Presentation on theme: "Storage refers to the media and methods used to keep information available for later use. Main Memory = Primary Storage Computers use RAM, or Random Access."— Presentation transcript:
Storage refers to the media and methods used to keep information available for later use. Main Memory = Primary Storage Computers use RAM, or Random Access Memory. Main memory keeps track of what is currently being processed. It's volatile, meaning that turning the power off erases all of the data.
Auxiliary Storage = Secondary Storage Auxiliary storage holds what is not currently being processed. This is the stuff that is "filed away", but is ready to be pulled out when needed. It is nonvolatile, meaning that turning the power off does not erase it. Used for: Input - data and programs Output - saving the results of processing
Advantages: high storage capacity reliable gives direct access to data Types Hard Disk Floppy Disk Zip Disk
All magnetic disks are similarly formatted, or divided into areas, called tracks, sectors and cylinders. A track is a circular ring on one side of the disk. Each track has a number. The diagram shows 3 tracks.
A disk sector is a wedge-shape piece of the disk, shown in yellow. A track sector is the area of intersection of a track and a sector, shown in yellow.
A cluster is a set of track sectors, ranging from 2 to 32 or more, depending on the formatting scheme in use. A cylinder is a set of matched tracks. What happens when a disk is formatted? 1. All data is erased. 2. Surfaces are checked for physical and magnetic defects. 3. A root directory is created to list where things are on the disk.
Capacity of a Disk depends on: 1. # of sides used: single-sided or double-sided 2. Recording density - how close together the bits can be on a track sector of the innermost track 3. # of tracks on the disk
5¼" floppy - 360 KB or 1.2 MB 3½" floppy - 720 KB or 1.44 MB Hard disk early ones = 20 MB Currently (July 2010) up to 3 TB Internal hard drive where 1 TB = 1 terabyte = 1000 GB
The process of accessing data has 4 steps. 1. Seek - move the head to proper track 2. Rotate - rotate disk under the head to the correct sector 3. Settle - head lowers to disk; wait for vibrations from moving to stop (actually touches only on floppies) 4. Data transfer - copy data to main memory
ms stands for millisecond =.001 second kbs is kilobytes per second Total time to transfer a kilobyte: for floppies, 175 - 300 ms for hard drive, 15 - 80 ms new hard drives (Jun. 2009).0032 ms (300 MB per sec).
Most problems occur when the read/write head (looks like a pointer in the photo) damages the metal disk by hitting or even just touching it. This is called a head crash. Dont ever: Jar the computer while the disk is spinning. Turn the computer off and quickly back on before spinning has stopped. Drop it - ever.
How to safeguard your data: Write protect - This keeps your files from being overwritten with new ones. Backup - Make multiple copies of important data often. Anti-malware - Use a set of programs that continuously look for an attack by a virus, trojan, or worm.
Magnetic tape uses a method similar to that of VCR tape for storing data. Types of Tape: Tape Reel Tape Cassette
Density - Higher density means more data on shorter tape. Measured as bpi = bits per inch Blocks - The tape is divided into logical blocks, as a floppy is divided into tracks and sectors. Gap - Two kinds of blank spots, called gaps, are set on the tape. Interblock gap which separates logical blocks. Interrecord gap which is wider and separates records.
An entirely different method of recording data is used for optical disks. These include the various kinds of CD and DVD discs. How optical disks are similar Formed of layers Data in a spiral groove on starting from the center of the disk Digital data (1's and 0's) 1's and 0's are formed by how the disk absorbs or reflects light from a tiny laser.
The materials used for the data (recording) and metal (reflecting) layers are different for different kinds of optical disks. The most common type of optical disk is the CD- ROM, which stands for Compact Disc - Read Only Memory. DVD used to stand for Digital Video Device or Digital Versatile Device, but now it doesn't really stand for anything at all! DVDs are used for recording movies and large amounts of data.
The optical disks that you can record on your own computer are CD-R, DVD-R, and DVD+R discs, called writable or recordable disks. The data layer is an organic dye that the writing laser changes. Once the laser modifies the dye, it cannot be changed again. Manufacturers say that these disks have a shelf-life of 5 - 10 years before they are used for recording.
An option for backup storage of changing data is rewritable disks, CD-RW, DVD-RW, DVD+RW, DVD+RAM. The data layer for these disks uses a phase- changing metal alloy film. This film can be melted by the laser's heat to level out the marks made by the laser and then lasered again to record new data. In theory you can erase and write on these disks as many as 1000 times, for CD-RW, and even 100,000 times for the DVD-RW types.
Advantages of Optical Disks 1. Physical: An optical disk is much sturdier than tape or a floppy disk. It is physically harder to break or melt or warp. It's somewhat harder to lose than a USB flash drive. 2. Delicacy: It is not sensitive to being touched, though it can get too dirty or scratched to be read. It can be cleaned! 3. Magnetic: It is entirely unaffected by magnetic fields. 4. Capacity: Optical disks hold a lot of data, especial the double-sided DVDs.
Disadvantages of Optical Disks 1. Cost: The main disadvantage has been cost – both for the drive and the disks. 2. Duplication: It is not quite as easy or as fast to copy an optical disk as it is to copy files to a USB flash drive. You need the software and hardware for writing disks!
Data loss comes from: Physical damage - breaking, melting, scratching... Blocking of laser light by dirt, paint, ink, glue... Corrosion of the reflecting layer
Cleaning: Keep it clean! Handle by the edges or center hole. Put it back in its case as soon as you are finished with it. No laying around on the desktop!! Remove dirt and smudges with a clean cotton cloth by wiping from the center to the outer edge, NOT by wiping around the disk. Wiping in a circle can create a curved scratch, which can confuse the laser. For stubborn dirt, use isopropyl alcohol or methanol or CD/DVD cleaning detergent.
Labeling: Don't use an adhesive label. The adhesive can corrupt your data in just a few months! Don't write on or scratch the data side of the disk - ever! Don't scratch the label side. Don't write on the label side with a pencil or pen (scratches!) Don't write on the label side with a fine-point marker or with any solvent-based marker. Use markers for CDs. (Solvent may dissolve the protective layer.)
Storage: Store optical disks upright on edge, like a book, in a plastic case designed specifically for them. Not flat for long periods! Store in a cool, dark environment where the air is clean and dry. NO SMOKE! Low humidity.
How you treat it: Keep away from high heat and high humidity which accelerate corrosion. Keep out of sunlight or other sources of ultraviolet light. Keep away from smoke or other air pollution. Don't bend it! Don't use a disk as a coaster or a frisbee or a bookmarker!
Recording Check disk for flaws and dirt BEFORE recording on it. Only open a recordable disk just before you plan to record on it. After recording, make sure the disk works as you expect: Read data; run programs.