erased accidentally
o notch open means you cannot write on the disk
o notch closed means you can write on the disk
What is a high-capacity disk drive?
; Uses disks with capacities of 100 MB and greater
; Primarily used to backup files and transfer files
o Zip? drive
o Uses a Zip? disk that can store 100 MB or 250 MB of data What is a backup?
; Duplicate of file, program, or disk that you can use if original is lost, damaged, or destroyed
What is a hard disk?
; High-capacity storage (20 – 100 GB)
; Consists of several inflexible, circular platters that store items electronically
; Components enclosed in airtight, sealed case for protection How does a hard disk work?
; 1: Circuit board controls movement of head activator and small motor ; 2: Small motor spins platters
; 3: When software requests disk access, read/write heads determine location of data
; 4: Head actuator positions read/write head arms over correct location on platters to read or write data
What is a cylinder?
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; Location of a single track through all platters
; Single movement of read/write head arms can read same track on all platters What is a head crash?
; Occurs when read/write head touches platter surface
; Spinning creates cushion of air that floats read/write head above platter
o clearance between head and platter is approximately two millionths of an inch
o gap is half the diameter of a dust particle
What is a disk cache?
; Portion of memory processor uses to store frequently accessed items What is a partition?
; Formatted hard disk divided into separate areas called partitions ; Each partition functions as if it were a separate hard disk drive ; Designation for first partition or for a single partition on hard disk
o drive C
; Designation for second partition on hard disk
o drive D
What is a removable hard disk?
; Disk drive in which a plastic or metal case surrounds the hard disk so you can remove it from the
; Used for backup or to transfer files
How does RAID work?
; Disk system that duplicates data, instructions, and information to improve data reliability ensuring
that data is not lost if one drive fails
o Mirroring has one backup disk for each disk
o Striping stores data across multiple disks
What Windows utilities maintain a hard disk drive?
; Disk Cleanup
; Disk Defragmenter
; Scheduled Tasks
What is an Internet hard drive?
; Service on Web that provides storage to computer users
o Most offer free storage
o Revenues come from advertisers
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What are advantages of an Internet hard drive?
; Large audio, video, and graphics files can be downloaded to an Internet hard drive instantaneously
; Files can be accessed from any computer or device with Web access ; Others can be authorized to access data from your Internet hard drive ; Allows offsite backups of data
What is a compact disc (CD)?
; Storage medium
; Most PCs include some type of compact disc drive ; Available in variety of formats
How do you use a compact disc?
; CD drives can read compact discs, including audio discs How does a laser read data on a compact disc?