Chapter 7 Storage

Arithmetic Logic Unit (ALU) Ch 1 – Introduction Ch 2 – Internet & WWW Ch 3 – Application Software Ch 8 – System Software Ch 4 Processor Control Unit Arithmetic Logic Unit (ALU) Control Unit Arithmetic Logic Unit (ALU) Instructions Data Information Memory Input Devices Ch 5 Information Output Devices Ch 6 Data Instructions Instructions Data Information Storage Devices Ch 7

What a storage device does? Hardware that writes records to the medium holds them and reads from Reading Transfers items from storage media to memory Writing Transfers items from memory to 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

Physical material on which a computer keeps info Storage device and a storage medium storage device Hardware that records, holds and retrieves items to and from a storage medium storage medium Physical material on which a computer keeps info

How does storage differ from memory? Stores items for future use, rather than current use Stores for a long time, rather than temporarily Storage is nonvolatile, rather than volatile To work with a file, you read a part (a block of records) from storage (block by block) and place it in memory When you are finished with the block of a file, you write it from memory to the storage

How does volatility compare? Contents of storage retained when power is off - nonvolatile Screen display and contents of RAM are volatile – erased when power is off

What is capacity? Number of bytes storage medium can hold Storage Term Number of bytes Kilobyte Megabyte Gigabyte Terabyte Petabyte KB MB TB GB PB 1 thousand 1 million 1 billion 1 trillion 1 quadrillion Abbreviation

Google believes that the “plummeting price of storage” will allow iPods of the future (2020 A.D. ) to hold “any video ever produced”. Greet class

Access time: The amount of time it takes a storage device to locate an item on a storage medium

What is access time? cost speed Memory (RAM) Flash memory Compact disk Tape Hard Disk cost less expensive more expensive speed faster slower Amount of time it takes device to locate block on disk – measured in millisec / microsec / nanosec / picosec

Flash Memory Cards and USB Flash Drives What is transfer rate? Time required to deliver a block from storage to memory in kilobytes/sec (KB/sec) or megabytes/sec (MB/sec) Floppy Disk Small files to be transported Secondary Storage Primary Storage Hard Disk Flash Memory Cards and USB Flash Drives CDs and DVDs Tape Items waiting to be interpreted and executed by the processor Operating system, application software, user data and information Digital pictures or files to be transported Software, backups, movies, music Backups Memory (most RAM) faster transfer rates slower transfer rates

Hard disk contains one or more inflexible, circular platters that use magnetic particles to store data, instructions, and information

Revolutions per Minute Characteristics of a hard disk: Capacity Platters Read/Write Heads Cylinders Sectors and Tracks Revolutions per Minute Transfer Rate Access Time

Sample: Hard Disk Characteristics Advertised capacity 500 GB Platters 4 Read/write heads 8 Cylinders 16,383 Bytes per sector 512 Sectors per track 63 Sectors per drive 973,773,168 Revolutions per minute 7,200 Transfer rate 300 MB per second Access time 8.5 ms

Calculating capacity of a hard drive Sector stores 512 bytes of data 16383 cylinders times 8 tracks in a cylinder times 63 sectors per track times 512 bytes per sector = 500 GB

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)

Track Track Arm Head Sector Platter Cylinder Hard Disk Terminology

platter track sector read/write head platter sides cylinder

Cylinder is the collection of single tracks through all platters Track is the narrow recording band that forms full circle on disk surface Cylinder is the collection of single tracks through all platters Single movement of read/write head arms can read any track on the cylinder cylinder track

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 A smoke particle, dust particle, or human hair could render drive unusable

How does RAID work? Redundant Array of Independent Disks Disk system that duplicates data, instructions, and information to improve data reliability Mirroring has one backup disk for each primary disk mirroring (RAID Level 1)

External hard disk—freestanding hard disk that connects to system unit Removable hard disk— you insert and remove from hard disk drive

What is a disk cache? Portion of memory that processor uses to store frequently accessed items first request for data goes to disk cache second request for data goes to hard disk

Disk History 1973: 140 MB 1979: 2,300 Mbytes = 2.3 GB

1 inch disk drive! Hitachi 2007 release Development driven by iPods & digital cameras 20GB, 5-10MB/s

Generate less heat and consume less power Flash Memory Storage Flash memory chips contain no moving parts – solid state drives; they have several advantages over magnetic hard disks: Faster access time Faster transfer rates Generate less heat and consume less power Last longer

USB flash drives plug into a USB port on a computer or mobile device

Secure Digital High Capacity (SDHC) A memory card is a removable flash memory that you insert and remove from a slot in a computer CompactFlash (CF) Secure Digital (SD) Secure Digital High Capacity (SDHC) microSD microSDHC xD Picture Card Memory Stick Memory Stick Micro (M2)

What are PC Cards? Add capabilities to computer Credit-card-sized device commonly used in notebook computers

What is a smart card? Stores data on microprocessor embedded in small card Input, process, output, and storage capabilities

Cloud Storage

What are advantages of an Internet storage? Accessibility Files can be accessed from any computer or device with Web access When in need Large audio, video, and graphics files can be downloaded to an Internet hard drive Share Others can be authorized to access data from your Internet hard drive Security Allows offsite backups of data

Reasons to subscribe to cloud storage: Access files from any computer Store large files Allow others to access their files View data and images Store offsite backups Provide data center functions

What are optical discs? Push the button to slide out the tray. Flat, round, portable discs made of metal or plastic Can be read only or read/write Insert the disc, label side up. Most PCs include an optical disc drive Push the same button to close the tray.

How does a laser read data on an optical disc? laser diode prism light- sensing diode 1 lens pit land disc label Step 3. Reflected light sends digital signals of 1 to computer. Absence of reflected light is read as digital signal of 0. Step 2. If light strikes a pit, it scatters. If light strikes a land, it is reflected back toward diode. Step 1. Laser diode shines a light beam toward disc.

How is data stored on an optical disc? Data is stored in single track Track divided into evenly sized sectors that store items single track spirals to edge of disc disc sectors

How should you care for an optical disc?

X is 150 KBps (KB per second) What is the data transfer rate of a CD drive? 75X 75  150 KBps = 11,250 KBps or 12.25 MBps Ranges from 48X to 75X X is 150 KBps (KB per second) 48X: 48  150 KBps = 7,200 KBps or 7.2 MBps

A CD-ROM can be read from but not written to A CD-R is an optical disc on which users can write, but not erase A CD-RW is an erasable disc

What is a CD-ROM? Compact disc read-only memory Cannot erase or modify contents Typically holds 650 MB to 1 GB Commonly used to distribute multimedia and software

What are CD-Rs and CD-RWs? Must have CD recorder or CD-R drive CD-R (compact disc-recordable) you can write on once Cannot erase disc’s contents CD-RW (compact disc-rewritable) disc you can write on multiple times Must have CD-RW software and CD-RW drive

What is a DVD-ROM (digital video disc-ROM)? Must have DVD-ROM drive or DVD player to read DVD-ROM Stores databases, music, complex software, and movies Blu-Ray discs have storage capacity of up to 100 GB HD-DVD discs have storage capacity of up to 60 GB

Other Types of Storage Magnetic stripe cards and smart cards Tape Microfilm and microfiche Enterprise storage

What is a tape? Magnetically coated plastic ribbon capable of storing large amounts of data at low cost Used for backup

What is sequential access versus direct access? Reading and writing data consecutively Method used for tape direct access You can locate a particular data item or file immediately Method used for hard disks, and compact discs Also called random access

How is data stored on a tape? Sequential access Reads and writes data consecutively, like music tape Unlike direct access ( used on hard disks, CDs, and DVDs ) which can locate particular item much faster

A magnetic stripe card A smart card contains a magnetic stripe that stores information A smart card stores data on a microprocessor embedded in the card

Microfilm and Microfiche Store microscopic images of documents on roll or sheet of film Images are recorded using computer output microfilm recorder Microfilm — 100- to 215-foot roll of film Microfiche — small sheet of film, usually 4”  6”

Enterprise storage stores huge volumes of data and information for large businesses Uses special hardware for heavy use, maximum availability, and maximum efficiency

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