Unit 3 Storage Devices Section C

Chapter 1, Slide 2Starting Out with Visual Basic 3 rd EditionIntroduction to ComputersUnit 3C – Storage DevicesSlide 2 Storage devices are designed for long-term, non-volatile retention of electronic data A storage medium is a disk, tape, CD, DVD or other recording surface that retains data A storage device records and reads the data on the storage medium Hard disk and flash memory combine the medium and device into one unit Floppy disk, CD, DVD, and tape allow the media to be removed from the device

Chapter 1, Slide 3Starting Out with Visual Basic 3 rd EditionIntroduction to ComputersUnit 3C – Storage DevicesSlide 3 Magnetic storage Includes hard disk, floppy disk, tape Magnetizes tiny particles on disk surface Optical storage Includes CDs and DVDs Stores data as tiny light spots (lands) or dark spots (pits) on the disk surface Flash memory A non-volatile form of solid state memory circuitry

Chapter 1, Slide 4Starting Out with Visual Basic 3 rd EditionIntroduction to ComputersUnit 3C – Storage DevicesSlide 4 Magnetic storage device has a read/write head Data written by magnetizing particles on a surface Magnetization can later be read and deciphered Susceptible to dust, smoke, heat, but especially magnetic or strong electrical fields Don’t put a floppy disk close to a powerful speaker Speakers contain magnets and can erase a floppy Magnetic media tends to degrade over time But this process takes years

Chapter 1, Slide 5Starting Out with Visual Basic 3 rd EditionIntroduction to ComputersUnit 3C – Storage DevicesSlide 5 A laser is directed at the surface of the disk The pattern of dark and light spots is reflected back The pattern of reflected light is read as data CDs and DVDs much less sensitive to damage Fairly insensitive to dust, smoke, heat Not magnetic so not harmed by electrical fields Does not degrade over time Generally more reliable than magnetic media But slower access time and more difficult to write to

Chapter 1, Slide 6Starting Out with Visual Basic 3 rd EditionIntroduction to ComputersUnit 3C – Storage DevicesSlide 6 Functions similar to random access memory But uses a different type of technology Non-volatile, power not needed to maintain data Fast read times but not as fast as RAM Completely electronic, no moving parts Thus highly reliable and very durable Not sensitive to dust, smoke, magnetic fields USB flash memory has replaced floppy disks May replace hard disks at some point

Chapter 1, Slide 7Starting Out with Visual Basic 3 rd EditionIntroduction to ComputersUnit 3C – Storage DevicesSlide 7 PCs have drive bays to hold storage devices Two sizes of drive bays 5 ¼ inch drive bay 3 ½ inch drive bay Laptops also have drive bays

Chapter 1, Slide 8Starting Out with Visual Basic 3 rd EditionIntroduction to ComputersUnit 3C – Storage DevicesSlide 8 Use the following factors when evaluating the relative merits of different types of storage Storage capacity - hard disk and tape largest by far Access speed – hard disk is fastest by far Durability – hard disk, CD, DVD are all very good Portability – CD, DVD, flash memory most portable

Chapter 1, Slide 9Starting Out with Visual Basic 3 rd EditionIntroduction to ComputersUnit 3C – Storage DevicesSlide 9 Principle storage device for most computers Huge storage capacity, 250 to 1000 GB & more Fast access to data Extremely low cost per megabyte Avoids magnetic storage durability issues by operating in a closed environment Manufactured in clean rooms Disk surface permanently enclosed If you remove the cover, you’ll never use it again

Chapter 1, Slide 10Starting Out with Visual Basic 3 rd EditionIntroduction to ComputersUnit 3C – Storage DevicesSlide 10 Often has multiple platters 2 read/write heads for each platter, one for the top and one for the bottom Platters spin at a high rate of speed, 7200 rpm Read/write head moves across the surface to read data anywhere on surface

Chapter 1, Slide 11Starting Out with Visual Basic 3 rd EditionIntroduction to ComputersUnit 3C – Storage DevicesSlide 11 Hard disks are highly reliable but susceptible to: A head crash can damage data on the disk Can occur when dust or other contaminant gets between the read/write head and disk surface Can also occur from jarring hard disk while in use Never move a desktop computer while in use Read/write head retracts from disk when turned off Laptops have shock-mounted hard drives Mechanical failure – any machine can break

Chapter 1, Slide 12Starting Out with Visual Basic 3 rd EditionIntroduction to ComputersUnit 3C – Storage DevicesSlide 12 Removable hard drives Transforms a drive bay into a “drawer” Can slide a removable hard drive into the “drawer” Can easily remove and replace it with another drive External hard drives are designed to be used outside the system unit Connect to the computer through the USB port USB port limitations cause access time to be slower External and removable drives can be terrific as backup devices to save a copy of your hard disk

Chapter 1, Slide 13Starting Out with Visual Basic 3 rd EditionIntroduction to ComputersUnit 3C – Storage DevicesSlide 13 CDs are extremely durable Very inexpensive to manufacture and purchase Ideal for distributing software or other large files Access speed much faster than floppy disk Can create your own CDs with CD-R or CD-RW Great for archiving large files such as photos Good storage capacity, up to 700 MB A CD drive is a necessity for any computer

Chapter 1, Slide 14Starting Out with Visual Basic 3 rd EditionIntroduction to ComputersUnit 3C – Storage DevicesSlide 14 Access speed much slower than a hard disk Storage capacity less than flash memory and far less than hard disk

Chapter 1, Slide 15Starting Out with Visual Basic 3 rd EditionIntroduction to ComputersUnit 3C – Storage DevicesSlide 15 CD-ROM stands for Compact Disk - Read Only Can’t write data to a CD-ROM Can buy CD-R disks, Compact Disk-Recordable Allows you to create your own CDs Can write only once but read as much as you like CD-RW stands for Compact Disk Rewritable Also allows you to create your own CDs Can write and read as often as you like Must have a CD-R or CD-RW drive to do this Most CD drives work with both CD-R and CD-RW

Chapter 1, Slide 16Starting Out with Visual Basic 3 rd EditionIntroduction to ComputersUnit 3C – Storage DevicesSlide 16 CD-R disks are much cheaper than CD-RW So think carefully when buying Do you really need the “rewritable” capability? For example, if archiving photos it’s usually more cost effective to use CD-R It’s unlikely you’ll make further changes to that disk If the data on a CD-R becomes out of date…. Can still use it as a coaster… or a frisbee CD-RWs don’t get out of date, just rewrite them

Chapter 1, Slide 17Starting Out with Visual Basic 3 rd EditionIntroduction to ComputersUnit 3C – Storage DevicesSlide 17 Similar positives to CDs Durable and very inexpensive to manufacture Far better storage capacity, 4.7 GB versus 700 MB Only negative is a slower access speed similar to CD access speeds Must have a DVD drive to read a DVD Most optical drives (but not all) sold today are combo drives that read both CDs and DVDs

Chapter 1, Slide 18Starting Out with Visual Basic 3 rd EditionIntroduction to ComputersUnit 3C – Storage DevicesSlide 18 CD and DVD speed is expressed in an odd way Both are expressed in terms of how many times faster than the 1st model of CD or DVD drive DVD Drive SpeedData Transfer RateCD Drive Speed 1X11.08 Mbps9X 2X22.16 Mbps18X 3X44.32 Mbps36X 4X55.40 Mbps46X

Chapter 1, Slide 19Starting Out with Visual Basic 3 rd EditionIntroduction to ComputersUnit 3C – Storage DevicesSlide 19 Magnetic tape was a popular form of general use storage in the 1960s Tape is no longer a primary storage device Inconvenient and slow, can only read sequentially Tape now used primarily as a backup device High storage capacity, comparable to hard disks Heavily used by businesses for data backup Tape drives are available in both internal and external models

Chapter 1, Slide 20Starting Out with Visual Basic 3 rd EditionIntroduction to ComputersUnit 3C – Storage DevicesSlide 20 Floppy disks have mostly disappeared into the ash heap of history Storage capacity of floppy disks is far too small for today’s needs. They’ve been replaced by USB flash memory devices You still see floppy disks occasionally but soon they’ll only be museum pieces